| Summary: | <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Derby (<i>S.</i> Derby) is one of the numerous non-typhoidal <i>Salmonella</i> serovars and has been recognized as a food-borne pathogen. In 2019, outbreaks of salmonellosis were reported in 13 yak farms in the Aba Tibetan Autonomous Prefecture, China. A total of 32 salmonella strains were isolated from 162 fecal samples of yaks with diarrhea as well as from drinking water samples. The isolates were subjected to serovar identification, animal experiments, and whole-genome sequencing (WGS) analyses. The serovar of all the isolates was <i>S.</i> Derby, and the sequence types (STs) were ST40. The analysis of the differences of single-nucleotide polymorphisms (SNPs) showed that the salmonella strains isolated from 13 farms were clonally related. Animal experiments showed that the lethal dose (LD<sub>50</sub>) was 4.57 × 10<sup>7</sup> CFU (colony-forming units); the shedding time of <i>S.</i> Derby in mice was 24 days; the bacterial loads in spleen were higher than those in other organs (ileum, liver, and cecum). Pathological analyses by hematoxylin and eosin (H&E) staining revealed obvious damage in the spleen, liver, and intestine. These results indicate that the <i>S.</i> Derby from yaks can cause infection in mice.
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