Commentary: Nationwide Surveillance of Novel Oxazolidinone Resistance Gene optrA in Enterococcus Isolates in China from 2004 to 2014

A distictive feature of the novel oxazolidinone-phenicol resistance gene optrA is a variability yielding an encoded OptrA protein-a 655 amino acid sequence-which is variable in turn. The issue of the OptrA variants was more regularly addressed in the early studies of the new resistance than in the following reports. It is thus with particular interest that we read the recent nationwide surveillance study by Cui et al. (2016), where a wide screening of Chinese enterococci for optrA gave the authors an opportunity to repropose the issue of the different variants of the optrA protein. When optrA was first reported in China from a 1998 to 2014 collection of human and animal enterococci (incidence, 2.0 and 15.9%, respectively), the optrA-carrying plasmid from a human Enterococcus faecalis isolate (E349) was sequenced (accession no. KP399637) (Wang et al., 2015). The relevant optrA-encoded protein is regarded as the wild type, and is hereinafter referred to as OptrAE349. Soon after the discovery of optrA, over a thousand enterococci, randomly collected in 2010-2014, were screened for the gene: among the optrA-positive isolates (incidence, 2.9%), nine different variants of theOptrA sequence (one being identical to OptrAE349) were detected (Cai et al., 2015). Seventeen optrA-positive, unrelated isolates of E. faecalis from the aforementioned 19982014 collection disclosed optrA sequences consistent with no new OptrA variant (seven isolates had OptrAE349) (He et al., 2016). Finally-in China, yet again-while screening over two thousand enterococci collected in 2004-2014, Cui et al. (2016) detected among the optrA-positive isolates (incidence, 2.0%) three new OptrA variants. Thus, the different OptrA sequences so far described in Chinese enterococci total 12 (including OptrAE349). Meanwhile, as soon as the optrA sequence became available, we detected in Italy the gene-first report of optrA outside China-in two clinically distinct but virtually identical Enterococcus faecium isolates from a collection of 81 blood enterococci (incidence, 2.5%) recovered in 2015 (Brenciani et al., 2016). One of the two E. faeciumisolates (strain E35048) was investigated for molecular traits, and its optrA gene (accession no. KT892063) displayed 98% DNA identity to the wild type gene.