Co-existence of the oxazolidinone resistance genes cfr and optrA on two transferable multiresistance plasmids in one Enterococcus faecalis isolate from swine

ABSTRACT Objectives This study aimed at identifying and characterizing oxazolidinone resistance genes cfr and optrA in Enterococcus isolates. Methods We screened 293 Enterococcus isolates for the presence of cfr and optrA genes by PCR. The transferability of cfr and optrA was examined by conjugation. S1 nuclease PFGE and Southern blotting were used to identify the location of cfr and optrA. One Enterococcus faecalis isolate carrying both cfr and optrA genes was completely sequenced. Results The cfr and optrA genes were detected in 16 (5.5%) and 170 (58.0%) Enterococcus isolates, respectively. Sixteen Enterococcus isolates (E. faecalis n=13; Enterococcus avium n=2; Enterococcus mundtii n=1) carried both cfr and optrA genes. The cfr-carrying fragment between res and theta in plasmid p4 showed 98.9% identity to the corresponding region of plasmid pEF120805 from vancomycin-resistant Enterococcus faecium. The optrA-carrying segment between tnpB and optrA in plasmid p1 showed >99.9% identity to the corresponding region of genomic DNA from E. faecalis A101. Plasmid p4 and plasmid p1 were simultaneously conjugated to E. faecalis JH2-2. Conclusions It was worth noting that 170 optrA-positive enterococci were identified in 293 Enterococcus isolates from swine and farm environment. The co-existence of cfr and optrA genes in E. avium and E. mundtii was first identified. The cfr and optrA genes were identified on two new conjugative plasmids from one E. faecalis isolate. The optrA-carrying segment (IS1216E-optrA-IS1216E) was first reported. Among different types of enterococcal plasmids, ISEnfa5 and IS1216E elements may play a vital role in the dissemination of cfr and optrA, respectively.