Sensitivity of Bacteroides species to modern antimicrobial preparations

Strains of Bacteroides fragilis group isolated from peritoneal pus were tested for susceptibility to cefalotin, cefamandole, cefoxitin, clindamycin and metronidazole. Clindamycin and metronidazole were found to display the lowest MIC and MBC values. The median serum level of these antimicrobials was 2-4 times as high as the MIC effective against 100% of strains. The most active cephalosporin was the cephamycin derivative cefoxitin that inhibited 98% of strains at 16 mg/l which corresponds with the usual median serum level achieved at commonly recommended treatment regimens. The MICs of 16 mg/l to cefalotin and cefamandole were found in 9.8% and 3.7% of strains, respectively. These findings are consistent with data reported in the literature. Attention is also centered on the mode of antimicrobial action, principles of bacterial resistance and on factors which are co-responsible for the therapeutic effectiveness of the antimicrobials studied.