High School

What is the primary purpose of the Kirby-Bauer disk diffusion test?

A) To determine the minimal inhibitory concentration (MIC) of an antibiotic
B) To identify bacterial species based on their antibiotic resistance
C) To test the effectiveness of different antibiotics on a bacterial strain
D) To determine bacterial growth rate in the presence of antibiotics

Answer :

The primary purpose of the Kirby-Bauer disk diffusion test is to test the effectiveness of different antibiotics on a bacterial strain. Therefore, the correct answer is C) To test the effectiveness of different antibiotics on a bacterial strain.

The Kirby-Bauer disk diffusion test, also known as the agar diffusion test, is a method used to evaluate whether certain antibiotics can effectively inhibit the growth of specific bacteria. Here’s how the test generally works:

  1. Preparation of Culture Medium: A Petri dish is filled with agar (a gel-like substance derived from seaweed) which acts as a growth medium for bacteria.

  2. Inoculation of Bacteria: A sample of bacteria is evenly spread across the agar surface to ensure consistent growth during testing.

  3. Application of Antibiotic Disks: Small paper disks impregnated with known concentrations of different antibiotics are placed on the surface of the agar.

  4. Incubation: The Petri dish is then incubated at a specific temperature to allow the bacteria to grow. During this period, antibiotics diffuse from the disks into the agar.

  5. Observation of Results: After incubation, the Petri dish is examined for zones of inhibition - clear areas around the disks where bacteria have not grown. The size of these zones indicates the effectiveness of the antibiotic; larger zones suggest more effective inhibition of bacterial growth.

This test is crucial in clinical settings to help determine which antibiotics a particular bacterial infection is susceptible to, thus guiding proper treatment choices. Understanding which antibiotics are effective helps in combating antibiotic resistance by avoiding the use of ineffective treatments.