Detection of Oxazolidinone Resistance Genes and Characterization of Genetic Environments in Enterococci of Swine Origin, Italy.

One hundred forty-five florfenicol-resistant enterococci, isolated from swine fecal samples collected from 76 pig farms, were investigated for the presence of , , and genes by PCR. Thirty florfenicol-resistant isolates had at least one linezolid resistance gene. was found to be the most widespread linezolid resistance gene (23/30), while and were detected in 6/30 and 7/30 enterococcal isolates, respectively. WGS analysis also showed the presence of the (D) gene in ( = 2 isolates) and in ( = 1 isolate). The linezolid resistance genes hybridized both on chromosome and plasmids ranging from ~25 to ~240 kb. Twelve isolates were able to transfer linezolid resistance genes to enterococci recipient. WGS analysis displayed a great variability of genetic contexts identical or related to transposons (Tn and Tn), plasmids (pE035 and pWo27-9), and chromosomal regions. environments showed identities with Tn-like transposon and a region from p12-2300 plasmid; (D) genetic contexts were related to the corresponding region of the plasmid 4 of E8014; was always found on Tn. Circular forms were obtained only for - and -carrying genetic contexts. Clonality analysis revealed the presence of (ST16, ST27, ST476, and ST585) and (ST21) clones previously isolated from humans. These results demonstrate a dissemination of linezolid resistance genes in enterococci of swine origin in Central Italy and confirm the spread of linezolid resistance in animal settings.