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Tuesday, May 31, 2011

Monitoring Antimicrobial Therapy

Two general types of in vitro tests are used to monitor antimicrobial therapy: measure¬ment of blood or body fluid antibiotic activity against the responsible organism, and assay of actual antibiotic concentrations in blood or other bodily fluids.


I. The serum bactericidal test determines the killing power” of patient serum against the infecting organism. The result is expressed as the highest dilution of serum that will produce the desired effect.

A. Method. The serum bactericidal test involves a modification of the broth dilution technique. Serum usually is obtained from the patient at times believed to correlate with the maximum or minimum antibacterial activity. Serial, twofold dilutions of the patient’s serum are inoculated with a standard quantity of the infecting organism. After overnight incubation of the mixtures, the inhibitory and lethal end points are determined as in broth dilution susceptibility testing, shown sche¬matically in Fig. 25-3. The serum inhibitory or bacteriostatic activity is defined as the highest dilution of serum that demonstrates a visible inhibitory effect. The serum lethal or bactericidal activity is similarly expressed as the highest dilution that produces a lethal effect, usually defined as a 99.9% or greater reduction of viable organisms in the initial inoculum. Bactericidal activity of other bodily fluids such as CSF, urine, and synovial fluid also can he measured by a modification of this method.

1. Variables. The measurement of serum bactericidal activity is influenced by numerous technical variables. These include the type of serum or broth diluents used, whether serum complement is or is not inactivated, the concentration of magnesium and calcium ions in the media, and the definition of the bacteri¬cidal end point. For example, a patient’s serum containing highly protein-bound antibiotics may show greater bactericidal activity if diluted in nutrient broth (which has a low protcin concentration) rather than in pooled human serum (which has a high protein concentration). The lack of interlaboratory standardization in the performance of these tests makes it difficult to com¬pare results between studies (43, 43a].

2. Timing of sample. Several authors favor collection of the serum sample at peak, whereas others prefer trough levels. The utility of peak versus trough serum bactericidal activity remains controversial [431.

B. Clinical application. Many authorities advocate using serum inhibitory or bacteri¬cidal activity as the best indicator of potential therapeutic efficacy. The test is the most reliable in vitro correlate of actual in vivo conditions because it accounts for other components of the antibacterial activity of serum in addition to the antibiotic (i.e., serum complement, opsonins, lysozymes). However, clinical appli¬cability of the serum bactericidal titer remains to be proven rigorously [431, and its use remains somewhat controversial [18, 44]. infectious disease consultation is advised to assist in the appropriate utilization and interpretation of serum bactericidal tests.

A determination of serum bactericidal activity may prove useful in guiding therapy, particularly in the following situations:

1. Endocarditis may be more effectively treated when higher serum bactericidal activity can be achieved. However, the results of serum bactericidal tests are not necessarily predictive of survival or clinical cure, and the peak and trough bactericidal titers that best correlate with outcome are not yet clear [43, 43a, 451. Although a peak bactericidal titer of at least 1:8 is most frequently recommended, one study concluded that a peak titer of 1:64 or more and a trough titer of 1:32 or more were most predictive of bacteriologic cure of endocarditis; the test was a poor predictor of bacteriologic failure [46].

The bactericidal titer may be particularly helpful in the following circum¬stances:

a. When endocarditis is caused by organisms that are not highly sensitive to the antibiotics being used, and a synergistic combination of antibiotics might be more effective

b. When less well established treatment regimens are employed

c. When the patient fails to improve on standard therapy

d. When the serum bactericidal titer is very high and drug toxicity is a significant risk, in which case the drug dose might be reduced without compromis¬ing antibacterial effect

2. In acute and chronic osteomyelitis, serum bactericidal titers that exceed cer¬tain levels have been correlated with cure [47]. When changing from parenteral to oral therapy of acute hematogenous osteomyelitis in children, bactericidal titers often are monitored to adjust antibiotic dosage to achieve a bactericidal level of 1:8 or more [43a]. The usefulness of serum bactericidal tests in the management of osteomyelitis, particularly in adults, remains uncertain.

3. In the immunocompromised host, a serum bactericidal titer of 1:8 or greater has been correlated with successful treatment of bacteremia and soft-tissue infections [48]. Higher bactericidal titers may be desirable in the granulocyto¬penic patient with gram-negative rod bacteremia [49].

4. In patients with acute pulmonary exacerbations of cystic fibrosis, peak serum bactericidal titers of 1:128 or greater against the patients’ pulmonary patho¬gens have been correlated with favorable bacteriologic responses to therapy [50].

II. Antimicrobial levels may be obtained to assess the adequacy of the chosen dose and route of administration and to avoid toxicity [19].

A. Methods

1. Correct timing of samples is necessary for accurate interpretation of the significance of antibiotic levels. The two measurements usually performed are the anticipated peak and trough blood levels of the antimicrobial after a dose has been given.

a. Peak blood levels usually are obtained 1 hour after an intramuscular dose, 30 minutes after the completion of an intravenous infusion, or 1—2 hours after an oral dose. In patients with renal insufficiency who receive antimicrobials by the parenteral route, peak levels may be delayed 2—4 hours after an intramuscular antibiotic dose or 1 hour after an intravenous dose.

b. Trough blood levels are obtained immediately before the next dose is due.

c. The blood should be obtained in tubes free of anticoagulant.

d. The sample should be taken promptly to the laboratory and quickly pro¬cessed. Some antibiotics rapidly lose activity, and the simultaneous pies¬ence of two antibiotics may result in one agent inactivating the other (e.g., carbenicillin can inactivate gentamicin).

e. The laboratory requisition should indicate clearly the antibiotic level de¬sired, time of most recent dose, amount of most recent dose, and any con¬comitant treatment with other antibiotics.

2. Techniques for assay of antibiotic levels. Prior to 1970, bioassays (agar diffu¬sion and broth dilution) were the most commonly used techniques to assay for levels of antibiotics in bodily fluids. l3ioassnys have been largely supplanted by a variety of more accurate and reproducible methods (e.g., immunoassays and high-pressure liquid chromatography),

a. Bioassays are performed by parallel dilution of both antibiotic standards and the patient’s bodily fluid. The dilutions then are tested for their ability to inhibit the growth of an indicator organism. The quantity of antibiotic in the bodily fluid is derived from the relationship between the degree of inhibition of the indicator organism by the bodily fluid and the inhibition by the antibiotic standards. Because bioassays depend on the inhibitory effects of an antibiotic on an organism, they lack specificity (i.e., they cannot differentiate between the effects of two or more antibiotics present in a bodily fluid). Therefore, it is essential to submit complete and accurate information about combination antimicrobial therapy with specimens sent for bioassay. With such information, the laboratory can sometimes circumvent the problem by technical manipulations (e.g., add beta-lacta¬mase to inhibit penicillias, use niultidrug-resistsnt indicator organisms, or remove antibiotics with cation-exchange resins). Most bioassay systems are not as precise as other types of assays but, when the tests are per¬formed carefully with adequate controls, the precision generally is adequate for clinical use.

b. Immunologic assays are presently the most widely used method for de¬termining antibiotic levels in bodily fluids. They exploit the specificity of the antigen-antibody (antimicrobial-antibody) reaction and use sophisticated instrumentation. More simple latex agglutination tests have also been developed and marketed for the semiquantitative assay of aminoglycoside antibiotics. Immunoassays have gained widespread acceptance because they are rapid, accurate, specific, and easier to perform than bioassays. Aminoglycoside and vancomycin levels now are routinely available in many laboratories using the immunoassay method.

c. High-pressure liquid chromatography is a method for separating com¬pounds; quantitation is subsequently achieved by analysis of the separated compounds. Liquid chromatographic procedures have been developed to measure almost all antibiotics in clinical specimens but are used most widely for chloramphenicol because no suitable immunoassay has been developed for this drug. Immunoassays generally are favored because they are simpler to perform.

B. Clinical application. Determination of antibiotic levels may be considered in the following situations:

1. When complicated or life-threatening infections exist secondary to organisms with MIC or MBC values near the maximum achievable levels of the antibiotic being used. Pneumonia and bacteremia due to gram-negative organisms may respond more favorably to treatment when therapeutic plasma levels of amino¬glycosides are achieved [51, 52]. A high peak concentration of aminoglycoside relative to the MIC for the infecting organism has been correlated with im¬proved clinical response to therapy [53J. For further discussion of the role of aminoglycoside levels, see Chap. 28H.

2. When one wishes to monitor therapy with an antibiotic that could have toxic side effects, particularly in the presence of altered hepatic or renal function (e.g., aminoglycosides; see Chap. 28H).

3. When an infection due to a sensitive organism is not responding to antibiotic treatment and all other therapeutic approaches have been optimized.

C. Interpretation. As a general guide, it is anticipated that an infection will respond to therapy if a level of antibiotic greater than the MIC of the infecting organism can be achieved at the site of infection. However, the relationship between achievable serum levels and response at an extravascular site of infection is variable. Also, factors other than an absolute serum level may be important (e.g., magnitude of level in comparison to MIC, duration of level above the MIC, and effect of serum protein binding). Determination of an antibiotic level is not a substitute for clinical judgment, and other therapeutic modalities must always be optimized (e.g., draining abscesses, removing foreign bodies, and bolstering host defense mechanisms).
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Antimicrobial susceptibility testing

Antimicrobial susceptibility testing


Definition: In vitro study of bacterial susceptibility to antibiotics.

Types

1-Disc diffusion tests

Limitation of disc diffusion tests:-

-Not applied to slowly –growing, Fastidious organisms or anaerobes .

-Mycobacterial and fungus susceptibility testing requires specific techniques

- The reported sensitivity tests results not applied to clinical sites infections, e.g –salmonella Typhi to aminoglycosids.

