SMART design of a Multi-receptor Phage Cocktail to tackle Salmonella in Poultry

Introduction: Salmonella is the most prevalent food-borne bacterial pathogen around the world causing gastroenteritis in humans with high incidence in poultry products. This has been linked to contamination during processing and the failure of current antimicrobial interventions. Bacteriophages (phages) are viruses that specifically infect and kill bacteria. For this reason, their use as antimicrobials has been proposed in different settings including food safety.
Purpose: The purpose of this study is to evaluate the efficacy of a multi-receptor phage cocktail to control the growth of Salmonella in vitro and in chicken skin.
Methods: Five fully characterized phages were selected for cocktail composition. This cocktail targets four different receptors: O-antigen, BtuB, OmpC, and rough Salmonella strains. A total of 66 Salmonella strains (comprising 22 serovars) were challenged with different cocktail concentrations for 24 hours in liquid culture at 25°C to evaluate growth inhibition. Salmonella Enteritidis was used to study growth inhibition at 25°C and 15°C for 48 and 96 hours, respectively, and the development of resistance. Furthermore, the cocktail treatment was evaluated in a biocontrol experiment. Chicken skin pieces of 1 cm2 were dipped into cocktail suspension containing either 5 or 7 log10 PFU/mL and incubated at three temperatures (25, 15, and 4°C). The bacterial reduction was evaluated overtime for 48 hours by platting on XLT-4 plates.
Results: Treatment with the phage cocktail in vitro at MOI of 103 significantly inhibited the growth of all Salmonella strains tested. Bacteria challenge experiments using S. Enteritidis treated with different phage concentrations (MOIs 10-1-103) showed complete growth inhibition at 25°C and 15°C for 48 and 96 hours, respectively. No cross-resistance to all phages in the cocktail was observed. Biocontrol experiments showed a 3.5 log10 CFU/cm2 reduction after 48 hours with treatments of 7 log10 PFU/mL at 25 and 15°C, and 2.5 log10 CFU/cm2 at 4°C.
Significance: These results suggest that this bacteriophage cocktail is a promising biocontrol tool against Salmonella that can be applied during poultry processing to enhance food safety.