Microbiology homework?

Question

You have found the zone of inhibition of 14mm for E.coli with antibiotics A and B but your collegues argues that the zone of inhibition of 14mm with antibiotic B though it is comparable to the size of zone of inhibition by antibiotic A, still the organism is not sensitive to antibiotic B. Provide arguments in favor or against , to justify the report.

Answer 1

do your own home work!

Answer 2

You're describing the Kirby-Bauer method of susceptibility testing using a confluent growth of bacteria on a Mueller-Hinton agar.  At the time of inoculation of the bacteria onto the media, discs impregnated with different types of antibiotics are dropped onto the surface of the agar.  The agar is incubated overnight and then examined for growth and inhibition of growth around the discs.  Each antibiotic disc has its own assigned zone of inhibition which is based upon the type of antibiotic, the concentration of the antibiotic in the disc, and the organism being tested.  These zones are established based upon the correlation of the antibiotic's activity in vivo as compared to it's effectiveness against an organism in vitro.  So, comparing zones of inhibition of different antibiotics is like comparing apples and oranges.