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