-Not related to the achieved serum levels or body fluid levels of antibiotics.

-Bacteriostatic measures only.

-Can’t be applied to certain antibiotics such as polymyxines.

2,Dilution susceptibility testes:-

(micro) minimal inhibitory and minimal bactericidal activity methods.

Methods

-Broth dilution tests

-Agar dlution method.

Application:-

-Serious infection where endpoint concentration is ended

-Disc diffusion yield inter mediate susceptibility

-Life threatening infection due to organisms with unpredictable susceptibility pattern.

-Fastidious or slowly growing organisms.

-Failure of antibiotic therapy

-Serious infections caused by organisms susceptible only to toxic agents

Limitation

-Difficult

It needs the knowledge about the achievable level in serum or body filmed

3- Automated method

4-Antimicrobial concentration gradient methods

-A serial antibiotic dilations are incorporated into the agar.

-E test
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Policies for prevention of infection to or / and from Health works

1) Tuberculosis : -


- Staff are Mantoux tested and have chest X ray at start of hospital employment .

- Mantoux negative BCG immunization and be sure to convert mantoux negative to positive .

- Mantoux positive Deals with patients with open T.B or samples known to have T.B. bacilli .

- Isolate patient with open T.B in single room until 2-3 weeks after antituberculous therapy .

- Each sputum sample should be handled as if it had T.B and never be opened in the ward .

- In the lab See precautions of handling sputum samples .

2) Viral Hepatitis : -

- Exclude staff with HBsAg positive from renal dialysis units or from carrying exposure – prone procedures

- Precautions should be taken in the lab. To prevent infections to workers .

- All staff with regular contact with blood should have anti HBS with titre > (10 lu/L)

Precautions to prevent viral hepatitis : -

- Isolate the patients (stool / urine / needle isolation)

- Take blood samples with gloves

- Transport to the lab in sealed plastic bags.

- Samples are put in upright position in non leaking screw caps containers

- Samples and requests should be labeled ashepatitis risk .

- Take care of samples from suspected patients .

- Accidental prick to staff should be reported to senior staff , take hyper immune globulin with 24-48 hours and vaccinate if HBS antibodies is negative .

- Wearing of two gloves , waterproof apron and goggles together with many other precautions are necessary when surgery is carried out on patients with hepatitis B. (universal precautions) .

- Staff members positive for HBsAg or e antigen should not work in dialysis unit , oncology , surgery or transplant unit .

3)AIDS :-

- Blood and blood products should be screened for HIV 1/2.

- Universal precautions against blood – borne viruses should be taken when blood or blood staining splashing are anticipated as risk .

- Post exposure drug prophylaxis is recommended for staff sustaining a sharp injury from a patient or HIV .

Policies for Control of Hospital –acquired Infections

Each hospital has many procedures and policies which attempt to reduce the chances of hospital infection occurring , but the extent to which these policies are effectively carried out on a day to a day basis varies greatly between different hospitals or different areas in the hospital .

Procedures for control Include : -

- Sterilization and disinfection of contaminated items .

- Disposal of infected rubbish or linen .

- Aseptic techniques in the operating theatre

- Procedures carried in wards such as changing of wound dressings , urinary catheterization and setting up of an intravenousdrip .

- Protective isolation of infected patients or protective isolation of highly susceptible patients .

- Use of antibiotics therapy according to a greed policy .

- Education of hospital staff in hospital hygiene .

- Good staff health facilities .

- Adequate use of the clinical microbiology for the precise bacteriological diagnosis .

- Control infection committee which helps to design hospital policies and discusses any difficulties encountered during the implementation of these policies .
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Antiseptic solution uses

Phonelics:-


Examples Compounds :-

- clearsol

- Hycolin

- Active against:-

- Gram negative bacteria

- Gram positive bacteria

- Mycobacteria

Little activity :

- endospores.

- viruses br hepatitis B virus.

Effective concentration 2 %

Perochlorites and chlorines

- chloros

- Domestos

- Diversol Bx

- Sterite

- Milton

Active against:-

- Bacteria

- Viruses

Less active against:-

Mycobacteria

For use in virology and for spilled blood :-

The effective concentration 10.000 parts per million for AID, HBs Ag 1000 P.P for cleaning.

Glutaraldehyde ang formaldehyde :-

- Asep.

- Cidex

- Clinicide

- 3 M

- Totacide

- Triocide

Working concentration 2 %

- It is bactericidal and virucidal but less effective against mycobacteria.

- Effective concentration 2 %

Ethyl alcohol:-

Ethanol 70 %

Active against; bacteria and Acid – fast bacilli.

Inactive against spores

Quaternary ammonium compounds

- mpholytes

- isguanides

active against viruses, spores , mycobacteria and a non enveloped viruses.

Guanides:-

-chlorhexidine

activity against staph .aureus, moderate Gram – negative bacilli, less active against Pseudomonas which can grow in chlorhexidine solution.

Iodophors and Iodine:

Active against vegetative bacteria, some sporicidal, some antiviral and antifungal.







Thursday, May 26, 2011

Viral Hepatitis-Old problem revisited

VIRAL HEPATITIS






The term VIRAL HEPATITIS is usually used to describe infections caused by agents whose primary tissue tropism is the liver.

To date, at least five hepatitis viruses have been recognised, and these have been named:-

Hepatitis A, B, C, D and E.

Acute hepatitis may also occur as part of the clinical course of a number of viral infections, including

human cytomegalovirus, Epstein-Barr virus, herpes simplex virus, yellow fever virus and rubella.

Viral hepatitis can be classified according to mode of transmission

ENTERICALLY TRANSMITTED HEPATITIS: A and E

PARENTERALLY TRANSMITTED HEPATITIS B , C , D and G

HEPATITIS A VIRUS

Virology

RNA Picornavirus

o Single serotype worldwide

o Acute disease and asymptomatic infection

· No chronic infection

o Protective antibodies develop in response to infection - confers lifelong immunity

Hepatitis A is caused by HAV, a 27-nm ribonucleic acid (RNA) agent that is classified as a picornavirus. Only one serotype has been observed among HAV isolates collected from various parts of the world. HAV causes both acute disease and asymptomatic infection. HAV does not cause chronic infection. Total antibody to HAV develops in response to infection and confers lifelong immunity from future HAV infection.

Mode of transmission:


Feces can contain up to 108 infectious virions per milliliter and are the primary source of HAV. Viremia occurs during the preclinical and clinical phases of illness, and HAV has been transmitted by transfusion (before screening of blood and blood products for HAV was initiated) and by injection drug use. Virus has also been found in saliva and urine during the incubation period in experimentally infected animals, but transmission by saliva or urine has not been reported to occur.

HEPATITIS A VIRUS TRANSMISSION

· Close personal contact (e.g., household contact, sex contact, child day-care centers)

· Contaminated food, water (e.g., infected food handlers)

· Blood exposure (rare) (e.g., injection drug use, rarely by transfusion)

Transmission of HAV generally occurs when susceptible persons put anything in their mouths that has been contaminated with the feces of an infected person. Close personal contact is the most common mode of HAV transmission, as demonstrated by infections among household and sex contacts of persons with hepatitis A and among children in day-care center outbreaks. Contaminated food and water can also serve as vehicles of HAV transmission. HAV transmission can occur when an infected food handler directly handles uncooked or cooked foods. Outbreaks have also been reported in association with foods contaminated before wholesale distribution, such as fresh vegetables contaminated at the time of harvesting or processing. HAV transmission can occur as a result of blood exposures such as injecting drug use or blood transfusion because viremia can occur prior to the onset of illness in infected persons. Screening of blood products for HAV has essentially eliminated the already extremely low risk associated with transfusion.

Incubation Peroid:

The average incubation period for hepatitis A is 30 days, with a range of 15 to 50 days.

Clinical Picture:

Patients characteristically have abrupt onset of symptoms which can include fever, malaise, anorexia, nausea, abdominal discomfort, dark urine, and jaundice. The severity of clinical disease associated with HAV infection increases with increasing age; jaundice occurs among less than 10% of children younger than 6 years of age, 40%-50% of older children, and 70%-80% of adults.

Complications of hepatitis A include fulminant hepatitis, in which the case fatality rate can be greater than 50% despite medical interventions such as liver transplantation; cholestatic hepatitis, with very high bilirubin levels that can persist for months; and relapsing hepatitis, in which exacerbations can occur weeks to months after apparent recovery. Chronic infection does not occur following HAV infection.





Laboratory Diagnosis Of Hepatitis A

-The diagnosis of acute HAV infection is confirmed during the acute or early convalescent phase of infection by the presence of IgM antibodies to HAV (IgM anti-HAV). IgM anti-HAV is generally present 5-10 days before the onset of symptoms and is no longer detectable in the vast majority of patients 6 months later.

- anti-HAV IgG, which also appears early in the course of infection, remains detectable for the lifetime of the individual and confers lifelong protection against infection. Commercial tests are available for the detection of IgM and total (IgM and IgG) anti-HAV in serum.

-In infected persons, HAV replicates in the liver, is excreted in bile, and is shed in the stool. Peak infectivity occurs during the 2-week period before onset of jaundice or elevation of liver enzymes, when the concentration of virus in stool is highest. The concentration of virus in stool declines after jaundice appears. Children and infants can shed HAV for longer periods than adults, up to several months after the onset of clinical illness. Chronic shedding of HAV in feces does not occur; however, shedding can occur in persons who have relapsing illness. Viremia occurs soon after infection and persists through the period of liver enzyme (alanine aminotransferase [ALT]) elevation.

