Diversity of antimicrobial resistance genes in Bacteroides and Parabacteroides strains isolated in Germany.

Objectives: Bacteroides spp. are normal constituents of the human intestinal microflora, but they are also able to cause severe diseases. The aim of this study was to determine the diversity of antibiotic resistance genes found in phenotypically resistant Bacteroides and Parabacteroides strains.

Methods: A total of 71 phenotypically resistant Bacteroides spp. from human clinical specimens were screened for the antibiotic resistance genes cfiA, tetQ, tetM, tet36, cepA, cfxA, nim, ermG, ermF, bexA, bla, bla, bla, bla and bla. The presence of these genes was compared with phenotypic resistance to ampicillin/sulbactam, cefoxitin, ceftolozane/tazobactam, piperacillin/tazobactam, imipenem, meropenem, meropenem/vaborbactam, clindamycin, moxifloxacin, tigecycline, eravacycline and metronidazole.

Results: tetQ was the most frequently detected gene, followed by cfiA, ermF, cfxA, ermG, cepA, nim and bexA. None of the strains were positive for tetM, tet36, bla, bla, bla, bla or bla. Resistance to the tested β-lactams was mainly linked to the presence of the cfiA gene. Clindamycin resistance correlated with the presence of the genes ermG and ermF. The bexA gene was found in six strains, but only two of them were resistant to moxifloxacin. Tigecycline and eravacycline showed good activities despite the frequent occurrence of tetQ. The nim gene was detected in six isolates, five of which were resistant to metronidazole.

Conclusion: The findings of our study support the general belief that antimicrobial resistance within Bacteroides should be taken into consideration. This underlines the necessity of reliable routine antimicrobial susceptibility test methods for anaerobic bacteria and the implementation of antimicrobial surveillance programmes worldwide.