The minimum inhibitory concentration (MIC) is the lowest concentration of an antimicrobial that visibly inhibits the growth of a microorganism in vitro.
Explanation
MIC testing provides a quantitative measure of microbial susceptibility. It is determined by exposing a standardized inoculum to serial dilutions of the antimicrobial agent and observing the lowest concentration that prevents visible turbidity after incubation. The MIC is specific to the organism–drug combination and reflects the ability of the drug to inhibit growth rather than kill cells. In clinical laboratories, broth microdilution, agar dilution and automated systems are used to generate MIC values, which guide selection of effective antimicrobials and dosing regimens. Interpretation relies on clinical breakpoints defined by organizations such as the Clinical and Laboratory Standards Institute and the European Committee on Antimicrobial Susceptibility Testing. Factors including inoculum size, incubation conditions and medium composition can influence MIC results, so standardization is essential. While MIC does not measure bactericidal activity, comparison with the minimum bactericidal concentration (MBC) can distinguish between bacteriostatic and bactericidal agents. MIC data also contribute to surveillance of antimicrobial resistance and development of new drugs.
Applications and Considerations
- MIC values guide clinicians in selecting antibiotics and dosing regimens, ensuring concentrations achieved in serum or tissues exceed the MIC of the pathogen.
- Broth microdilution and automated susceptibility testing platforms routinely report MICs in clinical microbiology laboratories.
- Pharmacokinetic/pharmacodynamic modelling uses MIC in conjunction with drug exposure profiles to optimize therapy.
- Variability in MIC determination due to inoculum density, incubation time and medium underscores the need for standardized methods.
Determining the MIC is a fundamental step in evaluating antimicrobial activity and informing patient care. Although it reflects inhibition rather than killing, MIC testing remains a cornerstone of antimicrobial susceptibility testing and resistance surveillance.
Related Terms: MBC, Disk Diffusion, Breakpoint, Susceptibility, Dilution Test