Question

You perform a Kirby-Bauer disk diffusion test to determine antibiotic susceptibilities of a clinical isolate. There is a clear zone of several millimeters around the penicillin disk, but there are two to three distinct colonies in the middle of the clear halo. What is the probable explanation for those colonies?

Answer 1

ANSWER :-

Kirby-Bauer disc diffusion test is first of all used to determine whether a particular microbial species is susceptible to a particular antibiotic. Thus, this test helps to identify the sensitivity of a particular microbe towards a particular chemical such as penicillin.

The small clear zone which is formed surrounding the disc containing the antibiotic, which indicates that the microbes are not able to grow and this forms the zone of inhibition.

If some bacterial colonies are seen in this zone of inhibition, this indicates that the isolates are resistant to the antibiotic or in other words, they are antibiotic resistant.