Detection of transferable oxazolidinone resistance determinants in Enterococcus faecalis and Enterococcus faecium of swine origin in Sichuan Province, China

Abstract Objectives The aim of this study was to detect the transferable oxazolidinone resistance determinants ( cfr , optrA and poxtA ) in E. faecalis and E. faecium of swine origin in Sichuan Province, China. Methods A total of 158 enterococci strains (93 E. faecalis and 65 E. faecium ) isolated from 25 large-scale swine farms were screened for the presence of cfr , optrA and poxtA by PCR. The genetic environments of cfr , optrA and poxtA were characterized by whole genome sequencing. Transfer of oxazolidinone resistance determinants was determined by conjugation or electrotransformation experiments. Results The transferable oxazolidinone resistance determinants, cfr , optrA and poxtA , were detected in zero, six, and one enterococci strains, respectively. The poxtA in one E. faecalis strain was located on a 37,990 bp plasmid, which co-harbored fexB , cat , tet (L) and tet (M), and could be conjugated to E. faecalis JH2-2. One E. faecalis strain harbored two different OptrA variants, including one variant with a single substitution, Q219H, which has not been reported previously. Two optrA -carrying plasmids, pC25-1, with a size of 45,581 bp, and pC54, with a size of 64,500 bp, shared a 40,494 bp identical region that contained genetic context IS 1216E - fexA - optrA - erm (A)-IS 1216E , which could be electrotransformed into Staphylococcus aureus . Four different chromosomal optrA gene clusters were found in five strains, in which optrA was associated with Tn 554 or Tn 558 that were inserted into the radC gene. Conclusion Our study highlights the fact that mobile genetic elements, such as plasmids, IS 1216E , Tn5 54 and Tn 558 , may facilitate the horizontal transmission of optrA or poxtA .