Alginate encapsulation enhanced the gastrointestinal stability and bactericidal efficacy of an optimized Salmonella phage cocktail for oral delivery in poultry feed

Salmonella is a leading cause of gastroenteritis, and it is transmitted via contaminated water and food sources, especially poultry products. Many serovars are resistant to frontline antibiotics, necessitating the need for alternative treatment strategies. Bacteriophage (phage) therapy offers a promising alternative to antibiotics for Salmonella infection control in poultry, however, oral delivery is limited by the highly acidic gastric environment. Thus, this study aimed to optimize a cocktail of encapsulated phages to preserve and enhance their shelf-life, viability, target release and activity in the digestive tract of chickens. The phage cocktail, consisting of three strictly lytic Salmonella phages (ST-W23, SE-W112, and ST-W139) isolated from wastewater, exhibited a broad host range, lysing ∼83 % (107/129) of 25 important Salmonella serovars identified from chicken farms. To enhance stability in acidic conditions, the phage cocktail was encapsulated in alginate-CaCO₃ jelly beads. Under simulated gastric conditions, a single application of the encapsulated cocktail reduced S. Typhimurium growth below detectable limits within 3 h post-treatment and inhibited further regrowth for 24 h. Furthermore, the encapsulated phages maintained high viability for at least a month at room temperature, eliminating the need for cold storage logistics. This study demonstrates an effective phage encapsulation technique for optimal phage storage, oral administration and therapeutic efficacy to control intestinal Salmonella in poultry and protect public health. Further work will focus on upscaling phage production and testing in poultry farms.