LONGITUDINAL-STUDY OF SUSCEPTIBILITIES OF SPECIES OF THE BACTEROIDES-FRAGILIS GROUP TO 5 ANTIMICROBIAL AGENTS IN 3 MEDICAL-CENTERS

A total of 579 clinical isolates of the Bacteroides fragilis group col lected from three Canadian hospitals were tested for susceptibility to five antimicrobial agents by using an agar dilution method. During th e 4-year survey, isolates from intra-abdominal infections were collect ed from the following sites: abdominal abscesses (48%), peritoneal flu id (39%), blood (10%), and bile (3%). B. fragilis was the most prevale nt species (35.4%), followed by B. thetaiotaomicron (19.2%), B. ovatus (15.9%), and B. vulgatus (11%). No metronidazole- or imipenem-resista nt strains were found during the survey. Resistance profiles varied am ong the different species tested: 7.8, 2.9, and 7.3% of B. fragilis st rains (n = 205) and 68.1, 17.2, and 9.4% of non-B. fragilis strains (n = 373) were resistant to cefotetan, cefoxitin, and clindamycin, respe ctively. B. fragilis and B. vulgatus demonstrated lower resistance rat es than B. thetaiotaomicron, B. ovatus, B. distasonis, and B. caccae. During the study, rates of resistance to cefotetan and clindamycin flu ctuated but rates of resistance to cefoxitin increased, particularly a t one center. These data indicate a need to determine the susceptibili ty patterns of the B. fragilis group periodically at each hospital.