Abstract
MBC testing of clindamycin, methicillin, cephalothin, gentamicin, and vancomycin with 67 clinical isolates of Staphylococcus aureus was examined by both standard macrodilution tubes and commercial microdilution trays. Standard macrodilution failed to give reproducible (99.9% killing) MBC results, even when a strictly defined protocol was followed. Continuous shaking during incubation resulted in regrowth of more colonies than did stationary incubation. Vortexing of incubated tubes before subculture resulted in regrowth of more colonies than did careful transfer of the contents to sterile tubes before vortexing and subculture. No significant difference in MBCs was demonstrated by the use of log-phase versus stationary-phase inocula. Use of the multiprong inoculator for subculture from commercial microdilution trays was unsatisfactory because, although antibiotics evaluated were inactivated by subculture to a pH 5.5 agar plate coated with a beta-lactamase solution, the volume of broth transferred by the prongs was small and inconsistent, ranging from 0 to 3 microliter. Subcultures of commercial microdilution panels with a 1-microliter loop, 10-microliter pipette, and 100-microliter pipette were also evaluated. Results of MBC testing were most reproducible when the entire 100-microliter volume was aspirated from commercial microdilution wells after stirring and the contents of each well were spread over a separate sheep blood agar plate.
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- Barry A. L., Lasner R. A. In-vitro methods for determining minimal lethal concentrations of antimicrobial agents. Am J Clin Pathol. 1979 Jan;71(1):88–92. doi: 10.1093/ajcp/71.1.88. [DOI] [PubMed] [Google Scholar]
- Bradely J. J., Mayhall C. G., Dalton H. P. Incidence and characteristics of antibiotic-tolerant strains of Staphylococcus aureus. Antimicrob Agents Chemother. 1978 Jun;13(6):1052–1057. doi: 10.1128/aac.13.6.1052. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Goessens W. H., Fontijne P., Michel M. F. Factors influencing detection of tolerance in Staphylococcus aureus. Antimicrob Agents Chemother. 1982 Sep;22(3):364–368. doi: 10.1128/aac.22.3.364. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Harwick H. J., Weiss P., Fekety F. R., Jr Application of microtitration techniques to bacteriostatic and bactericidal antibiotic susceptibility testing. J Lab Clin Med. 1968 Sep;72(3):511–516. [PubMed] [Google Scholar]
- Ishida K., Guze P. A., Kalmanson G. M., Albrandt K., Guze L. B. Variables in demonstrating methicillin tolerance in Staphylococcus aureus strains. Antimicrob Agents Chemother. 1982 Apr;21(4):688–690. doi: 10.1128/aac.21.4.688. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mayhall C. G., Apollo E. Effect of storage and changes in bacterial growth phase and antibiotic concentrations on antimicrobial tolerance in Staphylococcus aureus. Antimicrob Agents Chemother. 1980 Nov;18(5):784–788. doi: 10.1128/aac.18.5.784. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mayhall C. G., Medoff G., Marr J. J. Variation in the susceptibility of strains of Staphylococcus aureus to oxacillin, cephalothin, and gentamicin. Antimicrob Agents Chemother. 1976 Oct;10(4):707–712. doi: 10.1128/aac.10.4.707. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Prober C. G., Dougherty S. S., Vosti K. L., Yeager A. S. Comparison of a micromethod for performance of the serum bactericidal test with the standard tube dilution method. Antimicrob Agents Chemother. 1979 Jul;16(1):46–48. doi: 10.1128/aac.16.1.46. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Taylor P. C., Schoenknecht F. D., Sherris J. C., Linner E. C. Determination of minimum bactericidal concentrations of oxacillin for Staphylococcus aureus: influence and significance of technical factors. Antimicrob Agents Chemother. 1983 Jan;23(1):142–150. doi: 10.1128/aac.23.1.142. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zinner S. H., Husson M., Klastersky J. Effect of mixing on rifampin bactericidal activity against staphylococci. Antimicrob Agents Chemother. 1981 Aug;20(2):267–269. doi: 10.1128/aac.20.2.267. [DOI] [PMC free article] [PubMed] [Google Scholar]