HAV RNA can be detected in the blood and stool of most persons during the acute phase of infection by using nucleic acid amplification methods, such as PCR, and nucleic acid sequencing has been used to determine the relatedness of HAV isolates. These methods, however, are available in only a limited number of research laboratories and are not used generally for diagnostic purposes.

-Elevated liver function tests begin from 4th weeks of infection and reach maximum elevation in 8th weeks after infection and return to normal within 12th weeks after infection notice that jaundice incidence differs according to age of infection-



· Jaundice by age group: <6 yrs

6-14 yrs

>14 yrs

<10%

40%-50%

70%-80%





PREVENTING HEPATITIS A

· Hygiene (e.g., hand washing)

· Sanitation (e.g., clean water sources)

· Hepatitis A vaccine (pre-exposure)

· Immune globulin (pre- and post-exposure)

Notes:

Good hygienic practices and adequate sanitation are important elements in the prevention of HAV infection, particularly in the developing world. However, hepatitis A vaccine is the key component in the overall strategy to prevent HAV infection in the United States. Immune globulin is also available for pre-exposure and post-exposure prophylaxis.

PREPARATION OF INACTIVATED

HEPATITIS A VACCINES

· Cell culture adapted virus grown in human fibroblasts

· Purified product inactivated with formalin

· Adsorbed to aluminum hydroxide adjuvant



Notes:

In the United States, highly immunogenic and efficacious inactivated hepatitis A vaccines were first licensed in 1995 by the Food and Drug Administration (FDA). These vaccines are prepared by methods similar to those used for inactivated poliovirus vaccine. Cell culture-adapted virus is propagated in human fibroblasts, purified from cell lysates by ultrafiltration and exclusion gel chromatography or other methods, inactivated with formalin, and adsorbed to an aluminum hydroxide adjuvant.

DURATION OF PROTECTION AFTER HEPATITIS A VACCINATION

· Persistence of antibody

o At least 5-8 years among adults and children

· Efficacy

o No cases in vaccinated children at 5-6 years of follow-up

· Mathematical models of antibody decline suggest protective antibody levels persist for at least 20 years

· Other mechanisms, such as cellular memory, may contribute

Notes:

Among adults and children, studies have demonstrated that detectable antibody persists for at least 5-8 years after completing the vaccination series. Although data regarding long-term efficacy are limited, no cases among vaccinated children were observed in one community at 5-6 years of follow-up. Estimates of antibody persistence derived from mathematical models of antibody decline indicate that protective levels of anti-HAV persist for at least 20 years. Whether other mechanisms such as cellular memory also contribute to long-term protection is unknown.

FACTORS ASSOCIATED WITH DECREASED IMMUNOGENICITY TO HEPATITIS A VACCINE

· Decreased antibody concentration:

o Concurrent administration of IG

o Presence of passively-transferred maternal antibody

o Age

o Chronic liver disease

· Decreased seroconversion rate:

o HIV infection

o May be related to degree of

immunosuppression

o Liver transplantation

Notes:

The presence of anti-HAV at the time of vaccination appears to blunt the immune response. Administration of immune globulin (IG) concurrently with the first dose of hepatitis A vaccine did not decrease the proportion of adults who developed protective levels of antibody compared with adults who had been administered hepatitis A vaccine alone, but the geometric mean antibody concentrations (GMCs) among adults who received IG were lower 1 month after completion of the vaccination series than the GMCs of any adults who had been administered hepatitis A vaccine alone. The reduced immunogenicity of hepatitis A vaccine that occurs with concurrent administration of IG does not appear to be clinically significant. IG and hepatitis A vaccine can be given concurrently if indicated.

Reduced vaccine immunogenicity also has been observed in infants who had passively-transferred antibody because of prior maternal HAV infection and were administered hepatitis A vaccine according to a number of different schedules. In most studies, all infants developed protective levels of antibody, but the final GMCs were approximately 1/3 to 1/10 those of infants born to anti-HAV-negative mothers.

Based on limited data, final antibody concentrations might be lower among older vaccinated persons.

Vaccination of adults with chronic liver disease of viral or nonviral etiology produced seroprotection rates similar to those observed in healthy adults. Final antibody concentrations, however, were substantially lower for each group of patients with chronic liver disease than for healthy adults.

Hepatitis B

HBV(DNA) from Hepadna virus

Incubation Peroid:

6 weeks-6 months

Mode Of Transmission:

Parenreral, sexual, vertical

Clinical Course:

Prolonged and more severe than A

Laboratory Diagnosis:

-Elevated ALT,AST from 10-100 folds Acute infection with resolution

-Viralantigens:

1) Surface antigen (HBsAg) is secreted in excess into the blood as 22 nm spheres and tubules. Its presence in serum indicates that virus replication is occurring in the liver

2) 'e' antigen (HBeAg) secreted protein is shed in small amounts into the blood. Its presence in serum indicates that a high level of viral replication is occurring in the liver

3) core antigen (HBcAg) core protein is not found in blood

-Antibody response:

1) Surface antibody (anti-HBs) becomes detectable late in convalescence, and indicates immunity following infection. It remains detectable for life and is not found in chronic carriers (see below).

2) e antibody (anti-HBe) becomes detectable as viral replication falls. It indicates low infectivity in a carrier.

3) Core IgM rises early in infection and indicates recent infection

4) Core IgG rises soon after IgM, and remains present for life in both chronic carriers as well as those who clear the infection. Its presence indicates exposure to HBV.



Figure: Acute Hepatitis B Infection

Chronic hepatitis B

Persistance of surface antigen and prolonged persistence of e antigen.



Figure: Chronic Hepatitis B Infection



Hepatitis C Virus:

HCV(RNA) from Togavirus related to the Flavi and Pesti viruses.

Features of Hepatitis C Virus Infection



Incubation period Average 6-7 weeks

Range 2-26 weeks

Acute illness (jaundice) Mild (≤20%)

Case fatality rate Low

Chronic infection* 60%-85%

Chronic hepatitis* 10%-70% (most asx)

Cirrhosis* <5%-20%

Mortality from CLD 1%-5%



*Age related



Exposures Known to be Associated With HCV Infection

· Injecting drug use

· Transfusion, transplant from infected donor

· Occupational exposure to blood

- Mostly needle sticks

- Case reports of transmission from blood splash to eye; one from exposure to non-intact skin

-Prevalence 1-2% among health care workers

Lower than adults in the general population

10 times lower than for HBV infection

· Iatrogenic (unsafe injections)

· Birth to HCV-infected mother

Average rate of infection 4%

Higher (19%) if woman co-infected with HIV

Role of viral titer unclear

No association with

Delivery method

Breastfeeding

Infected infants do well

Severe hepatitis is rare

Sex with infected partner

· Household Transmission of HCV

· Rare but not absent

· Could occur through percutaneous/mucosal exposures to blood

o Contaminated equipment used for home therapies

§ IV therapy, injections

o Theoretically through sharing of contaminated personal articles (razors, toothbrushes)



Laboratory Diagnosis Of Hepatitis C:

-Mild elevation of ALT,AST

-With fluctuation in AST(surrogate Marker of chronic hepatitis C).

1) Serology

.

1-HCV-specific IgG indicates exposure, not infectivity

2) PCR detects viral genome in patient's serum

3) Quantitative PCR to detect viral load response to therapy



                                                    Hepatitis D



HDV is a defective single-stranded RNA virus that requires the helper function of HBV to replicate. HDV requires HBV for synthesis of envelope protein composed of HBsAg, which is used to encapsulate the HDV genome.



Hepatitis D - Clinical Features

· Coinfection

o severe acute disease

o low risk of chronic infection

· Superinfection

o usually develop chronic HDV infection high

o risk of severe chronic liver disease

Notes:

HDV infection can be acquired either as a co-infection with HBV or as a superinfection of persons with chronic HBV infection. Persons with HBV-HDV co-infection may have more severe acute disease and a higher risk of fulminant hepatitis (2%-20%) compared with those infected with HBV alone; however, chronic HBV infection appears to occur less frequently in persons with HBV-HDV co-infection. Chronic HBV carriers who acquire HDV superinfection usually develop chronic HDV infection. In long-term studies of chronic HBV carriers with HDV superinfection, 70%-80% have developed evidence of chronic liver diseases with cirrhosis compared with 15%-30% of patients with chronic HBV infection alone.

Hepatitis D Virus Modes of Transmission

· Percutanous exposures

o injecting drug use

· Permucosal

o exposures sex contact

Notes:

The modes of HDV transmission are similar to those for HBV, with percutaneous exposures the most efficient. Sexual transmission of HDV is less efficient than for HBV. Perinatal HDV transmission is rare.



The serologic course of HDV infection varies depending on whether the virus is acquired as a co-infection with HBV or as a superinfection of a person with chronic HBV infection.

In most persons with HBV-HDV co-infection, both IgM antibody to HDV (anti-HDV) and IgG anti-HDV are detectable during the course of infection.

However, in about 15% of patients the only evidence of HDV infection may be the detection of either IgM anti-HDV alone during the early acute period of illness or IgG anti-HDV alone during convalescence.

Anti-HDV generally declines to sub-detectable levels after the infection resolves and there is no serologic marker that persists to indicate that the patient was ever infected with HDV. Hepatitis Delta antigen (HDAg) can be detected in serum in only about 25% of patients with HBV-HDV co-infection. When HDAg is detectable it generally disappears as HBsAg disappears and most patients do not develop chronic infection. Tests for IgG anti-HDV are commercially available in the United States. Tests for IgM anti-HDV, HDAg and HDV RNA by PCR are only available in research laboratories.







