How long should Mueller-Hinton plates dry after inoculation before adding antibiotic disks in the Kirby-Bauer test?

In the Kirby-Bauer test, the proper drying time for Mueller-Hinton plates after inoculation is crucial to ensure accurate susceptibility testing. The plates should be allowed to dry for at least 3 minutes but not more than 15 minutes before antibiotic disks are applied.

This drying time allows the excess moisture from the inoculated broth to evaporate, ensuring that the antibiotic disks can be evenly distributed and will diffuse properly into the agar medium once placed. If the plates are too moist, the antibiotic may not diffuse adequately, potentially leading to unreliable results. Conversely, if the plates are dried for too long, it may lead to uneven diffusion as well.

Therefore, the recommended drying interval is designed to strike a balance between having a surface that is not too wet while also preventing excessive drying, which can compromise the test results. This careful control over the environment helps to ensure the accuracy of the antimicrobial susceptibility profile being determined.