Molecular Epidemiology and Horizontal Transfer Mechanism of <i>optrA</i> -Carrying Linezolid-Resistant <i>Enterococcus faecalis</i>

The aim of this work was to provide a theoretical and scientific basis for the treatment, prevention, and control of clinical drug-resistant bacterial infections by studying the molecular epidemiology and horizontal transfer mechanism of <i>optrA</i>-carrying linezolid-resistant <i>Enterococcus faecalis</i> strains (LREfs) that were clinically isolated in a tertiary hospital in Kunming, China. Non-repetitive LREfs retained in a tertiary A hospital in Kunming, China. The strains were identified by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The transferability and horizontal transfer mechanism of <i>optrA</i> gene were analyzed using polymerase chain reaction (PCR), whole-genome sequencing (WGS), and conjugation experiments. A total of 39 LREfs strains were collected, and all of them were multi-drug resistant. There were 30 LREfs strains (76.9%) carrying the <i>optrA</i> gene, The <i>cfr, poxtA</i> genes and mutations in the 23S rRNA gene were not detected. The conjugation experiments showed that only three of 10 randomly selected <i>optrA</i>-carrying LREfs were successfully conjugated with JH2-2. Further analysis of one successfully conjugated strain revealed that the <i>optrA</i> gene, located in the donor bacterium, formed the <i>IS1216E-erm(A)-optrA-fexA-IS1216E</i> transferable fragment under the mediation of the mobile genetic element (MGE) <i>IS1216E</i>, which was then transferred to the recipient bacterium via horizontal plasmid transfer. Carrying the <i>optrA</i> gene is the primary resistance mechanism of LREfs strains. The <i>optrA</i> gene could carry the <i>erm(A)</i> and <i>fexA</i> genes to co-transfer among <i>E. faecalis</i>. MGEs such as insertion sequence <i>IS1216E</i> play an important role in the horizontal transfer of the <i>optrA</i> gene.