In patients with chronic HBV infection who are super-infected with HDV several characteristic serologic features generally occur, including: 1) the titer of HBsAg declines at the time HDAg appears in the serum, 2) HDAg and HDV RNA remain detectable in the serum because chronic HDV infection generally occurs in most patients with HDV superinfection, unlike the case with co-infection, 3) high titers of both IgM and IgG anti-HDV are detectable, which persist indefinitely.

Hepatitis E

Recently identified cause of enterically transmitted non-A, non-B (NANB) hepatitis

ClinicalFeatures

Incubation period 30-40 days

Acute, self limiting hepatitis, no chronic carrier state

Age: predominantly young adults, 15-40 years

Complications

Fulminant hepatitis in pregnant women. Mortality rate is high (up to 40%).

Virus cannot be cultured in vitro.

1) Calicivirus-like particles in the stool, by electron microscopy

2)Specific IgM in serum

3) PCR HEV-specific sequences in stool

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Hospital – acquired Infection

Hospital – acquired Infection


Definition :

It is infection acquired while staying in hospital . It meets the following criteria :-

Not found on admission .

Temporally associated with admission or a procedure at a health care facility .

It was not incubating at admission and may be related to a previous procedure or admission to same or other health care – facility e.g HIV acquired from previous blood transfusion .



Routes of infection : -

Self infection (auto genous infection) .

Cross – infection .

Environmental infection

-Dust.

-Bed linen

-Air .

-Moist solutions may be contaminated Pseudomonas

Klebsiella

Factors which promote hospital acquired infection : -

Impaired general host defencas of the patient .

Impaired local host defences of the patient .e.g injury of skin barrier .

Presence of hospital pathogen which are endemic epidermidis . Increasing problem is associated with MRSA strepto . pneumonia is the next common gram positive assoiated with lower respiratory tract infection .

Types of hospital infection : -

The three most frequent types : -

Urinary tract infection .

Wound infection .

Lower respiratory tract infection .

Other types of less common infections : -

Bed sores and varicose ulcer infection

Alimentary tract infection .

All severe bacterial infections lead to septicaemia .

Organisms causing Hospital acquired infection : -

In many hospital but also each hospital has specific endemic or epidemic strains of particular types of organism in certain areas .

In hospitals with large specific units e.g oncology , special care baby units opportunists organisms as well as the common pathogens are likely to cause problem

Pathogens causing hospital acquired infections include

Conventional pathogen e.g strepto-pyogenes .

Conditional pathogen e.g Bacteroides .

Opportunists pathogen e.gPneumocystis carinii .

The most common organisms are staph. aureus and staph.epidermidis

-Gram Negative bacilli such as : -

E.coli is the most prequent single bacterial species associated with hospital acquired infection .

klebsiella , proteus species and Pseudomonas are also common cause .

- Fungal and viral infection are only ocassionaly acquired in hospital .

- Protozoa are rare .

Laboratory diagnosis Of Hospital – acquired Infections :

Samples collected from the patient includes Blood culture , sputum, tracheostomy wound swabs and other samples. Perform cultured before antibiotics therapies and judged accurately if the isolate is just contamination or already a true pathogen .

Samples from the environment includes all equipments in the ICU and from antiseptic solutions according to the place of environmental assay.

Typing of the isolated organisms from both patients, environment and personnel by the following typing methods :

Bio typing

Sero typing

Phage typing

Bacteriocine typing

DNA finger printing



1- Hospital – acquired urinary tract infections

The most common type of hospital infection (about 25%)

The source auto- genous from patient's own faecal flora or from the environment (urinals , wash bowl) .

Colonization of the patient's large intestine by hospital resistant strains of Gram – negative bacilli occurs when the patient stays in hospital more than few days or when patient take antibiotics .

E.coli is the most common pathogen especially resistant strains to sulfonamides and ampicillin other pathogens such as klebsiella aerogenes, Enterococcus spp. (Vancomycin resistant) and Pseudomonas are common .

Ocassionally candida and serratia marscenes may cause such infection .

Patients with impaired immune system may become infected wit T.B and Nocardia asteroids , salmonella spp. Or Papoviruses .

Mixed infections are common with catheterization

Effects of UII : -

Asymptomatic infection .

Symptomatic infection

Prologed hospital stay .

Pyelonephritis , haemorrhage after operation

Septicaemic shock .

Catheterization hazards : -

Patients with catheter have the following dangers:

10-30% develop UTI by the fifth day .

100% develop UTI by 2-3 weeks .

Prevention of catheter – associated urinary infection : -

Good aseptic technique to the surrounding

area with chlorhxidine solution and cream .

Never touch the tip of the catheter .

Wash hands with chlor hexidine solution .

Chlorhexidine installation into the bladder .

Early removal of the catheter .

Change it within few days or when dirty .

-Take care not to soil the hands of the staff .

4) Policies for control of hospital acquired urinary tract infections :

This depends upon the extent to which these policies are effectively carried from day to day .

Isolate patients with multiple antibiotic resistant strains .

Sponge with antiseptic solution should be put between catheter and urethra especially in females.

Repeated self catheterization with use of antiseptic solution is preferred in paraplegic patient .

2-Surgical wound Infection

1) The type of the wound is the most single factor associated with the development of wound infection . The major types of surgical wounds can be classified as follows : -

-Clean operation wounds in area not involve regions of gastrointestinal tract, respiratory tract or genitourinary tract. It is associated with very low rates of infection 2-5%.

- Contaminated operation Surgery that involves a site with known normal flora (apart from skin) e.g operation on colon , gall bladder , mouth or vagina .

- Infected operation wounds , the operation site may be infected at time of surgery e.g incision of an abscess .

2) Surgical team:

- Skill of surgeon

- Good aseptic techniques

- Carriage of staph. aureus .

3) Age and general condition of the patient .

Persistence of local structural abnormal .

Ward factors post operatively

Complication of wound Infections : -

Delayed wound healing

Failure of graft .

Infections of bones , joints , peritoneal cavity .

Septiceamia

Types of hospital acquired wound infections include : -

Ward infection

Theatre infection

(How to differentiate ?)

Prevention of theatre infection : -

Protective of theatre clothing .

Gloves for the hands after chlorhexidine antiseptic solution

Movements of staff should be reduced to a minimum .

Very clean theatre with good managing of the air direction around the operative table .

Disifect the skin of the patient and many use preoperative baths with hexachlorophene or chlorhexidine detergents .

Prevention of wards infections : -

Isolation rooms for wards should be available for patients infected with MRSA or with severe wound infections especially in high risk surgery e.g cardio thoracic orthopaedic , neuro surgical units and ICU .

Adequate non touch technique for dressing of the wound .

Suitable bad spacing between patients (2.5m)todecrease air or dust spread .

The patient should be admitted for the shortest time before the operation to decrease the chances of colonization or infection with hospital strains .

Restrict the use of prophylactic antibiotics .

Exclude patients with skin disease from the word .

Exclude members of staff with boils , abscess or other infected skin lesions .

If an out breaks occur , how to control ?

Be sure that it is cause by the same epidemic strain with similar antibiotic resistance pattern and phage type .

Isolate the patient .

The medical staff shown to be carrier should temporarily cease the work and use chlorhexidine on the affected area with all hygiene measure .

Close the ward in severe cases .

Use vancomycin for therapy .

3-Acute Lower Respiratory tract Infection

Third most common infection in hospital acquired infection

Patients predisposed are usually paediatric patients or elderly patients with predisposing chest conditions .

Causative pathogens include , strepto . pneumoniae , staph. aureus , influenza A or B , respiratory syncytial virus and legionella species.



Infections in ICU



It is very common to find high rates of infections in intensive care units.

Samples collected from the patient includes Blood culture , sputum, tracheostomy wound swabs and other samples. Perform cultured before antibiotics therapies and judged accurately if the isolate is just contamination or already a true pathogen .

Samples from the environment includes all equipments in the ICU and from antiseptic solutions .

Preventive measures are the same as before and the measures for the equipments include : -

Adequate cleaning of the equipment in between patients

Heating water in the ventilator to 50oC every day .

Use of autoclavable ventilator or decontaminate it with ethylene or formaldehyde gas .

Anaesthetic bags , suction apparatus , face masks may be efficiently cleaned with washing machine or by low temperature disinfectant .

Infective hazards of intravenous fluid

Between 0.2 – 8% of patients receiving intravenous fluid develop septicaemia and may develop endotoxic shock if gram – negative bacilli multiply at the additive solution added to the fluid .

Causative organisms : -

Gram negative bacilli contaminating fluid solutions .

Bacterial orviral contamination of blood and blood products including HIV , HTLVI , hepatitis viruses , Epestein Barr virus , CMV , Treponema pallidam and malarial parasites .

Prevention of infections with Fluid Infusion.

Perfect antiseptic technique to the skin over the area used with shaving of the excess hair and palpate the vein before use of antiseptic solurtion (chlorohexidine or iodine)

Place the needle in the place and needs to be anchored securely as excessive movement predisposes to site infection

Topical Betadine antiseptic solution and if needed antifungal cream may be added .

Inspect the site of the drip , if infected with draw the complete set immediately and insert it at different site .

Change the complete set every 24-48h

Restrict the use of antibiotic therapy

Diagnosis of infections associated with intravenous infusion therapy : -

With draw blood samples for blood culture .

Send the bottle , cannula and there catheter to the microbiological lab.

Inspect the bottle for presence of defects , and with draw fluid for microscopic examination , culture at 35oC , 4oC and at room temperature .

Culture the catheter tip or cannula on broth or by rolling moistend cannula on surface of blood agar plate – organisms isolated include staph. epidermidis , staph. aureus , candida albicans , klebsiella species , serratia , pseudomonas aeruginosa .

Begins blind therapy with cloxacillin plus gentamicin .





