Antimicrobial Susceptibility test

testing sensitivity of the pathogen to specific antibiotics in order to choose best antimicrobial therapy.

judged by determination of MIC and MBC.

Minimum Inhibitory Concentration (MIC):laboratory term that defines the lowest concentration (μg/mL) of the antibiotic that is able to inhibit growth of the microorganism.

Minimum Bacteriosidal Concentration (MBC):laboratory term that defines the lowest concentration (μg/mL) of the antibiotic that is able to kill 99% of the organism.

Antimicrobial Susceptibility testCommon methods

1. Disk diffusion test:The antibiotic diffuses from an impregnated paper disc into an agar medium on which the test organism is growing.

Disk diffusion testKirby – Bauer test

Zone of growth inhibition

Antimicrobial susceptibility test2. E-test

The antibiotic diffuses from an impregnated strip containing gradient concentration an agar medium on which the test organism is growing.

Antimicrobial susceptibility test

3. Agar incorporation assaysThe antibiotic dilutions are incorporated in an agar medium and spot inoculated with a number of test organisms.

Incubation

Antimicrobial susceptibility test

4. Broth dilution assaysSerial dilutions of the antibiotic in growth medium are inoculated with the test organism.

5. Automated Systems: VITEK.

Antibiotic concentration mg/ml64 32 16 8 4 0