Lecture 21: Antimicrobial Susceptibility Testing Flashcards
Two tests that use dilution methods
- Broth dilution test (quant)
- Agar dilution test (quant)
Agar diffusion methods
- Disk/tablet test (semi-quant)
- Gradient diffusion E-test (quant)
Diffusion methods enable quantification of antimicrobial susceptibility by determining:
- Minimum inhibitory concentration
- Minimum bactericidal concentration
MIC
The lowest concentration that inhibits complete growth of the test strain
MBC
Lowest concentration that kills the test strain
Is serial dilution susceptibility testing MIC/MBC accurate?
Nope, because it reflects a range
Two types of broth dilution
Macro and micro dilution
Microdilution enables
automated or semiautomated reading
Agar dilution is primarily used for
Research purposes
Ex. When many strains have to be tested with one drug
Breakpoint
A drug-specific value to interpret the results of susceptibility testing and determine if an antibacterial is potentially useful in the treatment of a bacterial infection
A strain is defined as susceptible by
A level of antimicrobial activity associated with a high likelihood of therapeutic success
A strain is defined as resistant by
A level of antimicrobial activity associated with a high likelihood of therapeutic failure
Mixed cultures are frequent with
otitis externa, wound infections, and UTI’s
Surrogate antimicrobials are used when?
In the lack of approved clinical breakpoints to predict susceptibility to other drugs belonging to the same class
Two drugs used to ID MRSA/MRSP
- Oxacillin
- Cefotoxin
