minimum inhibitory concentration
The minimum inhibitory concentration, or MIC, is the lowest concentration of an antibiotic that stops bacteria from visibly growing in a test tube or plate. It is the single most useful number for asking, in the lab, how potent a drug is against a particular bug.
To measure it, a fixed number of bacteria are exposed to a series of two-fold dilutions of the drug and incubated overnight. The lowest concentration where no turbid growth appears is the MIC, usually reported in micrograms per milliliter. A lower MIC means a more potent drug against that strain; a rising MIC over time is an early fingerprint of resistance emerging.
MIC is what clinical labs compare against breakpoints to call an organism susceptible or resistant, and what medicinal chemists track while optimizing an antibacterial series. The honest caveat is that MIC is an in-vitro snapshot: it ignores whether the drug actually reaches the infection site, how protein binding lowers free drug, and the difference between merely stopping growth and truly killing — which is captured by the related minimum bactericidal concentration.
If an isolate of E. coli shows an MIC of 0.5 µg/mL for ciprofloxacin and the susceptibility breakpoint is 0.25 µg/mL, the lab reports it as resistant.
Comparing MIC to a breakpoint turns a number into a clinical call.
MIC measures inhibition, not killing. A bacteriostatic drug can have a low MIC yet leave living bacteria behind that the immune system must finish off.