Probiotic potential of Bacillus velezensis MZ-09: Assessing characteristics and safety through in vitro and in vivo analyses.

The global overuse of antibiotics, including prescriptions in human medicine and routine prophylactic use in livestock farming, has intensified the antibiotic resistance crisis, necessitating urgent research and development of alternatives for reducing associated health and environmental risks. This study investigated the biological characteristics and bio-safety of Bacillus velezensis MZ-09 isolated from Min pigs with strong stress resistance via in vitro methods, whole-genome sequencing and in vivo methods. The in vitro experiments demonstrated that the Bacillus velezensis MZ-09 exhibits strong tolerance to NaCl, bile salts, and artificial digestive fluids, along with favorable antibacterial activity against pathogenic bacteria and no hemolytic activity. Particularly, it exhibits no resistance to commonly used antibiotic drugs. Whole-genome analysis revealed that Bacillus velezensis MZ-09 harbors diverse genes for carbohydrate and amino acid metabolism, exhibits robust energy metabolism capabilities, and has safety characteristics. In the broiler experiments, dietary supplementation with 500 mg/kg of MZ-09 freeze-dried powder (1.0 × 10 CFU/g) significantly improved the growth performance and meat quality parameters as well as enhanced broiler immunity by increasing serum immunoglobulin levels. Furthermore, Bacillus velezensis MZ-09 promotes host health by modulating intestinal morphology, reducing inflammatory cytokine levels, increasing short-chain fatty acid concentrations, and regulating the gut microbiota. In conclusion, these findings identified that Bacillus velezensis MZ-09 as a promising probiotic candidate with dual functionality in the safety of animal-derived food products enhancement and antibiotic dependency reduction.