A 5-YEAR MULTICENTER STUDY OF THE SUSCEPTIBILITY OF THE BACTEROIDES-FRAGILIS GROUP ISOLATES TO CEPHALOSPORINS, CEPHAMINS, PENICILLINS, CLINDAMYCIN, AND METRONIDAZOLE IN THE UNITED-STATES

Over 2800 clinical strains of the Bacteroides fragilis group were coll ected during a 5-year period from ten geographically separate sites an d tested for their susceptibility to various antimicrobial agents usin g a broth microdilution method. Among the cephalosporins, ceftizoxime was the most active (13% resistance) and importantly exhibited relativ ely equal activity against both B. fragilis species and non-B. fragili s species. Cefotaxime exhibited similar activity with an overall resis tance rate of 18%. Both ceftriaxone and cefoperazone were appreciably less active cephalosporins especially against non-B. fragilis species. With regard to cephamycins, cefoxitin (MIC(90), 32 mu g/ml) was move active than cefotetan (MIC(90) greater than or equal to 256 mu g/ml) a nd cefmetazole (MIC(90), 64 mu g/ml). Non-B. fragilis species were hig hly resistant to cefotetan and cefmetazole. Imipenem was highly active against all strains with the exception of four strains of B. fragilis . Ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobact am, and cefoperazone-sulbactam were all highly active with resistance rates <2%. No resistance was detected to metronidazole, whereas 14% of isolates were resistant to clindamycin. When compared with other stud ies, these findings underscore the wide variability in susceptibility patterns reported nationwide and the need to continue monitoring these patterns to aid in choosing the most active compounds for therapy.