Effects of medium and inoculum on antimicrobial susceptibility of anaerobic bacteria.

Abstract

Inhibitory activities of twofold dilutions of penicillin, chloramphenicol, tetracycline, and clindamycin were determined against two different inocula (104, 105) in parallel in supplemented brain-heart infusion agar, Brucella agar, and Mueller-Hinton agar. Incubation was in an anaerobic chamber for 48 hours. To compare MIC values of each antibiotic by medium and inoculum size, ![Graphic][1] was determined and averages were calculated. In general, MIC values in brain-heart infusion agar were almost twice as great as those in Mueller-Hinton agar; in general, MIC values in Mueller-Hinton agar with inocula of 105 were almost twice those with 104. Results with Brucella agar generally were intermediate between results with the other media. These differences, however, were not sufficiently great to alter the clinical interpretation of the results in terms of resistance or susceptibility of the strains tested. [1]: /embed/inline-graphic-1.gif