Multidrug-resistant mammary pathogenic Escherichia coli ST479 isolated from Holstein dairy cows in Jiangsu, China

Mastitis is one of the most prevalent diseases in dairy cattle farming, causing significant economic losses to the industry. Escherichia coli ( E. coli ) is a major infectious pathogen responsible for bovine mastitis. This study conducted molecular and phenotypic characterization analyses of E. coli strains isolated from milk samples of clinical mastitis cases in Jiangsu Province, China. Through antibiotic susceptibility testing, multilocus sequence typing (MLST), whole-genome sequencing analysis, and comparative assessment of mammary pathogenicity in cellular and murine models. The results demonstrate that E. coli ST479 is a multidrug-resistant mastitis-causing strain capable of producing extended-spectrum β-lactamases (ESBLs) and exhibits a globally widespread distribution. In experimental models, ST479 invaded bovine mammary epithelial cells and induced mastitis in mice. Notably, it elicited a moderated inflammatory response compared to the reference strain ATCC 25922, suggesting a distinct host-pathogen interaction profile The emergence of multidrug-resistant clonal strains such as ST479, capable of causing mastitis and producing ESBLs, represents a concern for dairy farm health management due to its potential to limit treatment options. Given the detection of ST479 in multiple regions around the world and its multiple antibiotic drug resistance, we emphasize the need for enhanced surveillance and management of such strains in dairy farms to safeguard animal health and ensure sustainable production.