Abstract
A novel and time-saving method for assessing bactericidal activities of β-lactam antibiotics on agar plates is described. Minimal inhibitory concentrations (MICs) were determined by the agar dilution method. A potent β-lactamase solution was sprayed onto the plates to inactivate the antibiotic. After further incubation at 37°C overnight, the minimal concentration at which no visible growth occurred on the plates was defined as minimal bactericidal concentration (MBC). With undiluted culture as the inoculum, strains of Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae showed a marked increase in MBC values compared with the values of MIC. There was a marked decrease in both the MICs and MBCs with diminution of inoculum size. The two concentrations were almost the same when the inoculum size was decreased to a 10−4 dilution. In contrast, MIC and MBC for enterococci showed no marked decrease with decrease in inoculum size. Although the present study was performed with β-lactamase-unstable penicillins and cephalosporins, the method can be applicable with any β-lactam antibiotic if optimal and potent enzymes are available.
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- Beaty H. N., Turck M., Petersdorf R. G. Activity of broad-spectrum antibiotics against enterococci and their efficacy in enterococcal endocarditis. Ann N Y Acad Sci. 1967 Sep 27;145(2):464–472. doi: 10.1111/j.1749-6632.1967.tb50246.x. [DOI] [PubMed] [Google Scholar]
- Bergeron M. G., Brusch J. L., Barza M., Weinstein L. Bactericidal activity and pharmacology of cefazolin. Antimicrob Agents Chemother. 1973 Oct;4(4):396–401. doi: 10.1128/aac.4.4.396. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ericsson H. M., Sherris J. C. Antibiotic sensitivity testing. Report of an international collaborative study. Acta Pathol Microbiol Scand B Microbiol Immunol. 1971;217(Suppl):1+–1+. [PubMed] [Google Scholar]
- HAMILTON-MILLER J. M., SMITH J. T., KNOX R. POTENTIATION OF PENICILLIN ACTION BY INHIBITION OF PENICILLINASE. Nature. 1964 Feb 29;201:867–868. doi: 10.1038/201867a0. [DOI] [PubMed] [Google Scholar]
- Masuda G. Studies on bactericidal activities of beta-lactam antibiotics on agar plates: the correlation with the antibacterial activities determined by the conventional methods. J Antibiot (Tokyo) 1976 Nov;29(11):1237–1240. doi: 10.7164/antibiotics.29.1237. [DOI] [PubMed] [Google Scholar]
- Masuda G., Tomioka S., Hasegawa M. Detection of beta-lactamase production by gram-negative bacteria. J Antibiot (Tokyo) 1976 Jun;29(6):662–664. doi: 10.7164/antibiotics.29.662. [DOI] [PubMed] [Google Scholar]
- Simon H. J. Antimicrobial susceptibility of group D hemolytic streptococci (enterococci). Am J Med Sci. 1967 Jan;253(1):14–18. doi: 10.1097/00000441-196701000-00004. [DOI] [PubMed] [Google Scholar]
- Turck M., Clark R. A., Beaty H. N., Holmes K. K., Karney W. W., Reller L. B. Cefazolin in the treatment of bacterial pneumonia. J Infect Dis. 1973 Oct;128(Suppl):S382–S385. doi: 10.1093/infdis/128.supplement_2.s382. [DOI] [PubMed] [Google Scholar]