Minimum inhibitory concentration

Minimum inhibitory concentration (MIC), in microbiology, is the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation. Minimum inhibitory concentrations are important in diagnostic laboratories to confirm resistance of microorganisms to an antimicrobial agent and also to monitor the activity of new antimicrobial agents.

MICs can be determined by broth dilution methods usually following the guidelines of a reference body such as the CLSI, BSAC or EUCAST. Another, more modern method is the E-test method using strips of a gradient of antibiotic concentration.

E-test strips create ellipses of microbial inhibition [1]. The point at which the MIC is taken within the ellipse of inhibition is the point where the bacterial growth crosses the strip [2]

Clinically, the minimum inhibitory concentrations are used not only to determine the amount of antibiotic that the patient will receive but also the type of antibiotic used, which in turn lowers the opportunity for microbial resistance to specific antimicrobial agents.