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

Bacterial resistance to the antibiotics has become an important concern for public health. This study was aimed to investigate the characteristics and distribution of the florfenicol-related resistance genes in bacteria isolated from 4 farms. A total of 106 florfenicol-resistant Gram-negative bacilli were examined for florfenicol-related resistance genes and the positive isolates were further characterized. Antimicrobial sensitivity results showed that most of them (100, 94.33%) belonged to multidrug resistance Enterobacteriaceae. About 91.51% of the strains carried floR gene, 4.72% carried cfr gene. According to the Pulsed-field gel electrophoresis (PFGE) results, 34 E. coli were subdivided into 22 profiles, the Genetic Similarity coefficient ranged from 80.3% to 98.0%. Multilocus sequence typing (MLST) results revealed 17 sequence types (STs), with ST10 being the most prevalent. The genome sequencing result showed that Proteus vulgaris 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 floR located in a drug resistant region on the chromosome of P. vulgaris G32 was with IS91 family transposase, and the other floR gene on the plasmid pG32-177 was with an ISCR2 insertion sequence. The cfr gene was located on the pG32-51 flanked by IS26 element and TnpA26. This study suggested that the mobile genetic elements played an important role in the resistance genes replication and the horizontal resistance gene transfer.