Question

Kirby-Bauer Method Question

a.) Would you expect Penicillin G to show a Zone of Inhibition around its disk on a plate inoculated with E. coli? Explain briefly?

b.) Would you expect a different generation of beta-lactam inhibitors like Amoxicillin with Clavulanic Acid - would it have an effect in controlling E. coli? Explain briefly?

Answer 1

a) The zone of inhibition is a circular area of no bacterial growth signifying that the colony is sensitive to the particular antibiotic. Penicillin G or benzylpenicillin is a narrow spectrum antibiotic effective against gram positive bacterium and is usually not effective against E.coli. Hence, a zone of inhibition might not be observed.

b) the combination might be effective against E.coli. In one study it was reported that susceptibility to amoxicillin clauvanate was present in E.coli. Furthermore, amoxicillin is a broad spectrum semi synthetic antibiotic and is effective against both gram positive and gram negative bacterium.