Careful control and standardization is required for intra- and interlaboratory reproducibility as results may be significantly influenced by the method used. The MIC is a guide for the clinician to the susceptibility of the organism to the antimicrobial agent and aids treatment decisions. The lowest concentration of an antimicrobial agent (in mg/L) that, under defined in vitro conditions, prevents the appearance of visible growth of a microorganism within a defined period of time, is known as the MIC.
In dilution tests microorganisms are tested for their ability to produce visible growth on a series of agar plates (agar dilution) or in broth (broth dilution) containing dilutions of the antimicrobial agent. MIC methods are used in resistance surveillance, the comparative testing of new agents, to establish the susceptibility of organisms that give equivocal results in disc tests, for tests on organisms where disc tests may be unreliable and when a quantitative result is required for clinical management. The tests are also important in resistance surveillance, epidemiological studies of susceptibility and in comparisons of new and existing agents.ĭilution methods are used to determine the minimum inhibitory concentrations (MICs) of antimicrobial agents and are the reference methods for antimicrobial susceptibility testing.
In vitro susceptibility tests are performed on microorganisms suspected of causing disease, particularly if the organism is thought to belong to a species that may exhibit resistance to frequently used antimicrobial agents.
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