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Antimicrob Agents Chemother. 1977 April; 11(4): 605-608
Copyright © 1977 American Society for Microbiology. All Rights Reserved.

Penicillin Resistance and Penicillinase Production in Clinical Isolates of Bacteroides melaninogenicus

¹ Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55901

ABSTRACT

The minimum inhibitory concentrations (MIC) of penicillin and six other antimicrobials were determined for 50 clinical isolates of Bacteroides melaninogenicus. Agar dilution susceptibilities were performed using supplemented brucella blood agar and the proposed National Committee for Clinical Laboratory Standards standard method for anaerobes; results with the two methods were comparable. A penicillin concentration 0.8 µg/ml was needed to inhibit 56% of the isolates, whereas 100% were susceptible to 0.1 µg of clindamycin per ml. All isolates with penicillin MIC values 0.8 µg/ml produced ß-lactamase using a slide method. A micro-iodometric assay was used to quantitate ß-lactamase production in six isolates. The ß-lactamase activity of B. melaninogenicus was comparable to that of a Staphylococcus aureus isolate but was not inducible, and the specific amount produced correlated only partially with penicillin MIC values. A clinical review of patients from whom the ß-lactamase-producing strains of B. melaninogenicus were isolated did not suggest any increased virulence in these strains or an unexpectedly poor clinical response to appropriate therapy.

¹ Present address: Microbiology Laboratory, Division of Laboratory Medicine, Barnes Hospital, St. Louis, MO 63110.

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