Tuesday, May 31, 2011

Antimicrobial susceptibility testing

Antimicrobial susceptibility testing

Definition: In vitro study of bacterial susceptibility to antibiotics.


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.


-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 unpredictable susceptibility 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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