Final answer:
The Kirby-Bauer disk diffusion test measures bacterial susceptibility to antibiotics by observing zones of inhibition around filter paper disks impregnated with antibacterial drugs on an agar plate inoculated with bacteria. Factors influencing the size of these zones include drug solubility and diffusion rate. Despite limitations, this test is a rapid screening tool used since the 1950s.
Step-by-step explanation:
Kirby-Bauer Disk Diffusion Assay for Antimicrobial Susceptibility
The Kirby-Bauer disk diffusion test is a standardized method used to determine the antimicrobial susceptibility of bacteria. This test employs filter paper disks, which are saturated with specific antibacterial drugs and then placed onto a Mueller-Hinton agar plate that has been inoculated with a bacterial lawn. As the bacteria replicate, the antibiotic diffuses into the agar and impedes bacterial growth, creating zones of inhibition - clear areas surrounding the disks. The diameter of these zones, measured in millimeters, provides a measure of susceptibility or resistance to the drugs.
Factors like drug solubility, rate of diffusion through the agar, the thickness of the medium, and the concentration of the drug on the disk can all impact the size of these zones. However, the zones of inhibition are primarily indicative of whether the bacteria are susceptible or resistant to the antibacterial agents.
The Kirby-Bauer test has been useful since the 1950s due to its simplicity and speed, providing initial information on which antibiotics might be effective for treating an infection. Despite its limitation in distinguishing between bacteriostatic and bactericidal activities, the assay serves as a crucial preliminary screening tool in clinical settings.