Determinants of resistance in Bacteroides fragilis strains according to recent Brazilian profiles of antimicrobial susceptibility.

Susceptibility profiles of 99 Bacteroides fragilis strains for 9 antimicrobial agents were defined by using an agar dilution method. The isolates were uniformly susceptible to imipenen and metronidazole. All isolates were resistant to ampicillin. The resistance rates to amoxicillin/clavulanate, cefoxitin, cefotaxime, chloramphenicol, clindamycin and tetracycline were 3.0, 12.1, 15.1, 1.0, 18.2 and 75.7%, respectively. Sixteen strains showed reduced susceptibility to metronidazole (MIC 2-4 mg/L) but none had nim genes using PCR. All strains were also investigated for the presence of cepA, cfiA, cfxA, ermF and tetQ genes by PCR methodology and 92.9, 4.9, 24.2, 2 and 64.6% of the strains were respectively found positive. These results reflect the importance of surveys of susceptibility profiles and the relevance of detecting major genetic determinants to monitor the dissemination of these genes.