Agar Dilution MIC Test

The agar dilution MIC test is a quantitative method for the determination of in vitro activity of an antimicrobial agent against bacterial isolates. A series of agar plates, each containing a unique concentration of an antimicrobial agent, is inoculated with up to 36 isolates per plate. Following incubation using conditions appropriate for the test organisms, the MIC is determined by observing the lowest concentration of antimicrobial agent that inhibits visible growth of each test isolate. MICs obtained are interpreted as susceptible, intermediate, resistant, or nonsusceptible based on criteria defined by the CLSI (1, 2).