Which method is used to determine the minimum inhibitory concentration (MIC) of an antibiotic?

The method used to determine the minimum inhibitory concentration (MIC) of an antibiotic is widely recognized as the broth microdilution method. This technique allows for the precise quantification of the lowest concentration of an antibiotic that will inhibit the visible growth of a microorganism. In this method, a series of test tubes or wells are prepared with varying concentrations of the antibiotic, and a standardized number of bacteria is added to each tube. After incubation, the tubes are examined for bacterial growth, and the lowest concentration at which no growth is observed is recorded as the MIC.

While antibiotic susceptibility testing is a broader category that encompasses various methods for evaluating how effective an antibiotic is against specific bacteria, it is not a specific assay for determining MIC. The disk diffusion method is primarily used to gauge susceptibility by observing the zone of inhibition around an antibiotic disk on an agar plate, rather than quantifying the minimum concentration that inhibits growth. Blood agar plating is a culture medium that supports the growth of bacteria but does not provide quantitative information about antibiotic effectiveness.

Therefore, the broth microdilution method is the most appropriate choice for accurately determining the MIC of an antibiotic, as it provides direct measures and is essential in clinical microbiology for guiding effective treatment.