Minimum inhibitory concentration
In microbiology, the minimum inhibitory concentration (MIC) is the lowest concentration of a chemical which prevents visible growth of a bacterium. This is in difference to the minimum bactericidal concentration (MBC), which is the concentration resulting in microbial death as defined by the inability to re-culture bacteria. The closer the MIC is to the MBC, the more bactericidal the compound.
The MIC of a chemical is determined by preparing solutions of the chemical in vitro at increasing concentrations, incubating the solutions with the separate batches of cultured bacteria, and measuring the results using agar dilution or broth microdilution. Results have been graded into susceptible (often called sensitive), intermediate, or resistant to a particular antibiotic by using a cutoff point. Cut off points are agreed upon values, published in guidelines of a reference body, such as the U.S. Clinical and Laboratory Standards Institute (CLSI), the British Society for Antimicrobial Chemotherapy (BSAC) or the European Committee on Antimicrobial Susceptibility Testing (EUCAST)..
These in vitro MICs are based on concentrations of antibiotics obtained in vivo (ie, in blood, serum, or CSF). However, these in vivo concentrations depend on arbitrary administered doses. General antibiotic MIC guidelines have been imposed on the basis of a consensus of the influence of main instigators (ie, politicians and pharmaceutical companies).
There have been major discrepancies between the recommendations from various European countries over the years, and between those from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the US Clinical and Laboratory Standards Institute (CLSI).
The first step in drug discovery is often the screening of a library drug candidate for MICs against bacteria of interest. As such, MICs are usually the starting point for larger preclinical evaluations of novel antimicrobial agents.
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