The minimum bactericidal concentration (MBC) of an antibiotic is defined as the lowest concentration that kills what percentage of the original bacterial inoculum?
- A 50% of the original inoculum
- B 99.9% of the original inoculum (3-log reduction) ✓
- C 99% of the original inoculum (2-log reduction)
- D 100% of the original inoculum (complete sterility)
Correct answer: B. 99.9% of the original inoculum (3-log reduction)
Explanation
MBC is the lowest concentration of an antimicrobial agent that kills ≥99.9% (a 3-log reduction or 1000-fold reduction) of the original bacterial inoculum, indicating bactericidal activity. The MIC only inhibits growth (bacteriostatic threshold) and does not define killing. Complete sterility is not the standard criterion; the 99.9% threshold is the internationally accepted definition.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.