Policies for prevention of infection to or / and from Health works

1) Tuberculosis : -

Staff are Mantoux tested and have chest X ray at start of hospital employment .

Mantoux negative BCG immunization and be sure to convert mantoux negative to positive .

Mantoux positive Deals with patients with open T.B or samples known to have T.B. bacilli .

Isolate patient with open T.B in single room until 2-3 weeks after antituberculous therapy .

Each sputum sample should be handled as if it had T.B and never be opened in the ward .

In the lab See precautions of handling sputum samples .

2) Viral Hepatitis :

Exclude staff with HBsAg positive from renal dialysis units or from carrying exposure – prone procedures

Precautions should be taken in the lab. To prevent infections to workers .

All staff with regular contact with blood should have anti HBS with titre > (10 lu/L)

Precautions to prevent viral hepatitis : -

Isolate the patients (stool / urine / needle isolation)

Take blood samples with gloves

Transport to the lab in sealed plastic bags.

Samples are put in upright position in non leaking screw caps containers

Samples and requests should be labeled ashepatitis risk .

Take care of samples from suspected patients .

Accidental prick to staff should be reported to senior staff , take hyper immune globulin with 24-48 hours and vaccinate if HBS antibodies is negative .

Wearing of two gloves , waterproof apron and goggles together with many other precautions are necessary when surgery is carried out on patients with hepatitis B. (universal precautions) .

Staff members positive for HBsAg or e antigen should not work in dialysis unit , oncology , surgery or transplant unit .

3)AIDS :

Blood and blood products should be screened for HIV 1/2.

Universal precautions against blood – borne viruses should be taken when blood or blood staining splashing are anticipated as risk .

Post exposure drug prophylaxis is recommended for staff sustaining a sharp injury from a patient or HIV .

Policies for Control of Hospital –acquired Infections

Each hospital has many procedures and policies which attempt to reduce the chances of hospital infection occurring , but the extent to which these policies are effectively carried out on a day to a day basis varies greatly between different hospitals or different areas in the hospital .

Procedures for control Include : -

Sterilization and disinfection of contaminated items .

Disposal of infected rubbish or linen .

Aseptic techniques in the operating theatre

Procedures carried in wards such as changing of wound dressings , urinary catheterization and setting up of an intravenousdrip .

Protective isolation of infected patients or protective isolation of highly susceptible patients .

Use of antibiotics therapy according to a greed policy .

Education of hospital staff in hospital hygiene .

Good staff health facilities .

Adequate use of the clinical microbiology for the precise bacteriological diagnosis .

Control infection committee which helps to design hospital policies and discusses any difficulties encountered during the implementation of these policies .





Lectures on applied clinical microbiology [Kindle Edition]- B004Y0XF54

Lectures on applied clinical microbiology [Kindle Edition]ASIN: B004Y0XF54


Completely updated and in full color, book covers the base lines of diagnostic microbiology. A logical building-block approach supplies what students need to know in an easy-to-use, memorable format. Material is presented in a progressive manner, from basic principles and concepts to systematic identification of etiologic agents of infectious diseases, promoting greater understanding and the development of laboratory skills. The first chapter of the book explains basic principles and concepts, setting up a firm foundation of diagnostic microbiology. It summarizes the role of clinical microbiologists and technical jobs of junior and senior staff. It gives a good idea how to collect good microbiological samples for laboratory diagnosis. Building on these basics, Part II highlights simple culture methods for the identification of significant isolates. Further discussion will be carried out for clinical microbiology approach for diagnosis of organ systems infections with detailed discussion of the laboratory diagnosis of infectious diseases with a focus on the most medically significant and commonly encountered diseases.


Laboratory diagnosis of infectious diseases include bacterial pathogens such as Enterobacteriaceae -- Nonfermentative gram-negative bacilli -- Curved gram-negative bacilli and oxidase-positive fermenters: campylobacters and vibrionaceae -- Haemophilus -- Miscellaneous fastidious gram-negative bacilli -- Neisseria species and Moraxella catarrhalis -- Staphylococci and related organisms -- Streptococci and Streptococcus-like bacteria -- Aerobic gram-positive bacilli -- Anaerobic bacteria -- Antimicrobial susceptibility testing -- Mycobacteria -- Spirochetal infections -- Mycoplasmas and ureaplasmas -- Mycology -- Virology -- Conventional and new and technologies for rapid organisms identification and detection methods. There is also a simple approach for biosafety and biohazard in clinical microbiology laboratories and quality control procedures.


Wednesday, May 25, 2011

Food borne Pathogens: Microbiology and Molecular Biology

The following topics will covered by the Lecture


 Pathogens well established as food borne pathogens.

 Viable but Nonculturable Bacteria in Food Environments

 Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

-Microbiological methods for detection of food borne pathogens:

 Traditional methods

 Recent Methods.



The followings are well established as food borne pathogens

 Bacteria

Yersinia enterocolitica

-Vibrio spp.

-Staphylococcus aureus

- Campylobacter Infections.

-Listeria monocytogenes

-Salmonella spp.

-Shigella spp.

-Escherichia coli

-Clostridium botulinum and Clostridium perfringens -Bacillus cereus



Viruses

 hepatitis A virus,

 rotavirus, astrovirus,

 enteric adenovirus,

 hepatitis E virus,

 human caliciviruses consisting of the noroviruses and the --Sapporo viruses



Food-and Waterborne Protozoan Parasites

 Entamoeba species

 Giardia

In addition to Foodborne Mycotoxins: Chemistry, Biology, Ecology, and Toxicology



Yersinia enterocolitica

 Yersinia enterocolitica includes well-established pathogens and environmental strains that are ubiquitous in terrestrial and fresh water ecosystems

 . Evidence from large outbreaks of yersiniosis and from epidemiological studies of sporadic cases has shown that Y. enterocolitica is a food borne pathogen, and that in many cases pork is implicated as the source of infection.



 The pig is the only animal consumed by man that regularly harbours pathogenic Y. enterocolitica

 . An important property of the bacterium is its ability to multiply at temperatures near to 0ƒC, and therefore in many chilled foods

 . The pathogenic serovars (mainly O:3, O:5,27, O:8 and O:9) show different geographical distribution

 The appearance of strains of serovars O:3 and O:9 in Europe, Japan in the 1970s, and in North America by the end of the 1980s, is an example of a global pandemic.

 The possible risk of reactive arthritis following infection with Y. enterocolitica has led to further attention being paid to this microbe



Vibrio spp

 Vibrio species are prevalent in estuarine and marine environments and seven species can cause seafood borne infections

 Vibrio cholerae O1 and O139 serovtypes produce cholera toxin and are agents of cholera. However, fecal-oral route infections in the terrestrial environment are responsible for epidemic cholera.

 V. cholerae non-O1/O139 strains may cause gastroenteritis through production of known toxins or unknown mechanism



 Vibrio parahaemolytitucs strains capable of producing thermostable direct hemolysin (TDH) and/or TDH-related hemolysin are most important cause of gastroenteritis associated with seafood consumption

 Vibrio vulnificus is responsible for seafoodborne primary septicemia and its infectivity depends primarily on the risk factors of the host.



 V. vulnificus infection has the highest case fatality rate (50%) of any food borne pathogen

 Four other species (Vibrio mimicus, Vibrio hollisae, Vibrio fluvialis, and Vibrio furnissii) that have potential to cause gastroenteritis have been reported

 Some strains of these species produce known toxins but the pathogenic mechanism is largely not understood



Staphylococcus aureus

 Staphylococcus aureus is a common cause of confirmed bacterial foodborne disease worldwide

 Food poisoning episodes are characterized by symptoms of vomiting and diarrhea that occur shortly after ingestion of S. aureus-contaminated food.

 The symptoms arise from ingestion of preformed enterotoxin, which accounts for the short incubation time.



 Staphylococcal enterotoxins are a family of sequence similar, but serologically distinct proteins

 . These proteins have the additional property of being superantigens and, as such, have adverse effects on the immune system

 The enterotoxin genes are accessory genetic elements in S. aureus, meaning that not all strains of this organism are enterotoxin-producing.



 The enterotoxin genes are found on prophage, plasmids, and pathogenicity islands in different strains of Expression of the enterotoxin genes is often under the control of global virulence gene regulatory systems S. aureus.

 Although much progress has been made recently in defining enterotoxin structure and superantigenicity properties, much remains to be learned regarding the binding of enterotoxins to receptors in the gastrointestinal tract and how toxin production leads to the symptoms associated with staphylococcal food poisoning.



Campylobacter Infections

 Campylobacter spp., primarily C. jejuni subsp. jejuni is one of the major causes of bacterial gastroenteritis in the U.S. and worldwide.

 Campylobacter infection is primarily a foodborne illness, usually without complications; however, serious sequelae such as Guillain-Barre Syndrome occur in a small subset of infected patients



 Detection of C. jejuni in clinical samples is readily accomplished by culture and non-culture methods, although improvements in diagnostic approaches are needed

 A significant body of knowledge exists on the epidemiology of Campylobacter infections; however, much less is known about the mechanism of disease, despite over 2 decades of research.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Salmonella spp

The second half of the 20th century saw the emergence of Salmonella serotypes that became associated with new food sources (i.e. chicken eggs) and the emergence of Salmonella serotypes with resistance against multiple antibiotics.



Shigella spp

 Shigella species are members of the family Enterobacteriacae and are Gram negative, non-motile rods

 Four subgroups exist based on O-antigen structure and biochemical properties; S. dysenteriae (subgroup A), S. flexneri (subgroup B), S. boydii (subgroup C) and S. sonnei (subgroup D).

 Clinical manifestations include mild to severe diarrhea with or without blood, fever, tenesmus, and abdominal pain.

