Carbapenem resistance in enterotoxigenic Bacteroides fragilis isolated from colonoscopy candidates

The present study aimed to determine the carbapenem resistance among Enterotoxigenic Bacteroides fragilis (ETBF) isolated from patients candidates to colonoscopy in Shiraz, Iran. A total of 201 stool samples were gathered from 201 patients. The detection of B. fragilis group, B. fragilis, and ETBF was performed using a PCR assay targeting bfg, 16S rRNA, and bft genes, respectively. The enterotoxin isotype-encoding genes (bft-1, bft-2, and bft-3) were detected in ETBF using a PCR assay. Antimicrobial susceptibility profile of ETBF against imipenem and meropenem was determined using the Liofilchem® MIC Test Strips. The Ana-CIM assay was used for the phenotypic detection of carbapenemase production in ETBF strains. The presence of the cfiA and insertion sequence (IS) encoding genes (IS1186, IS1187, IS1188, IS942) was determined using a PCR assay. Overall, 71.64%, 33.83%, and 20.4% of patients were positive for B. fragilis group, B. fragilis, and ETBF, respectively. 28 (68.3%) tested positive for the bft-1 gene, whereas only one isolate (2.4%) contained the bft-3 gene. 80% (n = 4/5) of patients with polyp in sigmoid colon + colorectal polyp and 72.7% (n = 8/11) of patients with hemorrhoids were positive to ETBF. 2.4% and 48.8% of ETBF isolates were resistant to imipenem and meropenem, respectively. Out of the 41 ETBF isolates, 28 (68.3%) were positive for carbapenemase production. 46.3% (n = 18/41) of ETBF were positive for the cfiA gene. 27 isolates (96.4%) harbored the IS1187 gene. Resistance rates of ETBF to meropenem were high. Most patients with a polyp in the sigmoid colon, colorectal polyp, and hemorrhoids were positive for ETBF.