Complete genome sequence of cfr(B)-carrying Enterococcus raffinosus isolated from bile in a patient in Japan.

OBJECTIVES: Linezolid is an antibiotic used to treat infectious diseases caused by vancomycin-resistant enterococci and methicillin-resistant Staphylococcus aureus. Recently, Enterococcus Spp.-carrying mobile linezolid resistance genes were reported. Herein, we report the complete genome sequence of Enterococcus raffinosus JARB-HU0741, which was isolated from a bile sample of a patient in Japan on May 5, 2021, and carries a linezolid resistance gene, cfr(B). Nevertheless, this isolate was susceptible to linezolid. METHODS: Whole-genome sequencing was performed using HiSeq X FIVE (Illumina) and GridION (Oxford Nanopore Technologies). The sequence reads were assembled using Unicycler v0.4.8, and the complete genome was annotated using DFAST v1.2.18. Antimicrobial resistance genes were detected with Abricate v1.0.1, using the ResFinder database. The minimum inhibitory concentrations (MICs) were determined using broth microdilution and interpreted according to the guidelines of the Clinical and Laboratory Standards Institute. RESULTS: E. raffinosus JARB-HU0741 contained a 3 248 808-bp chromosome and a 1 156 277-bp megaplasmid. cfr(B) was present in the Tn6218-like transposon, which was inserted into a gene encoding a PRD domain-containing protein present in the megaplasmid, but the isolate was susceptible to linezolid (MIC, 0.5 µg/mL). The Tn6218-like transposon was similar to the Tn6218 of Clostridioides difficile Ox3196 and the Tn6218-like transposon of Enterococcus faecium UW11733; however, three genes encoding a topoisomerase, an S-adenosylmethionine-dependent methyltransferase, and a TetR family transcriptional regulator were present in the previous Tn6218- or Tn6218-like transposon. CONCLUSION: This is the first report of the complete genome sequence of E. raffinosus carrying cfr(B). E. raffinosus carrying cfr(B) without linezolid resistance poses a threat, as it could serve as a reservoir for mobile linezolid resistance genes.