 Further complications of the disease may be seizures, toxic megacolon, reactive arthritis and hemolytic uremic syndrome

 . Transmission of the pathogen is by the fecal-oral route, commonly through food and water

 The infectious dose ranges from 10-100 organisms. Shigella spp. have a sophisticated pathogenic mechanism to invade colonic epithelial cells of the host, man and higher primates, and the ability to multiply intracellularly and spread from cell to adjacent cell via actin polymerization



Diarrhea-inducing Escherichia coli

 For many years, E. coli was considered a commensal of human and animal intestinal tracts with low virulence potential.

 Today, it is well known that many strains of E. coli act as pathogens inducing serious gastrointestinal diseases and even death in humans.



 There are six major categories of E. coli strains that cause enteric diseases in humans including the

 (1) enterohemorrhagic E. coli, which cause hemorrhagic colitis and hemolytic uremic syndrome (2) enterotoxigenic E. coli, which induce traveler's diarrhea

 (3) enteropathogenic E. coli, which cause a persistent diarrhea in children living in developing countries

 (4) enteroaggregative E. coli, which provoke diarrhea in children

 (5) enteroinvasive E. coli that are biochemically and genetically related to Shigella species and can induce diarrhea

 (6) diffusely adherent E. coli, which cause diarrhea and are distinguished by a characteristic type of adherence to mammalian cells.



Clostridium botulinum and Clostridium perfringens

 Clostridium botulinum produces extremely potent neurotoxins that result in the severe neuroparalytic disease, botulism

 Although of lower lethality, the enterotoxin produced by C. perfringens, during sporulation of vegetative cells in the host intestine, still results in debilitating acute diarrhea and abdominal pain.

 Sales of refrigerated, processed foods of extended durability including sous-vide foods, chilled ready-to-eat meals, and cook-chill foods have increased over recent years



 As a result of conditions accommodating growth, anaerobic spore-formers have been identified as the primary microbiological concerns in these foods

 . Heightened awareness over intentional food source tampering with botulinum neurotoxin has arisen with respect to genes encoding the toxins that are capable of transfer to nontoxigenic clostridia

 Similarly, enterotoxin produced by C. perfringens and the genomic location of the cpe gene has epidemiologic significance for understanding the capability to cause foodborne disease in humans

 The susceptibility of these bacterial spore-formers to physical and chemical agents is examined as well as recommended control measures

 This information is useful in developing molecular strategies to study virulence genes and their regulation as a means to safer foods.



Bacillus cereus

 The Bacillus cereus group comprises six members: B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis and B. weihenstephanensis

 . These species are closely related and should be placed within one species, except for B. anthracis that possesses specific large virulence plasmids

 . . B. cereus is a normal soil inhabitant and is frequently isolated from a variety of foods, including vegetables, dairy products and meat.



 . It causes an emetic or a diarrhea type of food-associated illness that is becoming increasingly important in the industrialized world

 . Some patients may experience both types of illness simultaneously. The diarrhoeal type of illness is most prevalent in the western hemisphere, whereas the emetic type is most prevalent in Japan.

 Desserts, meat dishes, and dairy products are the foods most frequently associated with diarrhoeal illness, whereas rice and pasta are the most common vehicles of emetic illness



 The emetic toxin (cereulide) has been isolated and characterized; it is a small ring peptide synthesised non-ribosomally by a peptide synthetase.

 Three types of B. cereus enterotoxins involved in foodborne outbreaks have been identified.

 Two of these enterotoxins are three-component proteins and are related, while the last is a one-component protein (CytK).



 )Deaths have been recorded both by strains that produce the emetic toxin and by a strain producing only CytK

 Some strains of the B. cereus group are able to grow at refrigeration temperatures

 . These variants raise concern about the safety of cooked, refrigerated foods with an extended shelf life. B. cereus spores adhere to many surfaces and survive normal washing and disinfection (except for hypochlorite and UVC) procedures



Food- and Waterborne Enteric Viruses

 Food- and waterborne viruses contribute to a substantial number of illnesses throughout the world. Among those most commonly known are hepatitis A virus, rotavirus, astrovirus, enteric adenovirus, hepatitis E virus, and the human caliciviruses consisting of the noroviruses and the Sapporo viruses

 . they are transmitted by the fecal-oral route, often by ingestion of contaminated food and water



Food-and Waterborne Protozoan Parasites

 Protozoan parasites have been associated with food and waterborne outbreaks causing illness in humans. Although parasites are more commonly found in developing countries, developed countries have also experienced several foodborne outbreaks. Contaminants may be inadvertently introduced to the foods by inadequate handling practices, either on the farm or during processing of ready-to-eat foods. In some instances, this contamination occurred in endemic regions and is carried to non-endemic areas where an outbreak is initiated. Other protozoan parasites can be found worldwide, either infecting wild animals or in an environment such as water and eventually finding its way to crops grown for human consumption. Parasites can infect immunocompetent individuals, however the clinical presentation can be much more severe and prolonged in immunocompromissed individuals.



Viable but Non culturable Bacteria in Food Environments

 Cells in the viable but non culturable (VBNC) state are alive, but undetectable by routine microbiological methods.

 The presence of such cells in foods presents a special concern, especially when they are human pathogens.

 Biology of the VBNC state and the factors which induce it, the food borne pathogens that are known to enter this state, how cells resuscitate back to the actively growing state, and the importance of the VBNC state in food microbiology are in need for study



Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

 Traditional microbiological methods for testing foods for the presence of pathogens rely on

 -Growth in culture media, followed by isolation, and biochemical and serological identification.

 Traditional methods are laborious and time consuming, requiring a few days to a week or longer to complete. Rapid detection of pathogens in food is essential for ensuring the safety of food for consumers, and in the past 25 years, advances in biotechnology have resulted in the development of rapid methods that reduce the analysis time.



Two major categories of rapid methods include

 - Immunologic or antibody-based assays

 -Genetic-based assays such as the polymerase chain reaction.

 -Generation assays under development include biosensors and DNA chips that potentially have the capability for near real-time and on-line monitoring for multiple pathogens in foods



-Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.



Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.



Food borne Pathogens: Microbiology and Molecular Biology

The following topics will covered by the Lecture


 Pathogens well established as food borne pathogens.

 Viable but Nonculturable Bacteria in Food Environments

 Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

-Microbiological methods for detection of food borne pathogens:

 Traditional methods

 Recent Methods.



The followings are well established as food borne pathogens

 Bacteria

Yersinia enterocolitica

-Vibrio spp.

-Staphylococcus aureus

- Campylobacter Infections.

-Listeria monocytogenes

-Salmonella spp.

-Shigella spp.

-Escherichia coli

-Clostridium botulinum and Clostridium perfringens -Bacillus cereus



Viruses

 hepatitis A virus,

 rotavirus, astrovirus,

 enteric adenovirus,

 hepatitis E virus,

 human caliciviruses consisting of the noroviruses and the --Sapporo viruses



Food-and Waterborne Protozoan Parasites

 Entamoeba species

 Giardia

In addition to Foodborne Mycotoxins: Chemistry, Biology, Ecology, and Toxicology



Yersinia enterocolitica

 Yersinia enterocolitica includes well-established pathogens and environmental strains that are ubiquitous in terrestrial and fresh water ecosystems

 . Evidence from large outbreaks of yersiniosis and from epidemiological studies of sporadic cases has shown that Y. enterocolitica is a food borne pathogen, and that in many cases pork is implicated as the source of infection.



 The pig is the only animal consumed by man that regularly harbours pathogenic Y. enterocolitica

 . An important property of the bacterium is its ability to multiply at temperatures near to 0ƒC, and therefore in many chilled foods

 . The pathogenic serovars (mainly O:3, O:5,27, O:8 and O:9) show different geographical distribution

 The appearance of strains of serovars O:3 and O:9 in Europe, Japan in the 1970s, and in North America by the end of the 1980s, is an example of a global pandemic.

 The possible risk of reactive arthritis following infection with Y. enterocolitica has led to further attention being paid to this microbe



Vibrio spp

 Vibrio species are prevalent in estuarine and marine environments and seven species can cause seafood borne infections

 Vibrio cholerae O1 and O139 serovtypes produce cholera toxin and are agents of cholera. However, fecal-oral route infections in the terrestrial environment are responsible for epidemic cholera.

 V. cholerae non-O1/O139 strains may cause gastroenteritis through production of known toxins or unknown mechanism



 Vibrio parahaemolytitucs strains capable of producing thermostable direct hemolysin (TDH) and/or TDH-related hemolysin are most important cause of gastroenteritis associated with seafood consumption

 Vibrio vulnificus is responsible for seafoodborne primary septicemia and its infectivity depends primarily on the risk factors of the host.



 V. vulnificus infection has the highest case fatality rate (50%) of any food borne pathogen

 Four other species (Vibrio mimicus, Vibrio hollisae, Vibrio fluvialis, and Vibrio furnissii) that have potential to cause gastroenteritis have been reported

 Some strains of these species produce known toxins but the pathogenic mechanism is largely not understood



Staphylococcus aureus

 Staphylococcus aureus is a common cause of confirmed bacterial foodborne disease worldwide

 Food poisoning episodes are characterized by symptoms of vomiting and diarrhea that occur shortly after ingestion of S. aureus-contaminated food.

 The symptoms arise from ingestion of preformed enterotoxin, which accounts for the short incubation time.



 Staphylococcal enterotoxins are a family of sequence similar, but serologically distinct proteins

 . These proteins have the additional property of being superantigens and, as such, have adverse effects on the immune system

 The enterotoxin genes are accessory genetic elements in S. aureus, meaning that not all strains of this organism are enterotoxin-producing.



