Minimum inhibitory concentrations (MICs) are properties of drugs, not of a microbe. The minimum inhibitory concentration (MIC) of an antibiotic is the minimum concentration to inhibit the growth of a microorganism.

Where the MIC value for a bacterial isolate is below the ECOFF, the bacterium is likely to be from a wild-type drug-susceptible population; where the MIC value is above the ECOFF the bacterium is likely to be resistant.

ECOFF values are based on microbiological studies, and do not necessarily indicate whether a drug will be clinically active, since they do not take into account what happens to an antibiotic within the body (pharmacokinetics). ECOFF values are not the same as clinical breakpoint concentrations.