Question

In performing a kirby bauer test, you determine that one organism is resistant to nonvobiocin while other is not. How would you explain the organism's different antibiotic susceptibilities?

Answer 1

Kirby bauer test also known as disc diffusion method is an important susceptibility test used to ascertain the susceptibility or resistance of different strains of various pathogenic ,aerobic and facultative anaerobic bacteria towards different antibiotics.

For performing this test,the pathogens are grown on Mueller Hinton Agar.6 mm filter paper discs are used soaked in different antibiotics to be tested.

The bacteria or the pathogen is swabbed on the solid agar media and the antibiotic discs are placed on top of it.The antibiotic from the filter paper gets soaked into the media.As the distance from the disc increases the amount of the antibiotic present in the surrounding medium decreases.If the bacteria is susceptible to the antibiotic their will be no growth in the surrounding areas of the filter disc which is known as Zone of Inhibition.If the bacteria is resistant to the antibiotic we can see the bacterial colonies around the filter disc soaked in antibiotic.The zone of Inhibition is measured and compared to the set criteria of Clinical and Laboratory Standards Institute(CLSI),based on which the bacteria can be labelled as resistant intermediate or susceptible.

Following this method an organism's sensitivity towards different antibiotic can be determined.