What is the primary difference between MIC and MBC in antimicrobial susceptibility testing?

What is the primary difference between MIC and MBC in antimicrobial susceptibility testing?

• A. MIC is the lowest concentration that inhibits visible growth; MBC is the lowest concentration that kills a defined proportion of the initial inoculum (usually 99.9%).
• B. MIC measures bactericidal activity, MBC measures growth inhibition.
• C. MIC is the minimum bactericidal concentration, MBC is the minimum inhibitory concentration.
• D. MIC and MBC both measure inhibition but at different temperatures.

Answer: (A)

MIC and MBC describe two different antimicrobial effects on a microorganism. The minimum inhibitory concentration is the smallest amount of drug that stops visible growth after a standard incubation, so it reflects inhibition of growth rather than killing. The minimum bactericidal concentration is the smallest amount that kills a defined proportion of the initial inoculum, typically about 99.9%. To determine MBC, you take samples from the growth-inhibited cultures and plate them on drug-free media to see if viable cells can form colonies; if very few or none grow, that drug concentration is considered bactericidal. In practice, MIC and MBC are related but not identical—some drugs are bactericidal at concentrations near the MIC, while others require much higher concentrations to achieve killing.

MIC and MBC describe two different antimicrobial effects on a microorganism. The minimum inhibitory concentration is the smallest amount of drug that stops visible growth after a standard incubation, so it reflects inhibition of growth rather than killing. The minimum bactericidal concentration is the smallest amount that kills a defined proportion of the initial inoculum, typically about 99.9%. To determine MBC, you take samples from the growth-inhibited cultures and plate them on drug-free media to see if viable cells can form colonies; if very few or none grow, that drug concentration is considered bactericidal. In practice, MIC and MBC are related but not identical—some drugs are bactericidal at concentrations near the MIC, while others require much higher concentrations to achieve killing.