The minimum bactericidal concentration (MBC) of an antimicrobial agent is defined as:
- A The lowest concentration that kills 99.9 percent of the original bacterial inoculum on subculture ✓
- B The lowest concentration that inhibits 50 percent of bacterial isolates tested
- C The lowest concentration preventing visible growth on the agar plate
- D The lowest concentration producing a zone of inhibition around the antibiotic disk
Correct answer: A. The lowest concentration that kills 99.9 percent of the original bacterial inoculum on subculture
Explanation
The MBC is determined by subculturing tubes from an MIC broth dilution series onto drug-free agar; the lowest concentration yielding no growth, or killing at least 99.9 percent of the initial inoculum, is the MBC. Option C restates the MIC, which permits survival of a small residual population and is therefore not bactericidal. Option D refers to disk diffusion zones, which give qualitative category results rather than cidal endpoints, and option B describes an EC50 style population statistic.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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