Antimicrobial resistance, virulence gene, and biofilm formation of Escherichia coli isolated from yaks in Qinghai, China.

INTRODUCTION

This study investigated the antimicrobial resistance (AMR), virulence gene profiles, and biofilm formation capabilities of Escherichia coli (E. coli) isolated from yaks in Qinghai, China.

METHODS

A total of 60 isolates were analyzed for resistance against 11 antibiotics. PCR was used to identify antibiotic resistance genes (ARGs) and virulence genes. Biofilm formation was assessed via phenotypic assays. Phylogenetic typing and serotyping were performed using standard molecular and immunological methods.

RESULTS

High prevalence of multidrug resistance (MDR) was observed, particularly to tetracyclines (43.33%), ciprofloxacin (33.33%), and cefotaxime (33.33%). A total of 63 ARGs were identified, with bla EC-18 (85%) being the most prevalent. Virulence gene screening detected 253 factors, including csgA, csgC, and entD (100% prevalence). Biofilm assays showed that 40% of isolates were strong biofilm producers. Phylogenetic typing classified most strains as phylogroup B1 (81.67%), with sequence types ST2522 (8.33%) and ST56/ST10 (5% each) being dominant. Serotyping revealed O25 and O107 as the most common serotypes (16.67% each). Strong biofilm formers exhibited higher ARG diversity, including bla EC-18 (79.17%) and sul1 (41.67%).

CONCLUSION

Overall, these findings identify diarrheic yak‑associated E. coli as a potential reservoir of resistance and virulence determinants, and support strengthened antimicrobial stewardship, farm hygiene, and One Health surveillance in the Qinghai‑Tibet Plateau.