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Antimicrob Agents Chemother. 1979 August; 16(2): 214-216
Copyright © 1979, American Society for Microbiology. All Rights Reserved.

Importance of Medium in Demonstrating Penicillin Tolerance by Group B Streptococci

Kwang Sik Kim1, Robert N. Yoshimori2, David T. Imagawa1,3 and Bascom F. Anthony1

1 Department of Pediatrics, Los Angeles County Harbor/UCLA Medical Center, University of California at Los Angeles School of Medicine, Torrance, California 90509
2 Department of Pathology, Los Angeles County Harbor/UCLA Medical Center, University of California at Los Angeles School of Medicine, Torrance, California 90509
3 Department of Microbiology, Los Angeles County Harbor/UCLA Medical Center, University of California at Los Angeles School of Medicine, Torrance, California 90509

ABSTRACT

A total of 30 clinical isolates of group B streptococci were studied for penicillin tolerance in vitro. Minimal inhibitory and bactericidal concentrations of penicillin were determined simultaneously in three test media which have been used for group B streptococci, tryptose phosphate, Mueller-Hinton, and Todd-Hewitt broths, using a logarithmic-phase inoculum of 105 colony-forming units per ml. Minimal inhibitory concentrations in the three media did not differ significantly. However, minimal bactericidal concentrations were significantly higher in tryptose phosphate broth (mean, 1.04 µg/ml) than in Mueller-Hinton broth (0.22 µg/ml) or Todd-Hewitt broth (0.15 µg/ml). Similarly, ratios of minimal bactericidal to minimal inhibitory concentrations were significantly greater in tryptose phosphate broth than in Mueller-Hinton or Todd-Hewitt broth. After incubation in tryptose phosphate broth for an additional 24 h, the minimal bactericidal concentration consistently fell to levels which were only twice or equal to the minimal inhibitory concentration. This study illustrates the importance of the medium in the demonstration of penicillin tolerance and of controlling laboratory variables in the susceptibility testing of group B streptococci with penicillin.

Antimicrob Agents Chemother. 1979 August; 16(2): 214-216
Copyright © 1979, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Steinbrecher, U. P. (1981). Serious Infection in an Adult due to Penicillin-Tolerant Group B Streptococcus. Arch Intern Med 141: 1714-1715 [Abstract]  


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