Wednesday, August 24, 2011

Laboratory diagnosis of Infectious syndromes

1-1-Sample collection
Before antibiotics
Avoid sites of resident flora
Use appropriate Cole action systems
2-Laboratory methods cultural techniques and antibiotics sensitivity
3-Transport to laboratory
Inform Lab about required laboratory procedures
Microbiological Methods
1-Non cultural techniques
1- macroscopic examination
2- microscopic examination:
*Wet smear:
Physiological saline.
Potassium hydroxide
Indian preparations
*Stained smears.
Gram stain
Zeihl – Nelson stain
*Fluorescent stain
Non labeling
Labeled antibodies
Special technique use for staining
3. Direct antigen detection methods:-
-Latex agglutination
-Haemagglutination inhibition
-RIA (Radio immunoassay)
-coagyhutination method
-Immunofluorescent and Immune cytochemical
4- Serodiagnostic tests:
Techniques include ELISA, agglutination , complement fixation, neutralization
-Diagnosis of acute infection:-
Paired sera to determine the rise in specific IgG titre at least four folds within period approximately 7-10 days according to type of infection.
-Single acute IgM raised titre.
5-Nucleic acid techniques:-
- Plasmid fingerprinting
- Restriction enzyme
- Nudcleic acid probe assays.
- Sequencer and microchip technology to detect viral genomes quiascpiescies in hepatitis Chris infection, drugresistance
2-Culture techniques:-
- on selective or enriched media
- Idenitify the colonies by biochemical testing either manual, semiautomated or fully automated
- Identification of the organisms if contaminant, infectious agents, colonization
Primary identification
Gram positive cocci Gram negative
Hemolysis B hemolysis Gamma hemolysi
Catalase tests
Coagulate tests
Gram positive bacilli. Listerine monocytogenes
3-Antimicrobial susceptibility testing
1-Disc diffusion tests
Limitation of disc diffusion tests:-
-Not applied to slowly –growing, Fastidiwaws organisms or onaeroben .
-My cobacterial and jungle susceptibility testing revires specific techsiques
- 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 fliud levels of
-Bacteriostatic measures only.
-Can’t be applied to certain antibiotics such as polymyxines.
2,Dilution susceptibility testes:-
(micro) minimal inhibitory can cedtration and minimal bacrticidal activity. methods.
-Broth dilution tests
-Agar dlution method.
-Serious infection where endpoint concentration is ended
-Disc diffusion yield inter mediate susceptibility
-Life threatening infection due to organisms with un predictable susceptibitlitu pattern.
-Fastidious or slowly growing organisms.
-Failure of antibiotic therapy
-Serious infections caused by organisms susceptible only to toxic agents
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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