Complete genome sequence of optrA-carrying Enterococcus faecalis isolated from open pus in a Japanese patient

Objectives: The occurrence of linezolid resistance in enterococci has recently increased. Here, we report the genomic characterization of Enterococcus faecalis strain JARB-HU0796-isolated from the open pus of a patient in Hiroshima, Japan-which shows nonsusceptibility to linezolid (MIC of 4 µg/mL).

Methods: JARB-HU0796 whole-genome sequencing was performed using short-read sequencing with Illumina Hiseq X Five and long-read sequencing using GridION. These reads were collected using the assembly pipeline Unicycler and annotated with DFAST. Antimicrobial resistance genes were detected using the Abricate and ResFinder databases, and the sequence type identified using PubMLST. The antimicrobial susceptibility of JARB-HU0796 was determined with the Eiken dry-plate QH02 system.

Results: The JARB-HU0796 complete genome contained a circular chromosome (2 722 585 bp) and two circular plasmids (85 996 bp and 58 872 bp). The chromosome harbours the optrA gene, which confers resistance to oxazolidinones and phenicols. JARB-HU0796 showed nonsusceptibility to linezolid and multidrug resistance to other antibiotics. MLST analysis identified JARB-HU0796 as ST476, similar to the optrA-positive E. faecalis ST476 isolates from swine (South Korea, 2020) and pet food (Switzerland, 2022). The optrA region of JARB-HU0796 is nearly identical to that of ST476 E. faecalis strain TZ2, isolated from humans (China, 2013).

Conclusions: To the best of our knowledge, this is the first report of the complete genome sequence of E. faecalis ST476 carrying optrA on a chromosome isolated from a patient in Japan. The strain may have originated in animals, suggesting that the organisms acquired resistance to linezolid because the optrA gene may be closely spread between animals and humans.