Efficacy and safety of phage therapy against Salmonella enterica serovars Typhimurium and Enteritidis estimated by using a battery of in vitro tests and the Galleria mellonella animal model

In light of spreading antibiotic resistance among pathogenic bacteria, the development of novel approaches to combat such microorganisms is crucial. Salmonella enterica is pathogenic to humans, however, it can also infect poultry, being a potential foodborne pathogen when poultry-derived food is contaminated by this bacterium. Phage therapy is one of the alternative ways to treat Salmonella-infected animals while the establishment of this method and its introduction to a general practice requires detailed studies on safety and efficacy. Here, we present the results of such studies with two previously isolated and characterized bacteriophages, vB_SenM2 and vB_Sen-TO17, and four strains of S. enterica belonging to two serovars, Typhimurium and Enteritidis. We demonstrated effective reduction of bacterial cell number and cell culture density when using each phage alone, and in combination (as a cocktail). These phages were also effective in reducing bacterial biofilm. The efficacy of this in vitro phage therapy was compared to the action of known antibiotics, as was the efficiency of appearance of bacteria resistant to both these types of antibacterial agents. Safety of the use of bacteriophages was demonstrated using the LAL chromogenic test and the chicken fibroblast viability assay. Finally, the efficacy of phage therapy was assessed with the in vivo model of S. enterica-infected Galleria mellonella larvae, showing a significant improvement in the survival of the animals. In conclusion, we demonstrated high efficacy and acceptable safety profiles of phage therapy against S. enterica strains using vB_SenM-2 and vB_Sen-TO17 phages (both alone and in a cocktail). These results open a possibility for a trial with the use of poultry and these phages which might potentially allow to introduce of this method for practical use in poultry farming.