 The enterotoxin genes are found on prophage, plasmids, and pathogenicity islands in different strains of Expression of the enterotoxin genes is often under the control of global virulence gene regulatory systems S. aureus.

 Although much progress has been made recently in defining enterotoxin structure and superantigenicity properties, much remains to be learned regarding the binding of enterotoxins to receptors in the gastrointestinal tract and how toxin production leads to the symptoms associated with staphylococcal food poisoning.



Campylobacter Infections

 Campylobacter spp., primarily C. jejuni subsp. jejuni is one of the major causes of bacterial gastroenteritis in the U.S. and worldwide.

 Campylobacter infection is primarily a foodborne illness, usually without complications; however, serious sequelae such as Guillain-Barre Syndrome occur in a small subset of infected patients



 Detection of C. jejuni in clinical samples is readily accomplished by culture and non-culture methods, although improvements in diagnostic approaches are needed

 A significant body of knowledge exists on the epidemiology of Campylobacter infections; however, much less is known about the mechanism of disease, despite over 2 decades of research.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Salmonella spp

The second half of the 20th century saw the emergence of Salmonella serotypes that became associated with new food sources (i.e. chicken eggs) and the emergence of Salmonella serotypes with resistance against multiple antibiotics.



Shigella spp

 Shigella species are members of the family Enterobacteriacae and are Gram negative, non-motile rods

 Four subgroups exist based on O-antigen structure and biochemical properties; S. dysenteriae (subgroup A), S. flexneri (subgroup B), S. boydii (subgroup C) and S. sonnei (subgroup D).

 Clinical manifestations include mild to severe diarrhea with or without blood, fever, tenesmus, and abdominal pain.

 Further complications of the disease may be seizures, toxic megacolon, reactive arthritis and hemolytic uremic syndrome

 . Transmission of the pathogen is by the fecal-oral route, commonly through food and water

 The infectious dose ranges from 10-100 organisms. Shigella spp. have a sophisticated pathogenic mechanism to invade colonic epithelial cells of the host, man and higher primates, and the ability to multiply intracellularly and spread from cell to adjacent cell via actin polymerization



Diarrhea-inducing Escherichia coli

 For many years, E. coli was considered a commensal of human and animal intestinal tracts with low virulence potential.

 Today, it is well known that many strains of E. coli act as pathogens inducing serious gastrointestinal diseases and even death in humans.



 There are six major categories of E. coli strains that cause enteric diseases in humans including the

 (1) enterohemorrhagic E. coli, which cause hemorrhagic colitis and hemolytic uremic syndrome (2) enterotoxigenic E. coli, which induce traveler's diarrhea

 (3) enteropathogenic E. coli, which cause a persistent diarrhea in children living in developing countries

 (4) enteroaggregative E. coli, which provoke diarrhea in children

 (5) enteroinvasive E. coli that are biochemically and genetically related to Shigella species and can induce diarrhea

 (6) diffusely adherent E. coli, which cause diarrhea and are distinguished by a characteristic type of adherence to mammalian cells.



Clostridium botulinum and Clostridium perfringens

 Clostridium botulinum produces extremely potent neurotoxins that result in the severe neuroparalytic disease, botulism

 Although of lower lethality, the enterotoxin produced by C. perfringens, during sporulation of vegetative cells in the host intestine, still results in debilitating acute diarrhea and abdominal pain.

 Sales of refrigerated, processed foods of extended durability including sous-vide foods, chilled ready-to-eat meals, and cook-chill foods have increased over recent years



 As a result of conditions accommodating growth, anaerobic spore-formers have been identified as the primary microbiological concerns in these foods

 . Heightened awareness over intentional food source tampering with botulinum neurotoxin has arisen with respect to genes encoding the toxins that are capable of transfer to nontoxigenic clostridia

 Similarly, enterotoxin produced by C. perfringens and the genomic location of the cpe gene has epidemiologic significance for understanding the capability to cause foodborne disease in humans

 The susceptibility of these bacterial spore-formers to physical and chemical agents is examined as well as recommended control measures

 This information is useful in developing molecular strategies to study virulence genes and their regulation as a means to safer foods.



Bacillus cereus

 The Bacillus cereus group comprises six members: B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis and B. weihenstephanensis

 . These species are closely related and should be placed within one species, except for B. anthracis that possesses specific large virulence plasmids

 . . B. cereus is a normal soil inhabitant and is frequently isolated from a variety of foods, including vegetables, dairy products and meat.



 . It causes an emetic or a diarrhea type of food-associated illness that is becoming increasingly important in the industrialized world

 . Some patients may experience both types of illness simultaneously. The diarrhoeal type of illness is most prevalent in the western hemisphere, whereas the emetic type is most prevalent in Japan.

 Desserts, meat dishes, and dairy products are the foods most frequently associated with diarrhoeal illness, whereas rice and pasta are the most common vehicles of emetic illness



 The emetic toxin (cereulide) has been isolated and characterized; it is a small ring peptide synthesised non-ribosomally by a peptide synthetase.

 Three types of B. cereus enterotoxins involved in foodborne outbreaks have been identified.

 Two of these enterotoxins are three-component proteins and are related, while the last is a one-component protein (CytK).



 )Deaths have been recorded both by strains that produce the emetic toxin and by a strain producing only CytK

 Some strains of the B. cereus group are able to grow at refrigeration temperatures

 . These variants raise concern about the safety of cooked, refrigerated foods with an extended shelf life. B. cereus spores adhere to many surfaces and survive normal washing and disinfection (except for hypochlorite and UVC) procedures



Food- and Waterborne Enteric Viruses

 Food- and waterborne viruses contribute to a substantial number of illnesses throughout the world. Among those most commonly known are hepatitis A virus, rotavirus, astrovirus, enteric adenovirus, hepatitis E virus, and the human caliciviruses consisting of the noroviruses and the Sapporo viruses

 . they are transmitted by the fecal-oral route, often by ingestion of contaminated food and water



Food-and Waterborne Protozoan Parasites

 Protozoan parasites have been associated with food and waterborne outbreaks causing illness in humans. Although parasites are more commonly found in developing countries, developed countries have also experienced several foodborne outbreaks. Contaminants may be inadvertently introduced to the foods by inadequate handling practices, either on the farm or during processing of ready-to-eat foods. In some instances, this contamination occurred in endemic regions and is carried to non-endemic areas where an outbreak is initiated. Other protozoan parasites can be found worldwide, either infecting wild animals or in an environment such as water and eventually finding its way to crops grown for human consumption. Parasites can infect immunocompetent individuals, however the clinical presentation can be much more severe and prolonged in immunocompromissed individuals.



Viable but Non culturable Bacteria in Food Environments

 Cells in the viable but non culturable (VBNC) state are alive, but undetectable by routine microbiological methods.

 The presence of such cells in foods presents a special concern, especially when they are human pathogens.

 Biology of the VBNC state and the factors which induce it, the food borne pathogens that are known to enter this state, how cells resuscitate back to the actively growing state, and the importance of the VBNC state in food microbiology are in need for study



Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

 Traditional microbiological methods for testing foods for the presence of pathogens rely on

 -Growth in culture media, followed by isolation, and biochemical and serological identification.

 Traditional methods are laborious and time consuming, requiring a few days to a week or longer to complete. Rapid detection of pathogens in food is essential for ensuring the safety of food for consumers, and in the past 25 years, advances in biotechnology have resulted in the development of rapid methods that reduce the analysis time.



Two major categories of rapid methods include

 - Immunologic or antibody-based assays

 -Genetic-based assays such as the polymerase chain reaction.

 -Generation assays under development include biosensors and DNA chips that potentially have the capability for near real-time and on-line monitoring for multiple pathogens in foods



-Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.



Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.

You can find more at e-book entiteled lectures on applie clinical microbiology by Maysaa El Sayed Zaki

Food borne Pathogens: Microbiology and Molecular Biology

The following topics will covered by the Lecture


 Pathogens well established as food borne pathogens.

 Viable but Nonculturable Bacteria in Food Environments

 Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

-Microbiological methods for detection of food borne pathogens:

 Traditional methods

 Recent Methods.



The followings are well established as food borne pathogens

 Bacteria

Yersinia enterocolitica

-Vibrio spp.

-Staphylococcus aureus

- Campylobacter Infections.

-Listeria monocytogenes

-Salmonella spp.

-Shigella spp.

-Escherichia coli

-Clostridium botulinum and Clostridium perfringens -Bacillus cereus



Viruses

 hepatitis A virus,

 rotavirus, astrovirus,

 enteric adenovirus,

 hepatitis E virus,

 human caliciviruses consisting of the noroviruses and the --Sapporo viruses



Food-and Waterborne Protozoan Parasites

 Entamoeba species

 Giardia

In addition to Foodborne Mycotoxins: Chemistry, Biology, Ecology, and Toxicology



Yersinia enterocolitica

 Yersinia enterocolitica includes well-established pathogens and environmental strains that are ubiquitous in terrestrial and fresh water ecosystems

 . Evidence from large outbreaks of yersiniosis and from epidemiological studies of sporadic cases has shown that Y. enterocolitica is a food borne pathogen, and that in many cases pork is implicated as the source of infection.



 The pig is the only animal consumed by man that regularly harbours pathogenic Y. enterocolitica

 . An important property of the bacterium is its ability to multiply at temperatures near to 0ƒC, and therefore in many chilled foods

 . The pathogenic serovars (mainly O:3, O:5,27, O:8 and O:9) show different geographical distribution

 The appearance of strains of serovars O:3 and O:9 in Europe, Japan in the 1970s, and in North America by the end of the 1980s, is an example of a global pandemic.

