Minimum inhibitory concentration

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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.^[1] An MIC is generally regarded as the most basic laboratory measurement of the activity of an antimicrobial agent against an organism.^[2]

MICs can be determined by agar or broth dilution methods usually following the guidelines of a reference body such as the CLSI, BSAC or EUCAST. There are several commercial methods available, including the well established Etest strips and the recently launched Oxoid MICEvaluator method.

The Etest system comprises a predefined and continuous concentration gradient of different antimicrobial agents, which when applied to inoculated agar plates and incubated, create ellipses of microbial inhibition [1]. The MIC is determined where the ellipse of inhibition intersects the strip, and is easily read off the MIC reading scale on 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.

[edit] References

1. ^ Andrews, J. M. Determination of minimum inhibitory concentrations. Journal of Antimicrobial Chemotherapy 48 (Suppl. 1):5-16, (2001). PMID 11420333.
2. ^ Turnidge JD, Ferraro MJ, Jorgensen JH (2003) Susceptibility Test Methods: General Considerations. In PR Murray, EJ Baron, JH Jorgensen, MA Pfaller, RH Yolken. Manual of Clinical Microbiology. 8th Ed. Washington. American Society of Clinical Microbiology. p 1103 ISBN 1-55581-255-4