The minimum bactericidal concentration (MBC) is defined as the lowest concentration that kills at least what percent of the original inoculum?

The minimum bactericidal concentration (MBC) is defined as the lowest concentration that kills at least what percent of the original inoculum?

• A. 95.5%
• B. 97%
• C. 99.9%
• D. 100%

Answer: (C)

The MBC is the lowest concentration of an antimicrobial that kills at least 99.9% of the original bacterial population. That 99.9% kill corresponds to about a 3-log reduction in viable cells (for example, from 10^6 to 10^3 CFU/mL). Among the options, 99.9% best fits this standard: it reflects a true bactericidal effect, whereas 95.5% or 97% are lower levels of kill, and 100% would imply total elimination—which isn’t the defined criterion for the MBC.

The MBC is the lowest concentration of an antimicrobial that kills at least 99.9% of the original bacterial population. That 99.9% kill corresponds to about a 3-log reduction in viable cells (for example, from 10^6 to 10^3 CFU/mL). Among the options, 99.9% best fits this standard: it reflects a true bactericidal effect, whereas 95.5% or 97% are lower levels of kill, and 100% would imply total elimination—which isn’t the defined criterion for the MBC.