Multidrug resistance, biofilm formation, and pathotype diversity of Escherichia coli isolated from diarrheic lambs in intensive sheep farms, Aksu, Xinjiang, China

Under the One Health framework, the antimicrobial resistance and pathogenicity of Escherichia coli isolated from diarrheic lambs pose a potential threat to public health security. Aksu in Xinjiang is a major intensive mutton sheep breeding base in China. This study aimed to investigate the antimicrobial resistance, virulence gene carriage, biofilm-forming ability, pathotype distribution and phylogenetic group characteristics of E. coli from diarrheic lambs in this region, and analyze their potential correlations. A total of 150 samples were collected from diarrheic lambs in 6 intensive mutton sheep farms. E. coli was isolated and identified via differential media and specific gene detection; the disk diffusion method was used for antimicrobial susceptibility testing. PCR was performed to detect resistance and virulence gene carriage, and E. coli pathotypes were determined based on molecular characteristics. Mouse challenge assay was adopted to evaluate bacterial pathogenicity, crystal violet staining to assess biofilm-forming ability, and PCR to conduct phylogenetic group typing. A total of 121 E. coli strains were isolated with an isolation rate of 80.7%, including 38.0% multidrug-resistant (MDR) strains and 49.6% pathogenic strains (5 single pathotypes and 7 hybrid pathotypes). Mouse models showed all tested pathogenic strains had pathogenicity. Phylogenetic group analysis showed that group B1 was the predominant phylogroup (76.0%). Moreover, 78.6% of the strains had biofilm-forming ability, and MDR strains exhibited significantly higher biofilm-forming ability than non-MDR strains. The isolated strains harbored abundant resistance and virulence genes, with 13 different types of resistance genes and 18 virulence genes with distinct functions detected in total. This is the first systematic report on the diversity characteristics of pathogenic E. coli from diarrheic lambs in intensive sheep farms in Aksu, clarifying the phylogenetic and antimicrobial resistance characteristics of the strains and revealing a significant association between biofilm formation and bacterial resistance. These findings provide a basis for the coordinated management of cross-domain public health risks in underdeveloped regions under the One Health framework, and contribute to the sustainable development of the mutton sheep industry and the safeguard of public health security.