Characterization of Salmonella isolated from donkeys during an abortion storm in China

In China, abortions of donkeys caused by Salmonella have dramatically stifled the growth of the donkey industry. However, pathogenicity of Salmonella linked to abortions in donkeys has not been previously described. Bacteria were isolated and identified from 45 donkeys that experienced abortions, and antibiograms were conducted. Pathogenicity, as median lethal dose (LD₅₀) in mice was then determined. Furthermore, a mouse abortion model was used to re-create the disease observed in donkeys. The pathologic changes in spleen, liver, intestine and embryo were observed by histological examination. An immunofluorescence assay was used to determine the location and distribution of Salmonella colonization in tissues. A clear link was made between S. abortus equi and abortions in donkeys. The bacterial strains isolated from these cases were either highly or moderately sensitive to the 8 antibiotics tested here. The strain of S. abortus equi isolated here was lethal to mice (LD₅₀ value is 1.88 × 10⁸ CFU), and caused abortions in pregnant mice. The 50% abortion-causing dose was 1.22 × 10⁸ CFU. Pathological and immunofluorescence data confirmed that the abortions in pregnant mice and donkeys were accompanied by similar disease processes. Therefore, a Salmonella induced abortion model in mice was developed, characterized by abortion, aberrant embryo development, and parenchymal hypoplasia. The mouse abortion model developed here is an important tool for the future characterization and testing therapeutic interventions.