Host-associated Bifidobacterium longum exhibit gastrointestinal resilience and antagonistic activity against...

Probiotics are increasingly explored as alternatives to antibiotics for preventing and controlling infectious diseases in livestock, including enteritis, pneumonia, and sepsis. However, most commercially available probiotic strains originate from humans, which can limit their colonization efficiency and functional performance in livestock due to host-specificity. In this study, we isolated twelve Bifidobacterium longum strains from healthy dairy calves and evaluated their probiotic potential with a focus on gastrointestinal resilience and antimicrobial activity. Comparative genomic and phylogenetic analyses revealed that these bovine-derived isolates form a distinct genetic lineage, separated from previously reported human-, animal-, and food-derived strains, highlighting their host-specific evolution. In vitro stress tolerance assays showed that all isolates maintained high viability under simulated gastric fluid, low pH, bile salts, lysozyme exposure, and hyperosmotic conditions. The strains exhibited robust colonization and adhesion capability, based on cell surface hydrophobicity, auto-aggregation, mucin adhesion, and biofilm formation. Antimicrobial activity and competition assay indicated that several B. longum strains effectively inhibited Salmonella enterica serovars Typhimurium and Dublin. These findings indicate that host associated B. longum strains possess enhanced gastrointestinal survival and potent antagonistic activity against major enteric pathogens, thereby representing promising next-generation probiotic candidates for improving intestinal resilience.