Final answer:
The correct option is C). The diameter of the zone of inhibition surrounding the antibiotic disks in the Kirby-Bauer test is used to determine microbial susceptibility to antibiotics. Scientists measure this zone and compare it to a standardized chart to determine resistance or susceptibility.
Step-by-step explanation:
Kirby-Bauer Disk Diffusion Test
The characteristic of the Kirby-Bauer test that helps scientists determine if a microorganism is susceptible to an antibiotic is C. The diameter of the zone of inhibition surrounding the antibiotic disks. In the test, filter paper disks impregnated with antibiotics are placed on an agar plate inoculated with the microbe. If the microbe is susceptible to the antibiotic, a clear zone known as the zone of inhibition appears around the disk. This occurs because the antibiotic diffuses into the agar and inhibits microbial growth in that area. The size of the zone of inhibition, measured in millimeters, is compared to a standardized chart to determine whether the microbe is susceptible or resistant to the antibiotic. The disk-diffusion method is a straightforward and rapid means of assessing the effectiveness and evaluating the susceptibility and resistance of a bacterial pathogen to various antibiotics.