The Epidemiological Study On The Oxazolidinones Resistance Genescfr And OptrA And Theirs Transmission Mechanism Among MRSA And CoNS Isolates From Swine

Methicillin-resistant Stahylococcus aureus (MRSA) and methicillin-resistant congulase negativestaphylococci(MRCoNS) are the important pathogens causing community-and nosocomial infections. The mentionable microbiology could be detected from health animals, veterinary and slaughter staff who contacts with animals. The resistance gene among MRSA and MRCoNS could be transmitted to human via food chain, which may be threatedhuman health.Linezolid is the few clinical effective drugs to treat infection by MRSA and MRCoNS. The transferable resistance gene cfr, located on plasmid had been reported among human and animals among various Staphylococci andEnterococci. Tedizolid could be effective drug to treatment infection by MRSAand MRCoNS including the cfr positive strain, but a novel transferable gene optrAwas resistant or reduced the susceptibility to phenicols and oxazolidones.Up to now, no researchers focused on the epidemiological characterization and mechanism of transmission of cfr and optrA among MRSA from swine and optrA in MRCoNS. So, we investigated the epidemiology of cfr and optrA in MRSA and CoNS, transmission mechanism, and genetic environment of genes cfr and optrA.This study project will provide scientific basis for both risk assessment and the prevalence two Oxazolidinones resistance gene。From 2013 to 2014, a total of MRSA (n=400), MRCoNS (n=525) and FRCoNS (n=594) were isolated.The rate of cfr in MRSA and optrA in MRCoNS and FRCoNS were 2.8%(n=11),6.5%(n=34) and 3.4%(n=20), respectively. Moreover, the rate of cfr gene among optrA positive MRCoNS and FRCoNS were 17.6% and 55.0%, respectively.Thecfr gene in MRSA was detected on plasmids of ca.35 kb in 10isolates, and one located into Chromosome. Most cfr gene may be mediated by IS21-558. For the first time, an ISEnfa4-cfr-1S256 fragment was found to be inserted upstream of the ccr genes in a chromosomal SCCmec IVb element of the remaining isolate.One optrA positive MRCoNS(Staphylococcus sciuri) strain wo28-3 was firstly detected from Guangdong province. Functionality of this gene was confirmed by cloning and expression in a susceptible Stahylococcus host.This optrA variant also conferred resistance to oxazolidinones and phenicols in staphylococci. The location of the genes optrA and cfr were analysed by S1-PFGE and Southern blot analysis.Thecp/r A-carrying plasmidwas completely sequenced and analysed, which harboured the resistance genes cfr,fexA, aadD, ble and aacA-aphDand highly identical to pJP1-like.Then location of optrA and cfr among MRCoNs in 2014 was conducted by S1-PFGE and Southern blot. Among the 33 optrA positive strains, the four optrA and cfr co-existed located on plasmidstrains carried the pWo28-3-like plasmid, and they had the same resistance genes cluster.Six differences genetic background were obtained in the rest optrA positive strains, which located into Chromosome. All the genes located into Chromosome had the basic structure:transcriptional regulator gene araC and optrA. Some strains had a complete Tn558 adjacent with the araC, which was different in the direct or indirect with the joining region between optrA-arac andTn558.There were three strains carrying optrA which were adjacent with the ccr complex.Twenty FRCoNS isolates were conducted by S1-PFGE southern blot and whole genomic DNA and /or whole plasmid DNA sequenced. Interesting, gene cfr and optrA co-existed in 11 strains.Two cfr and optrA co-existed and located on plasmid, which had the same gentic determinats with pWo28-3 like.8 cfr strains shared the same genetic determinats with pJP1-like.There were four cfr and optrA co-existed strains located into chromosome and the upstream of optrA were ISenfa5 and cfr.in three strains.In addition, There was three others genetic background in only optrA positive strain.In all, for the first time, an ISEnfa4-cfr-IS256 fragment was found to be inserted into the upstream of the ccr genes in a chromosomal SCCmec IVb element in MRSA strain. To our knowledge, this is the first report of the prevalence of optrA gene in CoNSand of the coexistence of optrA and cfr on the same plasmid in MRCoNS.Meanwhile, a system study of optrA and cfr in CoNS was conducted. Dissemination of these genes will substantially limit the efficacy of oxazolidinones. Surveillance of optrAand cfr in staphylococci of both human and animal origin is urgently warranted.