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.
Keywords: anaerobe, Bacteroides fragilis , carbapenem resistance, clinical characteristics