In vitro synergy and potentiation between cefotaxime and desacetylcefotaxime against clinical isolates of Bacteroides

A broth microdilution checkerboard system was used to determine the activity of cefotaxime (CTX) and desacetylcefotaxime (des-CTX), alone and in combination, against 92 clinical isolates of Bacteroides species. Overall, CTX was only marginally more active than the metabolite. Resistance to both compounds was found among B. fragilis group, B. disiens, B. bivius, and B. capillosus. The combination of CTX with des-CTX resulted in a marked reduction of the MICs greater than or equal to fourfold for 82% of the strains tested. In addition, complete or partial synergy was noted with the combination against 85% of the strains tested. The ratio of CTX to des-CTX at the inhibitory endpoints varied widely, but in 75% of the cases it was 2:1 to 1:2 parts CTX to des-CTX.