Oxazolidinone Resistance Mediated Byoptrain Clinicalenterococcus Faecalisisolates In Upper Austria: First Report And Characterization By Whole Genome Sequencing

The genetic mechanisms associated with acquisition of linezolid (LZD) resistance are diverse, including point mutations in the V domain of the 23S rRNA and the 50S ribosomal proteins as well ascfr,optrA, and/orpoxtA genes, which may be plasmid- or chromosomally encoded. The aim of this study was to investigate through Whole Genome Sequencing (WGS)-based typing the presence and location of genes and point mutations associated with LZD resistance in twoEnterococcus faecalisisolates from Upper Austrian patients. The isolates were retrieved during screening by LZD disk diffusion test of a total of 911 clinicalE. faecalisisolates in 2017. The twoE. faecalisisolates had LZD minimum inhibitory concentrations of 8 and 32 mg/L and wereoptrA-positive (ST476 and ST585). Bioinformatic analysis revealed the presence ofoptrA located in the chromosome of both isolates. One isolate carried theoptrA gene in the transposon 6674, previously reported as chromosomally encoded, and the second isolate in fragments originating from the integrative plasmid pEF10748. Additional mechanisms of LZD resistance on the 23S rRNA and the 50S ribosomal proteins were detected. None of the patients reported travels to geographical areas with high LZD resistance or previous LZD treatments. This is the first report ofoptrAcarryingE. faecalis, including characterization by WGS from Austria. LZD resistance in a low-prevalence setting is of concern and should be further monitored.