Final answer:
The Kirby-Bauer disk diffusion test measures the diameter of the zone of inhibition to interpret bacterial susceptibility to antibiotics, with larger zones generally indicating more effective inhibition.
Step-by-step explanation:
In the Kirby-Bauer disk diffusion test, the correct answer to the student's question is that the diameter of the zone of inhibition is measured and used for interpretation. This method evaluates the susceptibility of bacteria to antibiotics by placing drug-impregnated disks on an agar plate inoculated with a bacterial lawn. After incubation, areas where bacterial growth has been inhibited, known as zones of inhibition, appear as clear rings around the disks. The diameter of these zones, measured in millimeters, is then compared to a standardized chart to determine whether the bacteria are resistant, susceptible, or have intermediate susceptibility to the antibiotics tested.
The zone's diameter provides important data regarding the bacteria's response to the antimicrobials, though it does not inform on the bacteriostatic versus bactericidal nature of the antibiotics or allow comparison of drug potencies. The assumption is that a larger zone typically suggests more effective inhibition by the antimicrobial agent, assuming other factors such as solubility and diffusion rate through the agar are constant.