Isolation and Characterization of Two Lytic Bacteriophages Infecting a Multi-Drug Resistant Salmonella Typhimurium and Their Efficacy to Combat Salmonellosis in Ready-to-Use Foods.

Foodborne salmonellosis is a global threat to public health. In the current study, we describe the isolation and characterization of two broad-spectrum, lytic Salmonella phages: SPHG1 and SPHG3 infecting a multidrug-resistant Salmonella Typhimurium EG.SmT3. Electron microscopy and whole genome analysis identified SPHG1 as a Myovirus, while SPHG3 as a new member of the genus "Kuttervirus" within the family Ackermannviridae. SPHG1 and SPHG3 had a lysis time of 60 min. with burst sizes of 104 and 138 PFU/cell, respectively. The two phages were robust at variable temperatures and pH ranges that match the corresponding values of most of the food storage and processing conditions. A phage cocktail containing the two phages was stable in the tested food articles for up to 48 h. The application of the phage cocktail at MOIs of 1000 or 100 resulted in a significant reduction in the viable count of S. Typhimurium by 4.2 log10/sample in milk, water, and on chicken breast. Additionally, the phage cocktail showed a prospective ability to eradicate and reduce the biofilm that formed by S. Typhimurium EG.SmT3. A phage cocktail of SPHG1 and SPHG3 is considered as a promising candidate as a biocontrol agent against foodborne salmonellosis due to its broad host ranges, highly lytic activities, and the absence of any virulence or lysogeny-related genes in their genomes.