Investigation On The Resistance Situation In Enterococci Strains From Various Resources And Its Resistance Mechanism To Florfenicol

Multidrug resistance characteristics of Enterococcus, as well as the emergence of vancomycin-resistant enterococci, has caused widespread concern in the medical and veterinary clinic. Florfenicol, a broad-spectrum antibiotic only approved for use in animals, has the higher antibacterial activity and lower toxic side effects, which is mainly used for the prevention and control of bacterial diseases in food-producing animals such as cattle, pigs, chickens and fish. Therefore, the study on the resistance mechanism of enterococci to florfenicol has important public health significance to food safety and human health.In this study, 149 Enterococci strains were isolated and identified from different sources(humans, pigs, fresh meat and food). Then, the antimicrobial susceptibility testing, detection of florfenicol resistance gene(cfr, fex A, fex B), plasmid conjugation and transformation experiments, genetic environmental analysis of the resistance genes were performed to investigate the resistance mechanism of Enterococci to florfenicol. In addtion, the detection of the pathogenicity island marker gene esp, MLST typing were done to explore the possibility of transmission among Enterococcus faecalis of the different sources.The results showed that 72 Enterococcus faecalis and 40 Enterococcus faecium were isolated and identified. The resistance rates of 149 enterococci strains to vancomycin, teicoplanin, chloramphenicol, gentamicin, ciprofloxacin, tetracycline, erythromycin, ampicillin, quinupristin/dalfopristin and florfenicol were 57%, 10%, 44%, 94%, 73%, 91%, 62%, 36%, 70% and 7%, respectively.Detection of the resistance genes(cfr, fex A and fex B) were performed for the 11 florfenicol-resistant strains. Of all these strains, cfr were negative, 3 was fex A single positive, one was fex B single positive, 7 was fex A+fex B double positive. Plasmid conjugation and transformation experiments showed that the conjugation can occur for the plasmid carrying fex A gene, while the transformation can occur for the plasmid carrying fex B gene. Characteristics of fex A and fex B gene haboring on the plasmids contribute to the occurrence of horizontal transfer. The Genetic environment analysis of fex B showed that fex B gene was embeded in two novel inverted repeat insertion sequence, which is designated ISEfa14. The function of composite transposon by these insertion sequence formed need further confirmation.13 esp-positive strains was detected in enterococci from humans, pigs and food. Of them, 7 enterococci strains from Humans belonged to ST4, one belonged to ST116; one enterococci strains from pigs belonged to ST4, one strain were not typed; 2 enterococci from food source belonged to ST16, one belonged to ST69. There is a common MLST type(ST4) among Enterococcus faecalis from humans and pigs, indicating that there is the possibility of transmission among these strains. Therefore, the resistance and pathogenicity of these strains deserves further attention.In summary, the resistance situation of enterococci from the different sources(human, swine, fresh meat and food) in Henan Province were investigated in this study. Then, the resistance mechanism of enterococci to florfenicol were explored. A new insertion sequence ISEfa14 was identified, which provides partial theoretical explanation for horizontal transfer of fex B gene.