Antimicrobial Susceptibility Testing Flashcards
What are antimicrobial tests?
In vitro testing of a particular antimicrobial agent against individual strains of bacteria
Four important aspects of AST
Sensitivity testing must:
- Give reproducible results (across all labs)
- Be easy to interpret
- Be rapid (high throughput)
- Be useful for epidemiological studies
State the four reasons why we test for antimicrobial susceptibility
- To direct and predict antimicrobial chemotherapy (effectiveness)
- To review and monitor epidemiological trends (emergency and spread of resistant strains in humans and animal populations)
- To set national and local antibiotic policies
- To test the activity of a new antimicrobial agent
Minimum Inhibitory Concentration (MIC)
Lowest concentration of an antimicrobial agent that visibly inhibits the growth of the organism (bacteriostatic)
Susceptibility Breakpoint
What happens if the MIC is less than or equal to the susceptibility breakpoint?
Agreed concentration (mg/L) of an antibiotic which defines whether a species of bacteria is susceptible or resistant to the antibiotic
The bacteria is considered susceptible to the antibiotic
Susceptible (S)
An organism that is inhibited by the recommended dose, at the infection site, of an antimicrobial agent
Intermediate (I)
An organism that may require a higher dose of antibiotic for a longer period of time to be inhibited
Resistant (R)
An organism that is not inhibited by the recommended dose, at the infection site, of an antimicrobial agent
List six common testing methods
- Broth dilution
- Agar incorporation (similar to broth dilution)
- Disk diffusion/Kirby-Bauer
- E test
- Automated systems
- Molecular methods
Minimum Bactericidal Concentration (MBC)
Antibiotic concentration that kills the bacteria (usually higher than MIC concentration)
