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 nongastrointestinal 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.

Background: The antimicrobial resistance of Bacteroides spp. isolates is reported to be increasing among different districts around the world, and few reports found that multi-antimicrobial resistant strains emerged. However, less is known about the prevalence of multi-antimicrobial resistant isolates in China, especially for carbapenem resistance. Methods: Bacteroides spp. clinical strains were isolated from inpatients at a 3000 bed tertiary teaching hospital , and were identified by MALDI-TOF MS and VITEK-2 anaerobes and corynebacterium (ANC) card. Broth microdilution method was employed to detect the antimicrobial sensitivities of Bacteroides spp. isolates and PCR method was used to detect the resistance genes, including cfxA, cepA, cfiA, ermF and nim. The upstream insertion sequence (IS) element of cfiA gene was further detected and verified. Results: Among 115 Bacteroides spp. strains enrolled in this study, 80 isolates were Bacteroides fragilis and 35 isolates were non-Bacteroides fragilis. The total resistance rates of 115 Bacteroides spp. isolates to ampicillin/sulbactam, amoxicillin/clavulanic, cefoxitin, piperacillin, piperacillin/tazobactam, moxifloxacin, clindamycin, metronidazole, imipenem and meropenem were 22.6%, 19.6%, 3.5%, 27.8%, 8.7%, 16.5%, 80.0%, 5.2%, 13.9% and 13.9% , respectively. Except cefoxitin and moxifloxacin, the resistance rates of B. fragilis isolates to the above antibiotics were all higher than those of non-B. fragilis isolates. The positive rates of carbapenem resistance gene cfiA were 38.9% and 8.6% for B. fragilis and non-B. fragilis isolates, respectively. For 15 carbapenem resistant B. fragilis isolates, the co-carrying rates of carbapenem resistance gene cfiA and its upstream IS element were 86.7% (13/15). Conclusions: The overall resistance rates of Bacteroides spp. isolates toward multiple antibiotics were at a higher level, especially for B. fragilis. CfiA gene carrying rate among B. fragilis isolates was high up to 38.9% and its mediated carbapenem resistance was a major resistance mechanism for B. fragilis. The findings of this study imply that the actual resistance tendency of Bacteroides spp. may be underestimated and need to be given more attention to.