Isolation and Characterization of Bacteriophage SSU5 Specific for Salmonella enterica serovar Typhimurium Rough Strain

Abstract

Salmonella sp. is a major food-borne pathogen causing a variety of diseases. Use of bacteriophage for control of foodborne pathogen is a newly promising way as an alternative antibiotic therapy. Previously, our group has isolated several phages specific for S. Typhimurium to develop phage cocktail for Salmonella biocontrol. However, most of them bind only one of 3 types of the cell surface structure: BtuB, O-antigen (O-Ag) and flagella. Using the ΔbtuB and the ΔbtuB ΔrfbP double mutant strains of Salmonella as a host, I isolated SSU5 phage that does not use BtuB, O-antigen, or flagella as a receptor. TEM analysis showed that SSU5 belongs to the family Siphoviridae and genomic analysis revealed that SSU5 contains a linear dsDNA consisting of 103, 229 bp with a G+C content of 51.11%. The genome of SSU5 showed high homology to that of cryptic plasmid pHCM2 harbored by Salmonella Typhi strain CT18, and 72 out of 130 predicted ORFs were annotated as hypothetical proteins, supporting the novelty of this phage. The inhibition of SSU5 adsorption to the periodate treated-bacteria allowed me to hypothesize that the rough lipopolysaccharide (LPS) may be the host receptor for SSU5, and it was verified by a spotting assay on the mutants that have various truncations in their core LPS. Analysis of the receptor of SSU5 revealed that this phage would be a promising tool as a phage cocktail component to control rough strains of S. Typhimurium generated by mutation or phase variation.