AUTHOR=Zou Jiaqi , Tang Zhaobing , Yan Jia , Liu Hang , Chen Yingzhu , Zhang Dawei , Zhao Jinxin , Tang Yu , Zhang Jing , Xia Yun 

TITLE=Dissemination of Linezolid Resistance Through Sex Pheromone Plasmid Transfer in Enterococcus faecalis

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01185

DOI=10.3389/fmicb.2020.01185

ISSN=1664-302X

ABSTRACT=<p>Despite recent recognition of the ATP-binding cassette protein OptrA as an important mediator of linezolid resistance in <italic>Enterococcus faecalis</italic> worldwide, the mechanisms of <italic>optrA</italic> gene acquisition and transfer remain poorly understood. In this study, we performed comprehensive molecular and phenotypic profiling of 44 <italic>optrA</italic>-carrying <italic>E. faecalis</italic> clinical isolates with linezolid resistance. Pulse-field gel electrophoresis and DNA hybridization revealed the presence of <italic>optrA</italic> in the plasmid in 26 (59%) isolates and in the chromosome in 18 (41%) isolates. Conjugation experiments showed a successful transfer of <italic>optrA</italic> in 88.5% (23/26) of isolates carrying <italic>optrA</italic> in plasmids while no transfer occurred in any isolates carrying <italic>optrA</italic> in the chromosome (0/18). All 23 transconjugants exhibited <italic>in vitro</italic> resistance to linezolid and several other antibiotics and were confirmed to contain <italic>optrA</italic> and other resistance genes. Plasmid typing demonstrated a predominance (18/23,78%) of <italic>rep</italic><sub>9</sub>–type plasmids (pCF10 prototype) known to be the best studied sex pheromone responsive plasmids. Full plasmid genome sequencing of one isolate revealed the presence of drug resistance genes (<italic>optrA</italic> and <italic>fexA</italic>) and multiple sex pheromone response genes in the same plasmid, which represents the first sex pheromone responsive plasmid carrying <italic>optrA</italic> from a clinical isolate. PCR-based genotyping revealed the presence of three key sex pheromone response genes (<italic>prgA, prgB</italic>, and <italic>prgC</italic>) in 23 <italic>optrA</italic>-carrying isolates. Finally, functional studies of these isolates by clumping induction assay detected different degrees of clumping in 17 isolates. Our analysis suggests that <italic>optrA</italic>-mediated linezolid resistance can be widely disseminated through sex pheromone plasmid transfer.</p>