Heat-Inactivated Bacillus can Against Novel Duck Reovirus Infection In vitro and In vivo.

The novel duck reovirus (NDRV) poses a significant threat to the poultry industry, with limited effective treatment options and no effective vaccine available. As the dominant genus of Bacillus in the duck intestine, its antiviral effects, particularly in a heat-inactivated form, have been previously reported. In our study, we used the NDRV-infected duck embryo fibroblast (DEF) cells and a Cherry Valley duck model to evaluate the antiviral properties of heat-inactivated Bacillus. Four strains of probiotics were isolated from healthy duck feces, namely Bacillus subtilis (B. subtilis) Bac28, Bacillus tequilensis (B. tequilensis) Bac41, Bacillus subtilis (B. subtilis) Bac45, and Bacillus licheniformis (B. licheniformis) Bac55, all exhibiting probiotic properties. In an in vitro assay, the cytotoxic effectsi of heat-inactivated isolates on DEF cytotoxicity were assessed using the CCK-8 assay. Furthermore, the anti-NDRV activities of heat-inactivated solutions of these four strains were evaluated through RT-qPCR. Additionally, the mRNA relative expression levels of inflammatory factors such as TNF-α, IL-1β, and IL-6, as well as ZO-1 and occluding, were examined using RT-qPCR. The results demonstrated that the heat-inactivated solution exhibited no cytotoxicity and displayed inhibitory effects against NDRV in DEF cell cultures. Treatment with the heat-inactivated solution significantly down-regulated inflammatory cytokine levels and up-regulated mRNA expression levels of intestinal barrier factors. In the in vivo tests, the heat-inactivated Bacillus mixture effectively alleviated clinical symptoms and intestinal damage of ducks infected by NDRV. These findings suggest that the four probiotic strains could provide some levels of protective effects against NDRV infections.