Question

What is the difference between a Kirby-Bauer susceptibility test, E-test diffusion test, and tube dilution test? What do they have in common?

Answer 1

All these tests are performed to screen antimicrobial susceptibility test. In all these test a concentration gradient is established inorder to identify the antimicrobial activity. All these test leads to determine the minimum inhibitory concentration.

In Kirby Bauer method a sutable nutrient medium eg. Muller Hinton agar medium. Is swabbed using respective test organism and after which a filter paper disc dipped in antimicrobial agent which is dried is placed over the agar media . Two or more antimicrobial agents can be studied in a single plate. The plate is incubated and are observed for zone against the control disc and minimum inhibitory concentration(MIC) is determined.

In E-test plastic strips are used to determine MIC. The plate is swabbed using test organism . The strip which contain antimicrobial agent on a side and numerical value of gradient on other side is placed over the media. After incubation the zone is determined depending on numerical value.

In tube dilution method antimicrobial agent is diluted and kept in a series of increasing fold in each tube . The test organism is inoculated and incubated . After incubation the MIC is determined by observing the turbdity. The concentration which will completely or mostly is choosen as MIC.