Question

Colonies in the zone represent resistant bacteria. Interpreting the Results of the Bauer Kirby Method of Antibiotic Susceptibility Testing

Answer 1

The Bauer Kirby method or Disk diffusion method is the preliminary method to test antibiotic sensitive. It is a sensitive,cheap,simple and quick method to assess the sensitivity of a bacteria towards a particular antibiotic.

This method involves the even spreading of the bacteria on a media plate followed by embedding commercially available concentrations of the desired antibiotic or dipping plane discs into a specific concentration of an antibiotic and placing them on the plate.

The bacteria grows evenly on the plate. If the bacteria is sensitive to the antibiotic then there will be a clear zone of no growth around that disc.

In this given picture, only 1 disc shows a clear zone around it which means only this particular antibiotic at that specific concentration is effective in inhibiting the growth of that microbe. to further clarify, the zone of inhibition can be measured(diameter of inhibition) and tabulated. The more the diameter means more the inhibition and vice versa.

The MIC(Minimum inhibitory concentration) is usually found at the end of this experiment. It is the minimum concentration of an antibiotic that is required to inhibit the growth of the microbes. It is also called disc diffusion method because the antibiotic diffuses out into the agar media and eventually inhibits growth of microbes around that region.

Big zones of inhibition means the organism is very sensitive, and no inhibition means that it is resistant. According to this the ideal dosage to be given can be identified. Since unnecessary prescriptions can lead to antibiotic resistance which is currently a global threat. BActeria are evolving to become multi drug resistant posing great threats. Hence in these studies the kirby-bauer method is the 1st step in identifying the nature of bacteria-antibiotic interactions.