Functional and Genomic Features of a Lytic Salmonella Phage vB_StyS_KFSST1 for Development as New Feed Additive

Lytic phages have emerged as promising candidates for feed additives for controlling <i>Salmonella</i> in poultry, owing to their high specificity, self-replication, and excellent stability. According to the European Food Safety Authority (EFSA) guidelines, their application as feed additives requires evaluation of safety, host range, <i>in vitro</i> and <i>in vivo</i> efficacy, and stability. Thus, this study aimed to evaluate the functional and genomic features of vB_StyS_KFSST1, previously isolated from poultry processing wastewater, as a candidate for the development of a new feed additive against <i>Salmonella</i>. The phage exhibited dual serotype-specific lytic activity against <i>S.</i> Enteritidis and <i>S.</i> Typhimurium, with high plating efficiency. Infection kinetic analysis revealed its rapid adsorption and a sustained inhibitory effect lasting up to 12 h for both serovars. Whole genome sequencing of the phage was performed using the Oxford Nanopore PromethION 2 Solo platform. The phage genome consisted of 47,149 bp dsDNA, containing 98 open reading frames and two tRNA genes. No lysogeny-related, antibiotic resistance, or virulence-associated genes were found in its genome, whereas phage-susceptible <i>Salmonella</i> strains carried multiple antibiotic resistance and virulence genes. Phylogenetic and taxonomic analyses finally clustered the phage with other lytic <i>Salmonella</i> phages, classifying it within the genus <i>Skatevirus</i>. These findings highlight the potential of lytic phage vB_StyS_KFSST1 as a promising candidate for the development of a feed additive to control <i>Salmonella</i> in poultry husbandry.