Identification of canine Escherichia coli epidemic strains in Xinjiang， their drug resistance characteristics， and virulence gene detection

【Objective】 To identify canine Escherichia coli epidemic strains in Xinjiang， analyze their drug resistance characteristics and virulence genes， which could provide theoretical basis for targeted prevention and control of canine drug-resistant strains as well as rational clinical medication in Xinjiang. 【Method】 From February to October in 2024， a total of canine anal swab samples were collected in Xinjiang， including 168 samples from healthy dogs and 287 samples from sick dogs. Isolation， identification and molecular typing of canine Escherichia coli were performed. Drug susceptibility and extended-spectrum β-lactamase （ESBLs） resistance genes were subsequently detected. A total of 18 virulence genes were screened by PCR in the 391 obtained Escherichia coli isolates. Strains carrying ≥8 virulence genes were selected for pathogenicity tests in mice. 【Result】 A total of 391 Escherichia coli strains were isolated and identified. Group B1 showed the highest detection rate， followed by group A and group B2， while group D had the lowest rate. Canine Escherichia coli exhibited the highest drug resistance rate to ampicillin （a β-lactam antibiotic）， followed by cefotaxime and tetracycline.The detection rate of multiple drug-resistant strains （resistant to ≥3 classes of antibiotics） reached 66.75%. No significant difference was observed in the multiple drug resistance against 15 antibiotics between Escherichia coli strains from healthy dogs and sick dogs （P>0.05）. According to PCR detection，among the four ESBLs resistance genes in ESBLs-producing strains， TEM gene had the highest carrying rate， followed by CTX-M gene， while SHV and OXA genes presented relatively low detection rates. A total of 12 virulence genes were detected in the 391 canine Escherichia coli strains. The detection rate of ompA gene was the highest， followed by ibeB， sodA， yijP， mat， fimH and iroN genes. Pathogenicity assays in mice revealed distinct virulence among different epidemic strains. 【Conclusion】 The canine Escherichia coli epidemic strains in Xinjiang belong to group A and group B1. Severe drug resistance and widespread multidrug resistance are observed in these strains. Most strains carry ESBLs resistance genes and multiple virulence genes with strong pathogenicity. ESBLs-producing canine Escherichia coli strains have likely spread extensively among pet dogs in Xinjiang， posing a serious threat to public health security.