Molecular Epidemiology and Horizontal Transfer Mechanism of optrA-Carrying Linezolid-Resistant Enterococcus faecalis

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 optrA-carrying linezolid-resistant Enterococcus faecalis 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 optrA 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 optrA gene, The cfr, poxtA genes and mutations in the 23S rRNA gene were not detected. The conjugation experiments showed that only three of 10 randomly selected optrA-carrying LREfs were successfully conjugated with JH2-2. Further analysis of one successfully conjugated strain revealed that the optrA gene, located in the donor bacterium, formed the IS1216E-erm(A)-optrA-fexA-IS1216E transferable fragment under the mediation of the mobile genetic element (MGE) IS1216E, which was then transferred to the recipient bacterium via horizontal plasmid transfer. Carrying the optrA gene is the primary resistance mechanism of LREfs strains. The optrA gene could carry the erm(A) and fexA genes to co-transfer among E. faecalis. MGEs such as insertion sequence IS1216E play an important role in the horizontal transfer of the optrA gene.