Calculate the Minimum Inhibitory Concentration (MIC) of antimicrobial agents from dilution assay data to determine the lowest concentration that inhibits microbial growth.
MIC Value
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Lowest Concentration in Series
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Highest Concentration in Series
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MIC Interpretation
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MIC is the lowest concentration of an antimicrobial agent that inhibits visible growth of a microorganism. It's a key parameter in determining antibiotic effectiveness and resistance patterns.
The MIC well is the first well in the dilution series where growth is completely inhibited (typically >90% inhibition compared to the positive control). Count wells from highest to lowest concentration.
Two-fold dilutions are most common for MIC testing as they provide good resolution while maintaining manageable concentration ranges. Use smaller dilution factors for more precise MIC determination.
The positive control validates that the organism can grow under test conditions. An OD₆₀₀ of 0.5-1.0 indicates healthy growth and ensures your MIC results are reliable.
Compare your MIC value to established breakpoints (susceptible, intermediate, resistant) for the specific organism-antibiotic combination. These breakpoints are published by organizations like CLSI or EUCAST.
Key factors include inoculum size, incubation conditions, medium composition, and reading time. Standardized protocols like CLSI M07 help ensure reproducible results.
Yes, the same principles apply to antifungal MIC testing, though specific protocols and breakpoints may differ. Ensure you follow appropriate guidelines for fungal testing.
Check your inoculum preparation, ensure proper mixing of dilutions, verify incubation conditions, and consider testing multiple replicates. Quality control strains can help validate your methodology.