What is the Kirby-Baur Method?

Answer 1

The Kirby-Bauer methods is a standardized system that takes all variables into consideration:

The recommended medium in this test is Mueller-Hinton II agar. Its pH should be between 7.2 and 7.4, and it should be poured to a uniform thickness of 4mm in the petri plate. This requires 60 ml in a 150 mm plate and 25 ml in a 100 mm plate. For certain fastidious organisms, 5% defibrinated sheep blood is added to the medium.

Inoculation of the surface of the medium is made with a cotton swab from a broth culture. High-potency disks are used that may be placed on the agar with a mechanical dispenser or sterile forceps. To secure the disks to the medium, it is necessary to press them down ont the agar.

After 16 to 18 hours incubation, the plates are examined and the diameters of the zones are measured to the nearest millimeter. In this case, we are measuring what is called the "zone of inhibition" or where no growth occurs. And lastly, record your results. The zone diameter is compared to a standard table for that drug and concentration, and the organism is reported as sensitive, intermediate, or resistant. For a drug with poor solubility, however, the zone of inhibition indicating that the microbe is sensitive will usually be smaller than for another drug that is more soluble and has diffused more widely. Results obtained by the disk-diffusion method (AKA Kirby-Bauer test) are often inadequate for many clinical purposes. However, the test is simple and inexpensive and is most often used when more sophisticated laboratory facilities are not available.