Pathogenicity and Antimicrobial-Resistance Profiles of Escherichia coli Isolated From Faeces of Tibetan Pigs Reared Under Intensive Conditions.

Abstract

BACKGROUND: Intensive indoor pig production systems can foster high antimicrobial exposure and dense animal contact, potentially enriching multidrug-resistant (MDR) Escherichia coli (E. coli) that may enter wider One Health microbial networks. OBJECTIVES: This study investigated grower-finisher Tibetan pigs managed under commercial conditions harbouring phylogenetically diverse E. coli lineages carrying extensive resistance and virulence determinants. METHODS: Between 2021 and 2023, 280 rectal swabs were collected from nine mechanically ventilated farms; the isolated E.coli strains were subjected to phylogrouping, as well as detection of 13 virulence genes and 45 resistance genes, using multiplex PCR. Antimicrobial susceptibility of the isolates to 22 antibiotics was determined by the disk diffusion method. RESULTS: Enteroaggregative E. coli accounted for 27.86% of isolates, and putative STEC/EHEC accounted for 7.14%, with astA being the most prevalent (27.86%). Phenotypically, 94.29% were resistant to amoxicillin and 68.57% to sulfonamides, while 82.86% satisfied the MDR definition; genotypically, tetA (70.71%) and floR (57.14%) dominated the resistance repertoire. Phylogroups A and B1 predominated, but resistance and virulence profiles were dispersed across all lineages, indicating horizontal gene flow rather than clonal expansion. CONCLUSION: Tibetan pigs represent a substantial reservoir of MDR E. coli, strengthening the rationale for farm-level antimicrobial stewardship and integrated surveillance that links animal, environmental and human compartments. The study is limited by its cross-sectional design, focus on a single province and animal host and the absence of parallel human or environmental isolates, which prevent inference of causal zoonotic pathways and should be addressed in longitudinal One Health investigations.