In Vitro Lytic Activity and Surface Persistence of Bacteriophages and Efficacy of a Phage Cocktail Against Multidrug-Resistant Monophasic Salmonella Typhimurium on Different Poultry Farm Surfaces

Background/Objectives: Organic matter can compromise cleaning and disinfection (C&D) efficacy, making Salmonella control on farms challenging. This study aimed to characterize the in vitro lytic activity of individual bacteriophages (BPs) against mST and other Salmonella serovars of public health importance and to select BPs with complementary lytic profiles for cocktail formulation. The resulting BP cocktail was then evaluated against multidrug-resistant mST under simulated poultry farm conditions on metal, concrete, and plastic slat surfaces in the presence of organic matter, while BP persistence and viability were monitored over time. Methods: Individual BPs were screened for lytic activity against mST, SE, ST, SV, SH, and SI, and four BPs with complementary lytic profiles were selected and combined into a cocktail at 107 PFU/mL. The resulting BP cocktail was then evaluated under simulated poultry farm conditions for its ability to control mST on metal, concrete, and plastic slats. The surfaces were then contaminated with poultry faeces artificially inoculated with mST at 106 CFU/g and treated with two applications of the BP cocktail at a 24 h interval. Salmonella detection and BP persistence on the different surfaces were monitored throughout the experiment. Results: Following the first BP application, Salmonella detection was significantly reduced, with no Salmonella detected on metal surfaces. After the second application, Salmonella was no longer detected on any of the treated surfaces. In addition, the BP cocktail persisted on all surfaces, maintaining a titre of 5.14 log10 PFU/mL at the end of the experimental period. Conclusions: The selected BP cocktail demonstrated lytic activity against six epidemiologically important Salmonella serovars and reduced multidrug-resistant mST on faeces-contaminated poultry surfaces after two applications. These results support its potential use as a complementary biosanitation strategy for C&D procedures.