Higher Prevalence of Multi-Antimicrobial Resistant Bacteroides spp. Strains Isolated at a Tertiary Teaching Hospital in China

PURPOSE: The study investigates the molecular epidemiology of multi-drug resistant (MDR) Bacteroides spp. isolates and the clinical characteristics of the patients. MATERIALS AND METHODS: Bacteroides spp. clinical strains were identified through MALDI-TOF MS and VITEK-2 anaerobes and corynebacterium (ANC) cards. A broth microdilution method was employed to detect the antimicrobial sensitivities of Bacteroides spp. isolates. PCR was used to detect the resistance genes, including cfxA, cepA, cfiA, ermF, nim, as well as the upstream insertion sequence (IS) element of the cfiA gene. The effects of broad-spectrum efflux pump inhibitors (EPIs) on the minimal inhibitory concentration (MICs) of cefoxitin, moxifloxacin, and imipenem for MDR Bacteroides spp. were investigated. RESULTS: The total resistance rates of 115 Bacteroides spp. isolates to cefoxitin, moxifloxacin, clindamycin, metronidazole, imipenem and meropenem were 4.3%, 16.5%, 80.0%, 5.2%, 13.9% and 13.9%, respectively. The positive rates of carbapenem resistance gene cfiA were 38.9% and 8.6% for B. fragilis and non-B. fragilis isolates, respectively. The isolation rate of MDR isolates reached up to 18.26% (21/115), and the isolation rate among the gastrointestinal cancer patients was significantly higher when compared to the non-gastrointestinal cancer patients (52.38%/26.08%, P = 0.006). Furthermore, MDR isolates were more likely to be isolated from the patients exposed to cephalosporins 3 months before Bacteroides spp. isolation (76.19%/31.52%, P = 0.000). CONCLUSION: The overall resistance rates of Bacteroides spp. isolates against multiple antimicrobials were at a high level, especially for B. fragilis. The CfiA gene carrying rate among B. fragilis isolates was as high as 38.9%, and its mediated carbapenem resistance was the major resistance mechanism for B. fragilis. The findings of this study imply that the real resistance tendency of Bacteroides spp. may be underestimated and need to be given more attention.