Phenotypic and Genotypic Investigation of the Resistance of Pathogenic Bacteroides fragilis Group Bacteria to Carbapenems

Objective: Bacteroides fragilis, predominantly found in the intestinal microbiota, is one of the most frequently encountered anaerobic pathogens and exhibits resistance to many antimicrobials. The carbapenem-resistant B. fragilis (CR-BF) isolates have been reported in several countries recently with increasing global attention. The high frequency of CR-BF in our hospitalized patients has become an important problem. For this reason, B. fragilis isolated in our hospital need to be closely monitored for carbapenem resistance. Therefore, we aimed to determine carbapenem resistance in B. fragilis isolated from clinical samples and the presence of the cfiA gene, which encodes for carbapenemase. Methods: B. fragilis strains isolated from various clinical samples collected between January 2018 and December 2022 were included in the study. Identification of the isolates was performed using MALDI-TOF MS. The susceptibility testing for meropenem and imipenem was determined by the agar dilution method. The cfiA gene was detected by PCR. Results: A total 89 B. fragilis strains were studied, mostly from intra-abdominal abscesses (31%) and blood cultures (27%). Susceptibility rates for meropenem and imipenem were 85.4% and 89%, respectively. Notably, 12 out of 13 cfiA gene-positive isolates were resistant, suggesting this gene as a marker for carbapenem resistance. However, resistance in one cfiA-negative isolates implies alternative resistance mechanisms. Conclusion: Routine anaerobic culture, determination of antibiotic susceptibility profiles of isolates, and close monitoring are crucial for managing infections. Regular antimicrobial susceptibility testing helps predict the risk of developing carbapenem resistance, assists clinicians in selecting appropriate antibiotics for empirical therapy, and improves treatment success rates.