Analysis of Resistance to Florfenicol and the Related Mechanism of Dissemination in Different Animal-Derived Bacteria

Abstract

Bacterial resistance to antibiotics has become an important concern for public health. This study was aimed to investigate the characteristics and the distribution of the florfenicol-related resistance genes in bacteria isolated from four farms. A total of 106 florfenicol-resistant Gram-negative bacilli were examined for florfenicol-related resistance genes, and the positive isolates were further characterized. The antimicrobial sensitivity results showed that most of them (100, 94.33%) belonged to multidrug resistance <i>Enterobacteriaceae</i>. About 91.51% of the strains carried <i>floR</i> gene, while 4.72% carried <i>cfr</i> gene. According to the pulsed-field gel electrophoresis results, 34 <i>Escherichia coli</i> were subdivided into 22 profiles, the genetic similarity coefficient of which ranged from 80.3 to 98.0%. The multilocus sequence typing (MLST) results revealed 17 sequence types (STs), with ST10 being the most prevalent. The genome sequencing result showed that the <i>Proteus vulgaris</i> G32 genome consists of a 4.06-Mb chromosome, a 177,911-bp plasmid (pG32-177), and a 51,686-bp plasmid (pG32-51). A <i>floR</i> located in a drug-resistant region on the chromosome of <i>P. vulgaris</i> G32 was with IS<i>91</i> family transposase, and the other <i>floR</i> gene on the plasmid pG32-177 was with an IS<i>CR2</i> insertion sequence. The <i>cfr</i> gene was located on the pG32-51 flanked by IS<i>26</i> element and TnpA26. This study suggested that the mobile genetic elements played an important role in the replication of resistance genes and the horizontal resistance gene transfer.