Name one method used in microbiology to determine the susceptibility of bacteria to antibiotics.

The Kirby-Bauer disk diffusion test is a widely used method in microbiology for determining the susceptibility of bacteria to antibiotics. In this procedure, bacterial isolates are cultured on an agar plate, and paper disks infused with specific antibiotics are placed on the agar surface. After incubation, the bacteria will grow except where the antibiotic has inhibited growth, creating a clear zone around the disks. The diameter of these zones can then be measured and interpreted to assess whether the bacteria are susceptible, intermediate, or resistant to the antibiotics tested.

This method is practical because it provides a visual representation of antibiotic effectiveness and is relatively easy to perform, making it a standard laboratory technique. In contrast, the other methods listed pertain to different aspects of microbiological research, such as detection of specific DNA sequences (PCR), quantifying antigen-antibody interactions (ELISA), or analyzing protein expression (Western blotting), but none are used specifically for assessing antibiotic susceptibility in the way that the Kirby-Bauer test is.