Characterization of a novel RepA_N-family plasmid harbouring the phenicol-oxazolidinone resistance gene optrA in Enterococcus faecalis ST16 high-risk clone of goat origin.

The occurrence and dissemination of linezolid-resistant Gram-positive bacteria among food-producing animals poses severe threats to public health. To date, information about the emergence of the oxazolidinone resistance gene optrA in isolates from goats is scare. In this study, the optrA-positive multiresistant E. faecalis strain SY-1 was isolated from a goat in China. E. faecalis strain SY-1 displayed a multidrug resistance profile for most of antimicrobial agents tested, including linezolid and tedizolid. MLST analysis showed that E. faecalis strain SY-1 belonged to the high-risk clone ST16. Whole genome sequencing analysis revealed that the optrA gene together with several other resistance genes was located on a novel RepA_N-family plasmid pSY-1-optrA. Detailed sequence analysis indicated that pSY-1-optrA exhibited a mosaic structure that may be the result of recombination events. In addition, a mobile bacitracin resistance operon bcrABDR was identified on plasmid pSY-1-optrA. In conclusion, this is, to our knowledge, the first report of the optrA gene in the high-risk clone E. faecalis ST16 of goat origin. Active surveillance of optrA-positive E. faecalis high-risk clones in food-producing animals is urgently warranted.