Rapid emergence of highly variable and transferable oxazolidinone and phenicol resistance gene optrA in German Enterococcus spp. clinical isolates.
Int J Antimicrob Agents. 2018 Sep 17;:
Authors: Bender JK, Fleige C, Lange D, Klare I, Werner G
Ever since 2011, the National Reference Centre for Staphylococci and Enterococci in Germany receives an increasing number of linezolid-resistant Enterococcus (E.) spp. isolates. Although the majority belongs to the species E. faecium, clinical linezolid-resistant E. faecalis were isolated too. With respect to the newly discovered linezolid resistance protein OptrA, we herein conducted a retrospective PCR-screening of 698 linezolid-resistant Enterococcus clinical isolates. That yielded 43 optrA-positive strains of which a subset was analyzed by whole genome sequencing in order to infer linezolid resistance-associated mechanisms, phylogenetic relatedness and to disclose optrA genetic environments. Multiple optrA variants were detected. The originally described variant from China, optrAWT, was the only one shared between the two Enterococcus species; however, distinct optrAWT loci were detected for E. faecium and E. faecalis. Generally, optrA localized to a plethora of genetic backgrounds that differed even for identical optrA variants. This suggests transmission of a mobile genetic element harboring the resistance locus. Additionally, identical optrA variants detected on presumably identical plasmids, that were present in unrelated strains, indicates dissemination of the entire optrA-containing plasmid. In accordance, in vitro conjugation experiments verified transfer of optrA plasmids between enterococci of the same and of different species. In conclusion, multiple optrA variants located on distinct plasmids and mobile genetic elements with the potential of conjugative transfer are supposedly causative for the emergence of optrA-positive enterococci. Hence, rapid dissemination of the resistance determinant under selective pressure imposed by extensive use of last resort antibiotics in clinical settings could be expected.
PMID: 30236952 [PubMed - as supplied by publisher]