Prevalence And Conjugative Transfer Of Transposon In The Multi-drug Resistant E. Coli Isolates From Pigs

Escherichia coli is the most popular pathogenic bacteria in human medicine and veterinary clinic. The prevalence of Escherichia coli will lead serious harm to the development of animal husbandry. Drug resistance, especially multi-drug resistance in bacteria which has been expanded seriously recent years, aroused the public concerns. Transposons are small, mobile DNA sequences that can replicate and insert copies of themselves within chromosome and plasmids. Once transferred on transposons, antibiotic resistance genes have broader opportunities for horizontal spread among different bacterias. Hence, invesitigating the antibiotic resistance, prevalence and conjugative transfer of transposon in multi-drug resistant Escherichia coli strains isolated from swine farms collected in Haerbin, analysising the relationship between the transposon and the multidrug resistance and their co-transferability will help us make clear the mechanism of drug-resistance transferring in gene level, at the same time provid a theory evidence for prevention and the control of Escherichia coli desease.Antimicrobial susceptibility testing of12antimicrobial agents was performed on55Escherichia coli strainsisolated from swine farms using the disk diffusion method of CLSI (2007). The results of the study showed that all the55isolates showed severe drug resisrance. The resistance rates to Sulfamethoxazole compound. Streptomycin were above80%, the resistance rates to Amoxicillin-clavulanate. Gentamicin, Doxycycline, Chloramphenicol, Ciprofloxacin, Enrofloxacin exceeded50%. and the resistance rates to Ceftiofur, Amikacin, Florfenicol were less than50%, the resistance rate to Polymyxin B was0.Meantime all the55isolates presented a multiple drug resistance, the range of the multiple drug was3-11.Using PCR method to amplify the ISEcpl,IS26,tnpA and tnp513and tnpU gene in the55isolates.The results showed that (SEcpl,IS26,tnpA and tnp5I3were amplified successfully, and their detection rates were27.2%,90.9%,50.9%and41.8%, while the tnpU gene was not detected out in this study. Every E coli can be detected one to four kinds of transposon.By the conjugation experiments, we successfully got25transconjugants in the55MDR E.coli strains; the conjugation frequency was56.8%. The range of the resistence was2-8in the25transconjugants,92%of the25transconjugants were multiple drug resistance E coli. Compareing with their parent strains, most transconjugants showed less resistance and demonstrated less presence of transposon genes.5isolates (H1、H5、S5、A2、A9) of the25transconjugants showed the same resistance type and9isolates (H1、H2、H5、S2、S5、S15、S16、A2、A7) of the25 transconjugants demonstrated same presence of transposon genes with their parent strains. Strains H1、H5、S5and A2showed the same resistance type and demonstrated same presence of transposon genes with their parent strains.In these strains, we found multiple drug resistance and transposons were co-transferred compeletly to recipient.In this study we established the method of Quantitative PCR dection of transposon genes ISEcpl,1S26, tnpA and tnp513, futher to compare the absolute copies numbers of these four transposon genes in the parent strains and the transconjugants. Results showed that all transconjugants demonstrate less transposon gene copy numbers than their parental strains.This study successfully invesitigate the level of antibiotic resistanceand the frequency of the multidrug resistance strains carrying transposon in E.coli isolated from swine farms collected in Haerbin, further analysised their conjugation co-tansferability. This study will help us make clear of the mechanism of drug-resistance transferring in gene levelat the same time provid a theory evidence for prevention and the control of Escherichia coli desease.