Dietary Bacillus subtilis Group Reduces the General Infection of Salmonella Pullorum in Broiler Chicken

Background:Salmonella enterica subsp. enterica serovar Gallinarum biovar Pullorum (Salmonella Pullorum) is a specific avian pathogen responsible for Pullorum disease, causing substantial economic losses to the global poultry industry. With the rising restrictions on antibiotic use, probiotics have emerged as promising therapeutic alternatives. The Bacillus subtilis group, including B. amyloliquefaciens and B. subtilis, is a collection of closely related species that has been widely used as a probiotic due to its broad-spectrum antimicrobial activity and other benefits. However, how the probiotics-derived antibacterial phenotype contributes to infection control is still unclear. Methods: In this study, we used two different antibacterial phenotype strains, B. amyloliquefaciens and B. subtilis, to treat S. Pullorum infections. The spores of two strains (10⁷ CFUs) were supplemented daily for 21 days. Results: The reduction in body weight gains and the severity of S. Pullorum-induced symptoms were ameliorated. Compared to B. subtilis, B. amyloliquefaciens exhibited a stronger host protection effect, manifested in a greater reduction in the bacterial load of S. Pullorum in organs throughout the infection. Furthermore, both strains enhanced cecal microbiota diversity, suppressed infection-associated taxa, and promoted beneficial genera. Conclusions: Our findings demonstrate that probiotic Bacillus can alleviate S. Pullorum infection and improve growth performance in poultry, especially the antimicrobial phenotype contributing to pathogen clearance. This work provides crucial insights for developing effective, probiotic-based strategies against Pullorum disease.