Transferable Resistance Gene <i>optrA</i> in Enterococcus faecalis from Swine in Brazil

Abstract

OptrA is an ATP-binding cassette (ABC)-F protein that confers resistance to oxazolidinones and phenicols and can be either plasmid-encoded or chromosomally encoded. Here, we isolated 13 <i>Enterococcus faecalis</i> strains possessing a linezolid MIC of ≥4 mg/liter from nursery pigs in swine herds located across Brazil. Genome sequence comparison showed that these strains possess <i>optrA</i> in different genetic contexts occurring in 5 different <i>E. faecalis</i> sequence type backgrounds. The <i>optrA</i> gene invariably occurred in association with an <i>araC</i> regulator and a gene encoding a hypothetical protein. In some contexts, this genetic island was able to excise and form a covalently closed circle within the cell; this circle appeared to occur in high abundance and to be transmissible by coresident plasmids.