Background: With 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.
Methods: The minimum inhibitory concentration (MIC) levels was determined by the agar dilution method, and polymerase chain reaction (PCR) 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 lentus H29, was characterized, and comparative genomics analysis of the resistance gene-related sequences was also performed.
Results: As a result, the isolates from the animals showed a higher resistance rate (23/28, 82.1%) and much higher MIC levels of florfenicol than those from seafood. Twenty-seven animal isolates carried 37 florfenicol resistance genes (including 26 fexA , 6 cfr and 5 fexB genes), of which 1 carried a cfr gene, 16 carried a fexA gene, 5 carried both fexA and fexB genes and 5 carried both fexA and cfr genes. On the other hand, all 11 isolates from seafood were sensitive to florfenicol, and only 3 carried a fexA gene each. The whole genome sequence of S. lentus H29 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 , aac A -aph D , mecA and mph(C) ] encoded on the chromosome, four genes [ cfr, fexA, aac A -aph D and tcaA ] on pH29-46 and one gene ( fosD ) on pH29-26. It was interested to find that the S. lentus H29 genome carried two identical copies of the gene arrays of radC - tnpABC - hp - fexA (5,671 bp) and IS 256 - cfr (2,690 bp), of which one copy of the two gene arrays was encoded on plasmid pH29-46, while the other was encoded on the chromosome.
Conclusions : The current study revealed the wide distribution of florfenicol resistance genes ( cfr, fexA and fexB ) in animal bacteria, and to the best of our knowledge, this is the first report of one CoNS strain carrying two identical copies of florfenicol resistance-related gene arrays.