The minimum bactericidal concentration (MBC) is the lowest concentration of an antimicrobial agent that kills a bacterium, defined by preventing regrowth when the culture is transferred to antibiotic‑free media.
Explanation
MBC testing quantifies the bactericidal activity of antimicrobials. It is typically performed after a minimum inhibitory concentration (MIC) determination using a broth dilution method. Tubes or wells showing no visible growth are subcultured onto agar plates without antibiotic. The lowest concentration at which no growth occurs on the subculture indicates that ≥99.9 % of the original bacterial inoculum has been killed; this value is recorded as the MBC.
MBC values help differentiate bacteriostatic and bactericidal agents. While the MIC measures the lowest concentration that inhibits visible growth, the MBC measures killing. Agents with MBCs close to their MICs are considered bactericidal; those with much higher MBCs are bacteriostatic. Determining MBC is important for treating serious infections such as endocarditis or in immunocompromised patients where bactericidal therapy is preferred.
Determination and Applications
- MBC is determined by subculturing broth from MIC assays onto antibiotic‑free agar to identify the concentration that kills ≥99.9 % of bacteria.
- Concentrations below the MBC may merely suppress growth; understanding this threshold helps distinguish bactericidal from bacteriostatic drugs.
- MBC testing guides clinicians in selecting antibiotics for infections where bacterial eradication is critical, such as bloodstream infections and meningitis.
- Researchers use MBC data to evaluate the killing efficacy of new antimicrobial compounds and to study synergistic combinations.
MBC determination complements MIC testing, providing insight into the bactericidal properties of antimicrobial agents. It informs therapeutic decisions and supports the development of effective antimicrobial regimens.
Related Terms: MIC, Bactericidal, Broth Dilution, Antimicrobial Susceptibility, Minimum Inhibitory Concentration