Genomic characterization of four Salmonella-specific bacteriophages and evaluation of their cocktail efficacy in milk

Bacteriophages offer a promising solution for controlling multidrug-resistant Salmonella in food matrices. This study analyzed the genomic, proteomic, and functional characteristics of four bacteriophages (STP-1, STP-2, STP-3, and STP-4) targeting Salmonella Typhimurium. Genomic analysis revealed lysis-related genes, including holin, endolysin, and RZ-like spanins, with no genes linked to human toxicity or antibiotic resistance. Unique genomic features, such as viral integrase family 4 and/or tRNA genes, suggest functional and evolutionary diversity. Proteomic and phylogenetic analyses classified the phages within the Guernseyvirinae, Casjensviridae, and Ackermannviridae families. Cytotoxicity tests showed no significant differences at high phage concentrations than control cells (> 10 log PFU/mL, P > 0.05). A phage cocktail targeting S. Typhimurium strains applied to milk (MOI 1,000) reduced bacterial counts by 2.11 log CFU/mL after 7 days, greater than same phage cocktails on chicken breast in a previous study. These findings demonstrate the superior efficacy of multi-strain phage cocktails as versatile biocontrol agents, particularly in milk.