Isolation, characterization and application of bacteriophage PSDA-2 against Salmonella Typhimurium in chilled mutton

Salmonella is a common foodborne pathogen, especially in meat and meat products. Lytic phages are promising alternatives to conventional methods for Salmonella biocontrol in food and food processing. In this study, a virulent bacteriophage (PSDA-2) against Salmonella enterica serovar Typhimurium was isolated from the sewage and it was found that PSDA-2 belongs to Cornellvirus genus of Siphoviridae family by morphological and phylogenetic analysis. Based on the one-step growth curve, PSDA-2 has a short latent period (10 min) and a high burst size (120 PFU/cell). The stability test in vitro reveals that PSDA-2 is stable at 30-70°C and pH 3-10. Bioinformatics analysis show that PSDA-2 genome consists of 40,062 bp with a GC content of 50.21% and encodes 63 open reading frames (ORFs); no tRNA genes, lysogenic genes, drug resistance genes and virulence genes were identified in the genome. Moreover, the capacity for PSDA-2 to control Salmonella Typhimurium in chilled mutton was investigated. The results show that incubation of PSDA-2 at 4°C reduced recoverable Salmonella by 1.7 log CFU/mL and 2.1 log CFU/mL at multiplicity of infection (MOI) of 100 and 10,000 respectively, as relative to the phage-excluded control. The features of phage PSDA-2 suggest that it has the potential to be an agent to control Salmonella.