 The possible risk of reactive arthritis following infection with Y. enterocolitica has led to further attention being paid to this microbe



Vibrio spp

 Vibrio species are prevalent in estuarine and marine environments and seven species can cause seafood borne infections

 Vibrio cholerae O1 and O139 serovtypes produce cholera toxin and are agents of cholera. However, fecal-oral route infections in the terrestrial environment are responsible for epidemic cholera.

 V. cholerae non-O1/O139 strains may cause gastroenteritis through production of known toxins or unknown mechanism



 Vibrio parahaemolytitucs strains capable of producing thermostable direct hemolysin (TDH) and/or TDH-related hemolysin are most important cause of gastroenteritis associated with seafood consumption

 Vibrio vulnificus is responsible for seafoodborne primary septicemia and its infectivity depends primarily on the risk factors of the host.



 V. vulnificus infection has the highest case fatality rate (50%) of any food borne pathogen

 Four other species (Vibrio mimicus, Vibrio hollisae, Vibrio fluvialis, and Vibrio furnissii) that have potential to cause gastroenteritis have been reported

 Some strains of these species produce known toxins but the pathogenic mechanism is largely not understood



Staphylococcus aureus

 Staphylococcus aureus is a common cause of confirmed bacterial foodborne disease worldwide

 Food poisoning episodes are characterized by symptoms of vomiting and diarrhea that occur shortly after ingestion of S. aureus-contaminated food.

 The symptoms arise from ingestion of preformed enterotoxin, which accounts for the short incubation time.



 Staphylococcal enterotoxins are a family of sequence similar, but serologically distinct proteins

 . These proteins have the additional property of being superantigens and, as such, have adverse effects on the immune system

 The enterotoxin genes are accessory genetic elements in S. aureus, meaning that not all strains of this organism are enterotoxin-producing.



 The enterotoxin genes are found on prophage, plasmids, and pathogenicity islands in different strains of Expression of the enterotoxin genes is often under the control of global virulence gene regulatory systems S. aureus.

 Although much progress has been made recently in defining enterotoxin structure and superantigenicity properties, much remains to be learned regarding the binding of enterotoxins to receptors in the gastrointestinal tract and how toxin production leads to the symptoms associated with staphylococcal food poisoning.



Campylobacter Infections

 Campylobacter spp., primarily C. jejuni subsp. jejuni is one of the major causes of bacterial gastroenteritis in the U.S. and worldwide.

 Campylobacter infection is primarily a foodborne illness, usually without complications; however, serious sequelae such as Guillain-Barre Syndrome occur in a small subset of infected patients



 Detection of C. jejuni in clinical samples is readily accomplished by culture and non-culture methods, although improvements in diagnostic approaches are needed

 A significant body of knowledge exists on the epidemiology of Campylobacter infections; however, much less is known about the mechanism of disease, despite over 2 decades of research.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Listeria monocytogenes

 Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis

 The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood

 Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters

 Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens .



As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods.



Salmonella spp

The second half of the 20th century saw the emergence of Salmonella serotypes that became associated with new food sources (i.e. chicken eggs) and the emergence of Salmonella serotypes with resistance against multiple antibiotics.



Shigella spp

 Shigella species are members of the family Enterobacteriacae and are Gram negative, non-motile rods

 Four subgroups exist based on O-antigen structure and biochemical properties; S. dysenteriae (subgroup A), S. flexneri (subgroup B), S. boydii (subgroup C) and S. sonnei (subgroup D).

 Clinical manifestations include mild to severe diarrhea with or without blood, fever, tenesmus, and abdominal pain.

 Further complications of the disease may be seizures, toxic megacolon, reactive arthritis and hemolytic uremic syndrome

 . Transmission of the pathogen is by the fecal-oral route, commonly through food and water

 The infectious dose ranges from 10-100 organisms. Shigella spp. have a sophisticated pathogenic mechanism to invade colonic epithelial cells of the host, man and higher primates, and the ability to multiply intracellularly and spread from cell to adjacent cell via actin polymerization



Diarrhea-inducing Escherichia coli

 For many years, E. coli was considered a commensal of human and animal intestinal tracts with low virulence potential.

 Today, it is well known that many strains of E. coli act as pathogens inducing serious gastrointestinal diseases and even death in humans.



 There are six major categories of E. coli strains that cause enteric diseases in humans including the

 (1) enterohemorrhagic E. coli, which cause hemorrhagic colitis and hemolytic uremic syndrome (2) enterotoxigenic E. coli, which induce traveler's diarrhea

 (3) enteropathogenic E. coli, which cause a persistent diarrhea in children living in developing countries

 (4) enteroaggregative E. coli, which provoke diarrhea in children

 (5) enteroinvasive E. coli that are biochemically and genetically related to Shigella species and can induce diarrhea

 (6) diffusely adherent E. coli, which cause diarrhea and are distinguished by a characteristic type of adherence to mammalian cells.



Clostridium botulinum and Clostridium perfringens

 Clostridium botulinum produces extremely potent neurotoxins that result in the severe neuroparalytic disease, botulism

 Although of lower lethality, the enterotoxin produced by C. perfringens, during sporulation of vegetative cells in the host intestine, still results in debilitating acute diarrhea and abdominal pain.

 Sales of refrigerated, processed foods of extended durability including sous-vide foods, chilled ready-to-eat meals, and cook-chill foods have increased over recent years



 As a result of conditions accommodating growth, anaerobic spore-formers have been identified as the primary microbiological concerns in these foods

 . Heightened awareness over intentional food source tampering with botulinum neurotoxin has arisen with respect to genes encoding the toxins that are capable of transfer to nontoxigenic clostridia

 Similarly, enterotoxin produced by C. perfringens and the genomic location of the cpe gene has epidemiologic significance for understanding the capability to cause foodborne disease in humans

 The susceptibility of these bacterial spore-formers to physical and chemical agents is examined as well as recommended control measures

 This information is useful in developing molecular strategies to study virulence genes and their regulation as a means to safer foods.



Bacillus cereus

 The Bacillus cereus group comprises six members: B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis and B. weihenstephanensis

 . These species are closely related and should be placed within one species, except for B. anthracis that possesses specific large virulence plasmids

 . . B. cereus is a normal soil inhabitant and is frequently isolated from a variety of foods, including vegetables, dairy products and meat.



 . It causes an emetic or a diarrhea type of food-associated illness that is becoming increasingly important in the industrialized world

 . Some patients may experience both types of illness simultaneously. The diarrhoeal type of illness is most prevalent in the western hemisphere, whereas the emetic type is most prevalent in Japan.

 Desserts, meat dishes, and dairy products are the foods most frequently associated with diarrhoeal illness, whereas rice and pasta are the most common vehicles of emetic illness



 The emetic toxin (cereulide) has been isolated and characterized; it is a small ring peptide synthesised non-ribosomally by a peptide synthetase.

 Three types of B. cereus enterotoxins involved in foodborne outbreaks have been identified.

 Two of these enterotoxins are three-component proteins and are related, while the last is a one-component protein (CytK).



 )Deaths have been recorded both by strains that produce the emetic toxin and by a strain producing only CytK

 Some strains of the B. cereus group are able to grow at refrigeration temperatures

 . These variants raise concern about the safety of cooked, refrigerated foods with an extended shelf life. B. cereus spores adhere to many surfaces and survive normal washing and disinfection (except for hypochlorite and UVC) procedures



Food- and Waterborne Enteric Viruses

 Food- and waterborne viruses contribute to a substantial number of illnesses throughout the world. Among those most commonly known are hepatitis A virus, rotavirus, astrovirus, enteric adenovirus, hepatitis E virus, and the human caliciviruses consisting of the noroviruses and the Sapporo viruses

 . they are transmitted by the fecal-oral route, often by ingestion of contaminated food and water



Food-and Waterborne Protozoan Parasites

 Protozoan parasites have been associated with food and waterborne outbreaks causing illness in humans. Although parasites are more commonly found in developing countries, developed countries have also experienced several foodborne outbreaks. Contaminants may be inadvertently introduced to the foods by inadequate handling practices, either on the farm or during processing of ready-to-eat foods. In some instances, this contamination occurred in endemic regions and is carried to non-endemic areas where an outbreak is initiated. Other protozoan parasites can be found worldwide, either infecting wild animals or in an environment such as water and eventually finding its way to crops grown for human consumption. Parasites can infect immunocompetent individuals, however the clinical presentation can be much more severe and prolonged in immunocompromissed individuals.



Viable but Non culturable Bacteria in Food Environments

 Cells in the viable but non culturable (VBNC) state are alive, but undetectable by routine microbiological methods.

 The presence of such cells in foods presents a special concern, especially when they are human pathogens.

 Biology of the VBNC state and the factors which induce it, the food borne pathogens that are known to enter this state, how cells resuscitate back to the actively growing state, and the importance of the VBNC state in food microbiology are in need for study



Approaches for Detection, Identification, and Analysis of Foodborne Pathogens

 Traditional microbiological methods for testing foods for the presence of pathogens rely on

 -Growth in culture media, followed by isolation, and biochemical and serological identification.

 Traditional methods are laborious and time consuming, requiring a few days to a week or longer to complete. Rapid detection of pathogens in food is essential for ensuring the safety of food for consumers, and in the past 25 years, advances in biotechnology have resulted in the development of rapid methods that reduce the analysis time.



Two major categories of rapid methods include

 - Immunologic or antibody-based assays

 -Genetic-based assays such as the polymerase chain reaction.

 -Generation assays under development include biosensors and DNA chips that potentially have the capability for near real-time and on-line monitoring for multiple pathogens in foods



-Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.



Biosensor-based Detection of Food borne Pathogens

The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs



Molecular Typing and Differentiation of Food borne Bacterial Pathogens

 Molecular typing of food borne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time.

 Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls.