Drug Resistance Patterns And ESBLs Gene Analysis In Escherichia Coli Isolated From Livestock In Chongqing Area

The development of Escherichia coli drug resistance is closely related to its characteristics,the spread of drug-resistant plasmids and the use of antibiotics.The emergence of multiple drug-resistant strains makes the drug resistance of E.coli more and more serious.The extended-spectrum ?-lactamases(ESBLs)is one of the most important mechanism for the resistance to cephalosporins in Gram-negative bacteria.E.coli carried the ESBLs genes has been regarded as the important public health issues because of its great threat posed to human and animal healthy.In this study,the drug resistance patterns and ESBLs genes were analyzed in E.coli isolated from clinical livestock,to provide a basis for evaluation of the current situation of bacterial resistance of livestock and poultry in Chongqing area and the patterns of ESBLs resistance genes.A total of 1455 E.coli isolates were obtained from chicken,swine and bovine in 13 farms located in seven districts in Chongqing from 2014 to 2016.The drug resistance patterns,multidrug resistant genes,ESBL gene patterns were analyzed for all the isolates.Also,MLVA genotyping methods were evaluated and carried out for some of the isolates.The main results are as follows:(1)Among the 28 tested antibiotics,all the 1455 isolates were resistant to one or more drugs,the drug resistant rate is ranging from 1.1%to 89.1%.The experimental bacteria were most sensitive to imipenem of carbapenems and amikacin of aminoglycoside,the resistance rate is only 1.1%and 5.4%,respectively.Amoxicillin resistance was the most serious,with an average resistance rate of 89.10%.All isolate were presented relatively high drug resistance to apramycin(45.5%),tetracycline(68.8%),florfenicol(55.9%) and nalidixic acid(46.1%),respectively.The resistance of E.coli isolates from bovine to aminoglycosides and quinolones was less than 5%,and they were 100%sensitive to norfloxacin.(2)The multi-drug resistance was obvious in all the isolates,15.7%,17.6%,27.7%,22.7%,15.1%and 1.2%of the isolates were resistant to 0-5,6-10,11-15,16-20,21-25 and 26-28 kinds of drugs.One isolate from a swine farm was resistant to 28 kinds of drug,no isolate resistant to 29 or 30 kinds of drugs;one isolate from a bovine farm was sensitive to all the tested drugs.Generally,isolates from chickens are more resistant to drugs than isolates from swine or bovine,and isolates obtained in winter and spring are more resistant to drugs than isolates from summer and autumn.There was no significant difference in the drug resistance rate of chicken isolates in different districts and counties,but there was a certain difference in the drug resistance rate of pig isolates in different farms.(3)Among all the 1455 isolates,96.1%(1398/1455)isolates carried one or more ESBL genes,which results in 12 kinds of ESBL gene patterns.blaTEM and blacTx-M genotypes were the most extensively existed ESBL pattern in farms in Chongqing area.blaTEM genotypes(59.3%)were the highest,and blaTEM+cTx-M(21.9%)genotypes were the next.(4)Ten loci MLVA genotyping analysis was carried out in 399 isolates from chicken and swine during 2014-2015.6 loci combination(GECM-6)with high discriminatory power was selected for genotyping the E.coli isolates in Chongqing area.The evolution tree was constructed based on the 10 loci MLVA results,and 263 genotypes were obtained.The MLVA genotypes were highly disperse,no predominant genotype was identified.The isolates showed polymorphisms at the genetic level,and the isolates genotypes in different regions showed significant differences.In conclusion,this study systematically analyzed the source,season and drug use of 1455 E.coli isolates,revealed the drug resistance status,law and multiple drug resistance of livestock and poultry in Chongqing area,and provided a basis for guiding clinical drug use.Twelve gene types of ESBLs-producing E.coli were detected in Chongqing area,with blaTEM and blaCTX-M were dominant genotypes,which provided theoretical guarantee for rational drug use.New combinations of 6 MLVA loci with high resolution(GECM-6)were selected,which were suitable for routine genotyping detection and epidemiological investigation of E.coli in livestock and poultry in Chongqing and even southwest China,providing technical support for the source tracing of E.coli caused diseases.Control and reduce the production of multiple drug-resistant strains from the source.