Minimum bactericidal concentration explained

The minimum bactericidal concentration (MBC) is the lowest concentration of an antibacterial agent required to kill a particular bacterium.^[1] It can be determined from broth dilution minimum inhibitory concentration (MIC) tests by subculturing to agar plates that do not contain the test agent. The MBC is identified by determining the lowest concentration of antibacterial agent that reduces the viability of the initial bacterial inoculum by ≥99.9%.^[2] The MBC is complementary to the MIC; whereas the MIC test demonstrates the lowest level of antimicrobial agent that inhibits growth, the MBC demonstrates the lowest level of antimicrobial agent that results in microbial death. This means that even if a particular MIC shows inhibition, plating the bacteria onto agar might still result in organism proliferation because the antimicrobial did not cause death. Antibacterial agents are usually regarded as bactericidal if the MBC is no more than four times the MIC.^{[3] [4]} Because the MBC test uses colony-forming units as a proxy measure of bacterial viability, it can be confounded by antibacterial agents which cause aggregation of bacterial cells. Examples of antibacterial agents which do this include flavonoids^[4] and peptides.^{[5] [6]}

Notes and References

1. Amyes S et al. Antimicrobial Chemotherapy: Pocketbook. CRC Press, 1996 Page 25
2. Book: [[Clinical and Laboratory Standards Institute|National Committee for Clinical Laboratory Standards]]. Methods for determining bactericidal activity of antimicrobial agents : approved guideline M26-A. National Committee for Clinical Laboratory Standards. Arthur L. Barry et. al.. 1999. 1-56238-384-1. 19. Wayne, PA. en. 1124514908. 18.
3. French GL . Bactericidal agents in the treatment of MRSA infections--the potential role of daptomycin . Journal of Antimicrobial Chemotherapy. 58 . 6 . 1107–17 . 2006 . 17040922 . 10.1093/jac/dkl393 .
4. Cushnie TP, Cushnie B, Echeverría J, Fowsantear W, Thammawat S, Dodgson JL, Law S, Clow SM . 2020 . Bioprospecting for antibacterial drugs: a multidisciplinary perspective on natural product source material, bioassay selection and avoidable pitfalls. Pharmaceutical Research . 37 . 7 . Article 125. 10.1007/s11095-020-02849-1. 32529587. 219590658 .
5. Suarez M, Haenni M, Canarelli S, Fisch F, Chodanowski P, Servis C, Michielin O, Freitag R, Moreillon P, Mermod N . Structure-function characterization and optimization of a plant-derived antibacterial peptide. Antimicrobial Agents and Chemotherapy . 2005 . 49 . 9 . 3847–3857 . 16127062 . 10.1128/AAC.49.9.3847-3857.2005 . 1195432.
6. Robert É, Lefèvre T, Fillion M, Martial B, Dionne J, Auger M. 2015 . Mimicking and understanding the agglutination effect of the antimicrobial peptide thanatin using model phospholipid vesicles. Biochemistry. 54 . 25 . 3932–41 . 10.1021/acs.biochem.5b00442. 26057537.