Mastitis causes significant economic losses to the dairy industry. Escherichia coli (E. coli) is considered a primary cause. The study aimed to investigate the antibiotic resistance profiles and presence of virulence genes in E. coli isolated from milk samples collected from cows with clinical mastitis on a large dairy farm in Hetian, southern Xinjiang, China. E. coli was detected in 26.9% of milk samples from 130 cows with clinical mastitis. Multilocus sequence typing (MLST) revealed that the dominant sequence lines were ST1121, ST88, and ST58. A total of 34.3% of the isolates were multidrug-resistant; all isolates were completely resistant to penicillin and lincomycin, and highly resistant to ampicillin (80.0%). All isolates carried the transcription-repair coupling factor (Mfd) and various efflux pump resistance genes. Aminoglycoside resistance genes were fully consistent with the corresponding resistance phenotypes. Except one isolate, all the remaining 34 isolates carried multiple virulence genes, including 33 carrying the curli gene. Notably, the fecI gene, associated with reduced virulence in bovine mastitis, was detected in 94.3% of isolates. This study shows that the E. coli strains responsible for clinical mastitis in this dairy farm are dominated by the ST1121 lineage, which exhibits pronounced multidrug resistance (MDR) and distinctive virulence gene profiles, suggesting multiple sources of infection. This provides a molecular basis for targeted antibiotic treatment and prevention of E. coli mastitis in the dairy farm in southern Xinjiang. This study offers a reference for the control of mastitis in dairy cattle in northwestern China.

To Cite This Article: Cai J, Yang D, Qin S and Chen F, 2026. Antimicrobial resistance and virulence genes of Escherichia coli isolated in a large-scale dairy farm from clinical mastitis in Southern Xinjiang, China. Pak Vet J, 46(4): 830-838. http://dx.doi.org/10.29261/pakvetj/2026.080