Clinico-microbiological profile of Bacteroides fragilis with focus on molecular detection of emerging resistance

Background & objective: Bacteroides fragilis is a Gram-negative anaerobic opportunistic pathogen which is managed by empirical anaerobic coverage as a hospital norm. However, with rising reports of resistance among B. fragilis strains, antibiotic susceptibility testing for this pathogen may be the only way to understand the magnitude of the problem. This study aimed to characterize resistance patterns among clinical isolates and identify resistance genes. Methods: A prospective observational study was conducted which included all samples requesting anaerobic cultures within the study period. Minimum inhibitory concentration (MIC) was detected for metronidazole, clindamycin and chloramphenicol by agar dilution. E-test strips were used for imipenem and piperacillin, followed by polymerase chain reaction to detect nim and cfiA genes. Results: Among a total of 50 isolates, 94 per cent (47/50) were susceptible and six per cent (3/50) showed intermediate resistance to metronidazole. Susceptibility to clindamycin and piperacillin was noted in 70 and 50 per cent of strains; intermediate resistance in 14 and 2 per cent and resistance in 16 and 48 per cent, respectively. No resistance was observed for chloramphenicol and imipenem. Nim gene was found in 26 per cent (13/50) and cfiA gene was found in 52 per cent (26/50) of isolates. Isolates with high metronidazole MIC of 8-16 μg/ml were found to carry nim gene (χ2 test, P<0.001). Interpretation & conclusions: Rising resistance among B. fragilis is evident and there is a significant association between nim gene and metronidazole resistance. Improving awareness among clinicians is paramount in tackling AMR among these pathogens, as empirical anaerobic coverage may not be effective in all cases.