Detection Of Drug Resistance Of Escherichia Coli In Calves With Diarrhea In Tongliao Region And Whole Genome Sequencing Analysis Of A Multi-drug Resistant Strain

Pathogenic E.coli is the main pathogen of calf diarrhea,and the massive use of antimicrobial drugs in the clinic makes E.coli resistance more and more serious,which will not only affect the therapeutic effect,but more importantly,there will be more and more drug-resistant strains.In this study,we collected calf diarrhea samples from Tongliao area,isolated and identified E.coli in the samples by using identification media,Gram staining and 16S rRNA sequencing,and determined the MIC of E.coli by micro-broth dilution method;and tested the drug-resistant strains for drug-resistant genes and target mutations;screened a multi-drug-resistant strain for full sequence determination of genome and plasmids,and determined the distribution of drug-resistant genes and their genetic environment.To determine the distribution of drug resistance genes and their genetic environment.The results showed that all 40 isolated E.coli strains with calf diarrhea were resistant to sulfadiazine sodium,enrofloxacin and ciprofloxacin,90% of the isolates were sensitive to polymyxin B.45% of the isolates were resistant to eight tested drugs,and the resistance rates of quadruple to eleven antibiotics ranged from 2.5% to 45%.the detection rates of TEM-1,TEM-206,strA,strB,sul3,qacH and blaCTX genes were detected at 100%,and the detection rates of the remaining resistance genes ranged from 12.5% to 87.5%.40 isolates had target mutations in the gyrA and parC genes,which are common resistance targets of fluoroquinolones,and among them,parC had 56(Ala56Thr),80(Ser80Ile),84(Glu84Lys),and 83(Ser83Leu),87(Gly87Tyr)(Gly87Asp)(Gly87Asn)mutations in gyrA.The sequenced multi-drug resistant strains contained 20 gene islands,1027 virulence genes,and 88 resistance genes,and two plasmids containing 21 resistance genes,with the risk of horizontal transfer risk of horizontal transfer.The results of this experiment show that the level of drug resistance of E.coli in calves with diarrhea in Tongliao area is high,multiple drug resistance exists,and the distribution of drug resistance genes is complicated,and the existence of drug resistance plasmids provides the risk of horizontal transfer of drug resistance genes among bacteria,and this experiment provides a reference for the clinical treatment of E.coli in calves with diarrhea in Tongliao area veterinarians,and also provides a basis for later in-depth studies on the expression of drug-resistant genes under different drug pressures and the horizontal propagation mechanism of plasmids.