Characterization of a Salmonella strain isolated from Tibetan blue sheep

Considering the ecological importance of blue sheep and the lack of information regarding their infection status, this study aimed to determine the causes of diarrhea and death in blue sheep in the Shigatse region. A key strain that caused diarrhea and even death in blue sheep was isolated from fecal samples and analyzed using morphological observation, biochemical tests, 16S rRNA genetic analysis, mouse pathogenicity tests, and drug susceptibility tests. The strains were grouped into pairs, short chains, or Gram-negative bacilli. The biochemical results were consistent with those obtained for Salmonella spp. The 16S rRNA sequence shared 100 % homology with Salmonella sequences in the NCBI database. The results indicated that the isolated strain was Salmonella, which was named G1GX051. G1GX051 showed strong pathogenicity upon intraperitoneal injection of 1.0 × 10⁴, 1.0 × 10⁶, 1.0 × 10⁸ CFU/mL bacterial solutions (0.2 mL) to SPF grade mice (six per group). Notably, the entre group inoculated with 1.0 × 10⁸ CFU/mL died within 6 days of injection. Anatomical analysis revealed necrotic foci on the liver surface, spleen swelling, a dark red and distended stomach, intestinal congestion, thinning of the intestinal wall, and a firm and congested ileocecal valve. Histopathological analyses revealed spleen and kidney congestion, as well as inflammatory cell infiltration. Drug sensitivity analysis indicated that G1GX051 was resistant only to erythromycin. Overall, G1GX051 isolated from blue sheep with diarrhea was resistant to erythromycin but responsive to several other medicines, indicating the need for monitoring bacterial resistance in wildlife.