Linezolid-Resistant Enterococcus faecalis of Chicken Origin Harbored Chromosome-Borne optrA and Plasmid-Borne cfr , cfr (D), and poxtA2 Genes.

The aim of this study was to investigate the transferability of acquired linezolid resistance genes and associated mobile genetic elements in an Enterococcus faecalis isolate QZ076, cocarrying , , (D), and genes. MICs were determined by broth microdilution. Whole-genome sequencing (WGS) was performed using the Illumina and Nanopore platforms. The transfer of linezolid resistance genes was investigated by conjugation, using E. faecalis JH2-2 and clinical methicillin-resistant Staphylococcus aureus (MRSA) 109 as recipients. E. faecalis QZ076 harbors four plasmids, designated pQZ076-1 to pQZ076-4, with located in the chromosomal DNA. The gene was located on a novel pseudocompound transposon, designated Tn, integrated into the 65,961-bp pCF10-like pheromone-responsive conjugative plasmid pQZ076-1. Tn generated 8-bp direct target duplications (5'-GATACGTA-3'). The genes (D) and were colocated on the 16,397-bp mobilizable broad-host-range Inc18 plasmid pQZ076-4. The -carrying plasmid pQZ076-1 could transfer from E. faecalis QZ076 to E. faecalis JH2-2, along with the (D)- and -cocarrying plasmid pQZ076-4, conferring the corresponding resistant phenotype to the recipient. Moreover, pQZ076-4 could also transfer to MRSA 109. To the best of our knowledge, this study presented the first report of four acquired linezolid resistance genes [, , (D), and ] being simultaneously present in the same E. faecalis isolate. The location of the gene on a pseudocompound transposon in a pheromone-responsive conjugative plasmid will accelerate its rapid dissemination. In addition, the -carrying pheromone-responsive conjugative plasmid in E. faecalis was also able to mobilize the interspecies transfer of the (D)- and -cocarrying plasmid between enterococci and staphylococci. In this study, the simultaneous occurrence of four acquired oxazolidinone resistance genes [, , (D), and ] was identified in an E. faecalis isolate of chicken origin. The association of the gene with a novel pseudocompound transposon Tn integrated into a pCF10-like pheromone-responsive conjugative plasmid will accelerate its dissemination. Moreover, the location of the resistance genes (D) and on a mobilizable broad-host-range Inc18 family plasmid represents the basis for their intra- and interspecies dissemination with the aid of a conjugative plasmid and further accelerates the spreading of acquired oxazolidinone resistance genes, such as , (D), and , among Gram-positive pathogens.