In this study, we collected 565 fecal samples from free-range Tibetan yaks to examine whether these animals can serve as a reservoir for pathogenic and antimicrobial-resistant Escherichia coli. The antimicrobial sensitivity testing of each resulting isolate was evaluated according to the disk diffusion method, whereas PCR analysis was performed for detection of resistance and virulence genes. Additionally, strains containing extended-spectrum beta-lactamases (ESBLs) genes were initially identified via the double-disk synergy method and confirmed by PCR analysis. Of the 488 E. coli isolates examined, approximately 31.1% were multidrug resistant. OmpA (30.2%) and etrA (23.1%), and bla_CTX-M (27.6%) and bla_TEM (14.4%) were the mainly prevalent virulence and drug resistance genes, respectively. Notably, we detected the CTX-M type but not the SHV type among the ESBL-producing strains and there was a significant association between resistance and virulence genes for aac(3)-lla, bla_TEM/ompA, bla_CTX-M/etrA, and cmlA/cnf1 (P<0.05). Lastly, the majority of the strains belonged to phylogroup A (72.7%). This is the first report of the occurrence of pathogenic and antimicrobial-resistant ESBL-producing E. coli strains in free-range Tibetan yaks.

Key words: Antimicrobial-resistant, Disk diffusion method, Double-disk synergy method, Escherichia coli