What is the difference between an MIC (Minimum Inhibitory Concentration), an MBC (Minimum Bactericidal Concentration) and a breakpoint?
The minimum inhibitory concentration (MIC) is the concentration required to inhibit growth of a specific isolate in vitro under standardized conditions. It is determined by finding the lowest dilution without visible growth during serial dilution testing. This will vary for individual isolates. The minimum bactericidal concentration (MBC) is the lowest dilution where the culture has been completely sterilized. It is not routinely determined. Treatment decisions are made related to MICs, and more specifically, the breakpoint MICs. A breakpoint is an MIC selected to predict clinical outcome for a specific pathogen, in a specific disease, in a specific species, given a specific regimen (dose, route, duration, frequency). A breakpoint MIC is typically selected for susceptible, intermediate susceptibility, and resistant. Some drug/pathogen combinations only have a susceptible and resistant breakpoint. Serial dilution testing example: The figure below illustrates serial 1:2 dilutions of an a