First National Survey of Antibiotic Susceptibility of the Bacteroides fragilis Group: Emerging Resistance to Carbapenems in Argentina

Abstract

ABSTRACTThe antibiotic susceptibility rates of 363 clinicalBacteroides fragilisgroup isolates collected from 17 centers in Argentina during the period from 2006 to 2009 were as follows: piperacillin-tazobactam, 99%; ampicillin-sulbactam, 92%; cefoxitin, 72%; tigecycline, 100%; moxifloxacin, 91%; and clindamycin, 52%. No metronidazole resistance was detected in these isolates during this time period. Resistance to imipenem, doripenem, and ertapenem was observed in 1.1%, 1.6%, and 2.3% ofB. fragilisgroup strains, respectively.B. fragilisspecies showed a resistance profile of 1.5% to imipenem, 1.9% to doripenem, and 2.4% to ertapenem. This is the first report of carbapenem resistance in Argentina. ThecfiAgene was present in 8 out of 23 isolates, all of them belonging to theB. fragilisspecies and displaying reduced susceptibility or resistance to carbapenems (MICs ≥ 4 μg/ml). Three out of eightcfiA-positive isolates were fully resistant to carbapenems, while 5 out of 8 isolates showed low-level resistance (MICs, 4 to 8 μg/ml). The inhibition by EDTA was a good predictor of the presence of metallo-β-lactamases in the fully resistantB. fragilisstrains, but discrepant results were observed for low-level resistant isolates.B. fragiliswas more susceptible to antimicrobial agents than otherBacteroidesspecies.Bacteroides vulgatusspecies was the most resistant to ampicillin-sulbactam and piperacillin-tazobactam, andB. thetaiotaomicron/ovatusstrains showed the highest level of resistance to carbapenems, with an unknown resistance mechanism.B. vulgatusand the uncommon non-Bacteroides fragilisspecies were the most resistant to moxifloxacin, showing an overall resistance rate of 15.1%.