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

Simona Fioriti,Andrea Brenciani,Ilaria Baccani,Chiara Francesca Magistrali,Lucilla Cucco,Alessandra Morelli,Eleonora Giovanetti,Gianluca Morroni,Marta Paniccià,Simona Pollini,Vincenzo Di Pilato,Sonia Nina Coccitto,Alberto Antonelli,Gian Maria Rossolini

doi:10.3390/microorganisms8122021

Abstract

One hundred forty-five florfenicol-resistant enterococci, isolated from swine fecal samples collected from 76 pig farms, were investigated for the presence of optrA, cfr, and poxtA genes by PCR. Thirty florfenicol-resistant Enterococcus isolates had at least one linezolid resistance gene. optrA was found to be the most widespread linezolid resistance gene (23/30), while cfr and poxtA were detected in 6/30 and 7/30 enterococcal isolates, respectively. WGS analysis also showed the presence of the cfr(D) gene in Enterococcus faecalis (n = 2 isolates) and in Enterococcus avium (n = 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 optrA genetic contexts identical or related to transposons (Tn6628 and Tn6674), plasmids (pE035 and pWo27-9), and chromosomal regions. cfr environments showed identities with Tn6644-like transposon and a region from p12-2300 plasmid; cfr(D) genetic contexts were related to the corresponding region of the plasmid 4 of Enterococcus faecium E8014; poxtA was always found on Tn6657. Circular forms were obtained only for optrA- and poxtA-carrying genetic contexts. Clonality analysis revealed the presence of E. faecalis (ST16, ST27, ST476, and ST585) and E. faecium (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.

Highlights

Oxazolidinones, including linezolid and tedizolid, are antibiotics approved for clinical use to treat serious infections by Gram-positive pathogens, including MRSA, VRE, multidrug-resistant (MDR) pneumococci, and MDR mycobacteria
The analysis of the deduced OptrA sequences revealed that four isolates harbored the wild-type OptrAE349, identical to that from E. faecalis E349 [10], while nineteen carried eight OptrA variants, five of which were original (Table 2)
Oxazolidinones are not approved for veterinary use, linezolid resistance genes have been detected in animal and environmental bacteria worldwide, likely due to their co-selection by different agents that are affected by the encoded resistance determinants (e.g., OptrA, Cfr, and PoxtA proteins)

Summary

Introduction

Oxazolidinones, including linezolid and tedizolid, are antibiotics approved for clinical use to treat serious infections by Gram-positive pathogens, including MRSA, VRE, multidrug-resistant (MDR) pneumococci, and MDR mycobacteria. Transferable resistance mechanisms to oxazolidinones have emerged during the past decade. These mechanisms include: (i) post-transcriptional methylation of the 23S rRNA by the Cfr (chloramphenicol and florfenicol resistance) and Cfr-like methylases, which confer resistance to five classes of antimicrobial agents including phenicols, lincosamides, oxazolidinones, pleuromutilines and streptogramin A (PhLOPSA phenotype) [5,6,7,8,9]; (ii) ribosomal protection by the ABC-F proteins OptrA (oxazolidinone phenicol transferable resistance) and PoxtA (phenicols, oxazolidinones and tetracyclines) leading to a decreased susceptibility to phenicols, oxazolidinones (including tedizolid), and tetracyclines (PoxtA only) [10,11,12]

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Conclusion