Antimicrobial-resistant Bacteroides fragilis in Thailand and their inhibitory effect in vitro on the growth of Clostridioides difficile

Objectives The aim of this study was to investigate antimicrobial-resistant Bacteroides fragilis in Thailand and possible effects of such strains on human health and disease. Methods Phenotypic antimicrobial susceptibility testing was performed on 17 clinical B. fragilis isolates. The genome of one isolate was sequenced and analysed to explore its resistance genotype. An in vitro growth assay was conducted to evaluate the inhibitory effect of B. fragilis on Clostridioides difficile. Results There was a high prevalence of clindamycin (71%), meropenem (47%) and moxifloxacin (29%) resistance. Most strains remained susceptible to metronidazole, but one had high-level metronidazole resistance conferred by a nimD-containing plasmid. B. fragilis displayed an in vitro inhibitory effect on the growth of C. difficile and a drug-resistant strain retained this inhibition in the presence of clindamycin. Conclusions Antimicrobial resistance was seen in Thai B. fragils isolates, which may help protect the host against C. difficile infection