Sunday, June 12, 2011

Escherichia coli associated Gastrointestinal Infections.

E.coli causes panoply of human infections ranging from gastrointestinal disturbances to extraintestinal illnesses. These diseases include both well-recognized diarrheal syndromes and less frequently encountered enteritis such as wound infections. These organotropic diseases are not the results of random infection but rather are caused by strains possessing specific somatic (O-antigen). E.coli is consider a major cause of gastroenteritis maglobal basis particularly in persons with recent histories of foreign traveler. However, diarrheagenic strains of E.coli are difficult to diagnose in clinical laboratory.

Transmission of intestinal disease is commonly by the fecal/oral route, with contaminated food and water serving as vehicles for transmission

Today the number of types of E.coli associated with gastroenteritis has greatly expanded to include both well recognized categories (eg., Enteropathogenic E.coli ) and newly described groups implicated as possible causes of gastroenteritis (eg., cytotoxic nercotizing factor {CNF}). producing E.coli.

E.coli may cause several types of diarrheal illness. There are five major categories of diarrhegenic E.coli, based on definite virulence factors, clinical manifestations produced, epidemiology, and different O:H stereotypes.

These include the following:

• Enteropathogenic Escherichia coli (EPEC), which cause infantile entritis, especially in tropical countries.

• Enteropathogenic Escherichia coli (EPEC), which are responsible for community acquired diarrheal disease in areas of poor sanitation and are the commonest cause of traveller’s diarrhea.

• Entero-invasive Escherichia coli (EIEC), which cause an illness resembling Shigella dysentery in patients of all ages.

• Enterohemorrhagic Escherichia coli (EHEC), which caused disease in developed countries. Stereotype O157:H7.

• Entero-aggregative Escherichia. coli (EaggEC), which cause chronic diarrhaeal disease in certain developing countries.

Enterotoxigenic E.coli (ETEC).

ETEC is defined as the E.coli strains that elaborate at least one member of two defined groups of enterotoxins: a heat liable toxin (HLT) and aheat stable toxins(HST). The first is a heat-labile enterotoxin (LT) that shows approximately 80% protein sequence identify with the heat-labile cytotoxinic cholera toxin of vibrio cholerae. The second toxin produced by ETEC is a heat-stable with a molecular mass of about 2Kda. Previous studies suggested that ETEC strains carrying both toxins (HLT+ and HST+) predominate clinically followed in decreasing frequency by strains carrying HSt+ only and those carrying HLT+ only. However, a 1996 review of 700ETEC strains collected over a period of more than 30 years found that the relative prevalence of these toxins type I is not different and that individual toxin-producing patterns may be related to serogroup specificity.


ETEC strains are associated with two major clinical syndromes: weaning diarrhea among children in the developing world, and traveler’s diarrhea. The epidemiologic pattern of ETEC disease is determined in large part by a number of factors: (I) Mucosal immunity to ETEC infection develops in exposed individuals, (ii) Even immune asymptomatic individuals may shed large numbers of virulent ETEC organisms in the stool, and (iii) The infection requires a relatively high infectious dose These three features create a situation in which ETEC contamination of the environment in areas of endemic infections is extremely prevalent, and most infants in such areas will encounter in warm-climate countries are not well under stool, but it seems likely that water contaminated by human (or) animal sewage plays an important part in the spread of infection.

Clinical symptoms.

The most common symptoms associated with ETEC infection are diarrhea (91-97%) and abdominal cramps (80-94%). Stools are typically watery in consistency, often yellow-tinged, and without the presence of mucus, pus or fecal leukocytes.

The gastroentritis induced by ETEC infection is typically indicating guishable from secretory diarrheas elicited by other gram-negative enteropathogens. Less often nausea (39-70%), headaches (35-57%), myalgia (50%), weakness (35%). Chills (31%), and low grade fevers (13-22%) are observed.

Vomiting (2-1%) is not commonly associated with ETEC infection, a fact that helps distinguish this illness from gastrointestinal disturbances caused by norwalk virus.

ETEC infections commonly occur in four settings. In less developed countries, ETEC infection predominates in children younger than years of age. Unlike the relatively mild infections, ETEC gastroentritis in young children in underdeveloped nations can be serve at times, with dehydration and adverse nutritional consequences leading to retardation of normal growth development.

Dehydration has also been noted as a consequence of ETEC infection in industrialized countries. As children mature, the incidence of ETEC disease apparently declines, suggesting that immunity may develop in local inhabitants with advancing age.

You need to know about laboratory diagnosis of gastroenteritis?
read at Lectures on applied clinical microbiology

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