Antimicrobial Resistance Profile and Nim Gene Detection among Bacteroides fragilis Group Isolates in a University Hospital in South India

INTRODUCTION: Members of Bacteroides fragilis group are the most frequently isolated anaerobic pathogens in the clinical laboratory from diverse infection sites. The objective of this study was to characterize B. fragilis isolates from various clinical specimens, to analyze their susceptibility profile toward most common anti-anaerobic antimicrobials, and to study the frequency of nim gene determining resistance to nitroimidazoles. METHODS: Specimens processed for anaerobic culture between January 2013 and December 2015 were analyzed. Isolates of B. fragilis group were identified and speciated by mass spectrometry. β-lactamase production was detected using nitrocefin disks. Agar dilution and antimicrobial gradient diffusion methods were performed to study their susceptibility profile. The isolates were screened for nim gene by conventional gel-based polymerase chain reaction. RESULTS: A total of 57 isolates of B. fragilis group were studied. The commonly isolated species was B. fragilis (73.7%), followed by Bacteroides thetaiotaomicron (8.8%), Bacteroides vulgatus (8.8%), and others. Most of the isolates were recovered from deep-seated abscesses (47.4%). All isolates were found to be β-lactamase producers. Metronidazole (Mtz) resistance was observed in 4 (7%) isolates. Higher rate of resistance was observed toward clindamycin (31.6%). None of the isolates tested were found resistant to chloramphenicol, piperacillin-tazobactam, and meropenem. nim genes were present in 4 (11.4%) B. fragilis isolates (n = 35). CONCLUSIONS: Resistance to the most commonly used empirical anti-anaerobic drugs including Mtz was noted in the isolates of B. fragilis group. Routine anaerobic cultures when indicated and continual surveillance of antimicrobial resistance among the anaerobic bacterial pathogens is essential.