Genomics of Salmonella phage ΦStp1: candidate bacteriophage for biocontrol

Multidrug-resistant Salmonella causing Salmonellosis is a food-borne pathogen and hence a public health hazard. Alternatives to antibiotics, such as phages, are possible solutions to this increasing drug resistance. In this context, several Salmonella phages were isolated and characterized. This paper describes the physiochemical and whole genome characterization of one such bacteriophage, ΦStp1, which efficiently infects serovars Salmonella Enteritidis and Salmonella Typhimurium. Morphological observations by transmission electron microscopy and phylogenetic analysis using terminase gene classified ΦStp1 to family Siphoviridae, closely resembling 'T5 like phage' morpho-types. With a maximum adsorption time of 50 min, ΦStp1 latent period was 30 min with 37 phages/cell burst size. ΦStp1 draft genome sequenced by shotgun method comprised 112,149 bp in 3 contigs with 37.99% GC content, 168 predicted ORFs, and 15 tRNAs. Genes involved in host shut down, DNA replication, regulation, nucleotide metabolism, lysis, and morphogenesis were also noted. The study not only provided an insight into the characteristics of phage genome, but also information about proteins encoded by bacteriophages, therefore contributing to understanding phage diversity. Sequence analysis also proved the absence of virulence and lysogeny-related genes, which only went to confirm ΦStp1 as a promising therapeutic agent against Salmonella infections.