Question

1. How can you prove that antibiotic used in Kirby-Bauer (disk diffusion) test is bactericidal? How would you explain the presence of isolated colonies within an otherwise clear zone of inhibition produced in Kirby-Bauer (disk diffusion) test?

Answer 1

The antibiotic used in Kirby - Bauer test is bactericidal can be proved by:

• By testing patients pathogen suspectibility or resistance to the disease by undergoing various treatments with various concentrations of antibiotic.  
• by using Zone of inhibition. in bacteicidal pathogens, pathogens can't grow in this zone as antibiotic interfers with components that bacteria need to survive.
• If standard zone is less than or equal to zone of inhibition, then the pathogen is sensitive to antibiotics..

Presence of isolated colonies within zone of inhibition in  disk diffusion :

• In zone of inhibition, normally pathogens can't grow because antibiotic interfers with components that bacteria need for survival.
• presence of isolated colonies indicate that the pathogen is resistant to overcome the antibiotic effect , thus bacteria can survive.