| Colibacillosis caused by Escherichia coli(E.coli)is one of the most clinically common chicken bacterial diseases.A large amount of incidence and considerable economic losses caused by E.coli should be taken seriously.At present,colibacillosis is a serious disease in some chicken farms and a large number of antibiotics was used for treatment,resulting in the continuous expansion of the drug resistance spectrum of E.coli and formation of a vicious cycle.At the same time,the residues of drugs in livestock pose potential threats to the sustained development of poultry industry and human health.For a long time,colistin have been widely used as feed additives for growth promotion and disease prevention of livestock in many countries,while colistin is the last line of defense against fatal infections caused by gram-negative pathogens.In recent years,with the increasing drug resistance problem,the use of colistin faces serious challenges due to the emergence of colistin-resistant gene in the plasmids(especially mcr-1).Therefore,focusing on the actual development of the current poultry industry,the resistance monitoring of E.coli,especially the resistance to colistin should be carried out,it will be conducive to understanding the occurrence and development of E.coli resistance,and will provide a better scientific basis for the veterinary clinical medication.In this study,the liver tissues of diseased chickens in Tai’an were collected.130 isolates of E.coli were isolated using bacterial culture characteristics tests,PCR and microbiology identification system.Then,the susceptibility to colistin was determined by trace broth dilution method.Molecular detection of colistin resistance genes was performed by PCR.The drug resistance phenotype of E.coli was analyzed by disk diffusion method.The relationship between E.coli resistance and a variety of drug resistance genes was analyzed.The results are as follows:1.A colistin susceptibility test was used to initially screen the strains,and then we use the E.coli bacteria solution as a conventional PCR template to detect four colistin resistance genes(mcr-1,mcr-2,mcr-3,mcr-4).PCR results showed that 75(58%)isolates carriedmcr-1 genes among the 130 E.coli isolates;the other three colistin resistance genes,mcr-2,mcr-3 and mcr-4,were not detected in this study.These results indicate that the colistin resistance gene mcr-1 has been widely distribution in chicken-derived E.coli in Tai’an aera.2.The susceptibility test of six types of 12 antibacterial drugs was performed on 130 E.coli isolates using K-B disc diffusion method recommended by CLSI.The results showed that130 isolates showed different degrees of resistance to 12 antibiotics,and the drug resistance to Nalidixic acid(NA)was 100%,tetracycline(TE)95%,ampicillin(AMP)91%,cefotaxime(CTX)89%,streptomycin(S)88%,ceftriaxone(CRO)87%,Doxycycline(DO)86%,Chloramphenicol(C)85%,Levofloxacin(LEV)77%,Sulfamethoxazole/trimethoprim(SXT)69%,Gentamicin(CN)57%,Amikacin(AK)23%.The statistical results show that seven isolates were resistant to at least three antibiotics.Among them,two isolates were resistant to four antibiotics and the others had resistance to at least five antibiotics.All E.coli isolates from chickens in the Tai’an area are multi-drug resistant and the drug resistance is very serious.3.Partial resistance genes of β-lactams,aminoglycosides,tetracyclines,and sulfonamides were detected by PCR and further analyzed the spread of other resistance genes in E.coli from chickens.The results showed that the detection rates of β-lactam drug resistance genes CTX-M,SHV,and TEM were 53.8%,3.1% and 90.0%,respectively.The detection rates of aminoglycoside resistance genes aphA3,aacC2,aadA and aacC4 were55.4%,20.8%,0% and 0% respectively.Tetracycline resistance genes tetA,tetB,tetC and tetD were 82.3%,13.8%,98.4% and 0%,respectively.Sulfa resistance gene sul1,sul2,and sul3 were 63.8%,41.5% and 0%,respectively.A total of ten drug resistance genes were detected.Four drug resistance genes,aadA,aac C4,tetD and sul3,were not detected.4.The results show that the rate of carrying both the β-lactam resistance gene and mcr-1is 94.7%(71/75).The rate of carrying mcr-1 and aminoglycoside resistance gene was 78.7%(59/75),and all isolates carried mcr-1 and tetracycline resistance gene.The ratio of carrying mcr-1 and sulphonamide resistance genes was 76.0%(57/75).This indicates that E.coli strains harboring the colistin resistance gene mcr-1 often carries other resistance genes.The isolation and identification of chicken E.coli in this study laid a foundation for the epidemiology of E.coli in Tai’an.The drug susceptibility testing carried out on the isolatesprovided the scientific basis for clinical treatment and prevention of E.coli in chickens in Tai’an.In addition,the monitoring of colistin and other multiple drug resistance genes indicates that many drug resistance genes,especially ESBL normally carried the mcr-1,which should be highly concerned. |
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