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

• Main Authors: Simona Fioriti, Gianluca Morroni, Sonia Nina Coccitto, Andrea Brenciani, Alberto Antonelli, Vincenzo Di Pilato, Ilaria Baccani, Simona Pollini, Lucilla Cucco, Alessandra Morelli, Marta Paniccià, Chiara Francesca Magistrali, Gian Maria Rossolini, Eleonora Giovanetti
• Format: Article
• Language: English
• Published: MDPI AG 2020-12-01
• Series: Microorganisms
• Subjects: <i>Enterococcus faecium</i>; <i>Enterococcus faecalis</i>; <i>Enterococcus</i> spp.; oxazolidinone resistance; <i>cfr</i>; <i>cfr</i>(D)
• Online Access: https://www.mdpi.com/2076-2607/8/12/2021

One hundred forty-five florfenicol-resistant enterococci, isolated from swine fecal samples collected from 76 pig farms, were investigated for the presence of <i>optrA</i>, <i>cfr</i>, and <i>poxtA</i> genes by PCR. Thirty florfenicol-resistant <i>Enterococcus</i> isolates had at least one linezolid resistance gene. <i>optrA</i> was found to be the most widespread linezolid resistance gene (23/30), while <i>cfr</i> and <i>poxtA</i> were detected in 6/30 and 7/30 enterococcal isolates, respectively. WGS analysis also showed the presence of the <i>cfr</i>(D) gene in <i>Enterococcus faecalis</i> (<i>n</i> = 2 isolates) and in <i>Enterococcus avium</i> (<i>n</i> = 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 <i>optrA</i> genetic contexts identical or related to transposons (Tn<i>6628</i> and Tn<i>6674</i>), plasmids (pE035 and pWo27-9), and chromosomal regions. <i>cfr</i> environments showed identities with Tn<i>6644</i>-like transposon and a region from p12-2300 plasmid; <i>cfr</i>(D) genetic contexts were related to the corresponding region of the plasmid 4 of <i>Enterococcus faecium</i> E8014; <i>poxtA</i> was always found on Tn<i>6657</i>. Circular forms were obtained only for <i>optrA</i>- and <i>poxtA</i>-carrying genetic contexts. Clonality analysis revealed the presence of <i>E. faecalis</i> (ST16, ST27, ST476, and ST585) and <i>E. faecium</i> (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.