Biological and genomic characteristics of a polyvalent Salmonella phage and its dual application in food decontamination and chick salmonellosis treatment.

Bacteriophages have been widely recognized as one of the most promising alternatives to antibiotics. In this study, a multivalent bacteriophage designated vB_SalM_Sz was isolated, and its whole-genome sequence, biological traits, biosafety profile, and bactericidal activity were comprehensively characterized. Genomic and phenotypic analyses revealed that vB_SalM_Sz is a polyvalent phage capable of lysing both Salmonella spp. and Escherichia coli, taxonomically classified within the genus Rosemountvirus, class Caudoviricetes, family incertae sedis. Phage vB_SalM_Sz exhibited robust stability under broad environmental conditions, including temperatures ranging from 30 to 50 °C, pH values of 3-10, and NaCl concentrations of 0-3 M. Importantly, this phage exerted no hemolytic toxicity and did not impair the viability of mammalian cells. Furthermore, vB_SalM_Sz displayed dose-dependent growth inhibition and bactericidal activity against single cultures of Salmonella, E. coli, and their mixed co-cultures in LB medium, milk, and chicken matrices. The phage treatment significantly improved survival rates in both G. mellonella and chick infection models, while mitigating intestinal tissue injury and suppressing excessive inflammatory responses triggered by Salmonella strain S43 in infected chicks. Collectively, these findings demonstrate the great application potential of the multivalent phage vB_SalM_Sz for the biocontrol of Salmonella and E. coli, laying a solid theoretical and experimental foundation for its further translational development as an antibacterial agent.