Characterisation of Yersinia pseudotuberculosis bioserotype 1/O:2b ST16 causing a bovine mastitis infection in a dairy cow in Germany

Introduction The zoonotic bacterium Yersinia pseudotuberculosis (YPS) primarily causes gastrointestinal and extraintestinal diseases in animals, but can also infect humans. Due to the concerted action of a broad spectrum of virulence determinants associated with an infection by YPS, the host specificity of certain phylotypes and determinants affecting the epidemiology of the disease are still poorly understood. In 2025, a case of mastitis of a cow in Germany was attributed to YPS, with the bacterium being isolated at various time points. Methods The isolates were analysed in-depth using classical and whole-genome-based approaches to reveal their phenotypic and genetic properties. Results Mastitis was caused by a single strain (25-YE00352) of the bio/serotype 1/O:2, which belongs to multilocus-sequence type ST16 (phylotype). Except for the Yersinia adhesion pathogenicity island YAPI, the genome of 25-YE00352 lacked other main virulence factors, including the pYV virulence plasmid, the YPS-derived mitogen superantigen, and the pathogenicity island HPI. Phylogenetically, 25-YE00352 resembles isolates recently described from wildlife and captive animals in Germany. Conclusion To the best of our knowledge, this is the first report from Germany on a YPS isolate recovered from a chronic case of mastitis in a cow.