Characterization of florfenicol resistance genes in the coagulase-negative Staphylococcus (CoNS) isolates and genomic features of a multidrug-resistant Staphylococcus lentus strain H29

BackgroundWith the wide use of florfenicol to prevent and treat the bacterial infection of domestic animals, the emergence of the florfenicol resistance bacteria is increasingly serious. It is very important to elucidate the molecular mechanism of the bacteria’s resistance to florfenicol.MethodsThe minimum inhibitory concentration (MIC) levels were determined by the agar dilution method, and polymerase chain reaction was conducted to analyze the distribution of florfenicol resistance genes in 39 CoNS strains isolated from poultry and livestock animals and seafood. The whole genome sequence of one multidrug resistant strain,Staphylococcus lentusH29, was characterized, and comparative genomics analysis of the resistance gene-related sequences was also performed.ResultsAs a result, the isolates from the animals showed a higher resistance rate (23/28, 82.1%) and much higher MIC levels to florfenicol than those from seafood. Twenty-seven animal isolates carried 37 florfenicol resistance genes (including 26fexA, 6cfrand 5fexBgenes) with one carrying acfrgene, 16 each harboring afexAgene, 5 with both afexAgene and afexBgene and the other 5 with both afexAgene and acfrgene. On the other hand, all 11 isolates from seafood were sensitive to florfenicol, and only 3 carried afexAgene each. The whole genome sequence ofS. lentusH29 was composed of a chromosome and two plasmids (pH29-46, pH29-26) and harbored 11 resistance genes, including 6 genes [cfr, fexA, ant(6)-Ia,aacA-aphD, mecAandmph(C)] encoded on the chromosome, 4 genes [cfr, fexA, aacA-aphDandtcaA] on pH29-46 and 1 gene (fosD) on pH29-26. We found that theS. lentusH29 genome carried two identical copies of the gene arrays ofradC-tnpABC-hp-fexA(5671 bp) and IS256-cfr(2690 bp), of which one copy of the two gene arrays was encoded on plasmid pH29-46, while the other was encoded on the chromosome.ConclusionsThe current study revealed the wide distribution of florfenicol resistance genes (cfr, fexAandfexB) in animal bacteria, and to the best of our knowledge, this is the first report that oneS. lentusstrain carried two identical copies of florfenicol resistance-related gene arrays.