Molecular Epidemiology and Antibiotic Resistance Associated with Avian Pathogenic Escherichia coli in Shanxi Province, China, from 2021 to 2023

<i>Avian Pathogenic Escherichia coli</i> (APEC) constitutes a major etiological agent of avian colibacillosis, which significantly hinders the development of the poultry industry. Conducting molecular epidemiological studies of APEC plays a crucial role in its prevention and control. This study aims to elucidate the molecular epidemiological characteristics of <i>Avian Pathogenic Escherichia coli</i> in Shanxi Province. In this study, 135 APEC strains were isolated and identified from 150 liver samples of diseased and deceased chickens exhibiting clinical symptoms, which were collected from farms in Shanxi Province between 2021 and 2023. The isolates were then analyzed for phylogenetic clustering, drug resistance, resistance genes, virulence genes, and biofilm formation capabilities. The results revealed that the proportions of the A, B1, B2, and D evolutionary subgroups were 26.67%, 32.59%, 17.78%, and 15.56%, respectively. The drug resistance testing results indicated that 92% of the isolates exhibited resistance to cotrimoxazole, kanamycin, chloramphenicol, amoxicillin, tetracycline, and other antibiotics. In contrast, 95% of the strains were sensitive to ofloxacin, amikacin, and ceftazidime. The most prevalent resistance genes included tetracycline-related (<i>tetA</i>) at 88.15%, followed by beta-lactam-related (<i>bla-TEM</i>) at 85.19%, and peptide-related (<i>mcr1</i>) at 12.59%. The virulence gene analysis revealed that <i>ibeB</i>, <i>ompA</i>, <i>iucD</i>, and <i>mat</i> were present in more than 90% of the isolates. The results revealed that 110 strains were biofilm-positive, corresponding to a detection rate of 81.48%. No significant correlation was found between the drug resistance genes, virulence genes, and the drug resistance phenotype. A moderate negative correlation was observed between the adhesion-related gene <i>tsh</i> and biofilm formation ability (r = -0.38). This study provides valuable insights into the prevention and control of avian colibacillosis in Shanxi Province.