16
µg/mL
0.5
µg/mL
16
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16
µg/mL
0.5
µg/mL
16
×
The MIC Calculator determines the Minimum Inhibitory Concentration of an antibiotic based on a twofold serial dilution series. MIC is the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism, and it is the reference standard for susceptibility testing in clinical microbiology.
Enter the highest concentration in your dilution series and the well number where growth is first inhibited to determine the MIC value.
In a standard MIC assay, the antibiotic is serially diluted twofold across wells. The concentration in any well is:
Concentration = Starting Concentration / 2^(Well Number − 1)
Well 1 has the highest concentration (undiluted), Well 2 is half, Well 3 is a quarter, and so on. The MIC is the concentration in the first well (lowest concentration) that shows no visible bacterial growth.
Inputs
Results
Starting at 256 µg/mL, the 5th well contains 16 µg/mL. If growth is inhibited here but not in well 6 (8 µg/mL), the MIC is 16 µg/mL.
Inputs
Results
With a starting concentration of 64 µg/mL, the 3rd well (16 µg/mL) is the MIC. An MIC above 2 µg/mL for vancomycin against Staphylococcus would indicate reduced susceptibility.
MIC values are compared to breakpoints established by organizations like CLSI or EUCAST to categorize organisms as susceptible, intermediate, or resistant. A low MIC means the organism is easily killed by the drug. MIC helps clinicians choose appropriate antibiotics and dosing regimens for treating infections.
Twofold (doubling) dilutions are the international standard because they provide a consistent, reproducible, and practical method for testing a wide range of concentrations. Using twofold steps means each well differs by a factor of 2, giving a logarithmic range that efficiently covers several orders of magnitude.
MIC (Minimum Inhibitory Concentration) is the lowest concentration that prevents visible growth but does not necessarily kill the bacteria. MBC (Minimum Bactericidal Concentration) is the lowest concentration that kills 99.9% of the bacteria. MBC is determined by subculturing from MIC wells onto drug-free plates.
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