The amplification of bacteriophages using Salmonella YB1 as a host and its therapeutic efficacy against salmonellosis in broilers.

The residual bacteria in bacteriophage (phage) preparations have hindered their application in poultry disease. We isolated eight phages from aquatic environment samples and selected two phages (vB_StyS_SP03 and vB_StyM_SP07) for amplification using the diaminopimelic acid (DAP)-dependent Salmonella YB1 strain. Both healthy and Salmonella-infected broilers were intraperitoneally injected with phages amplified by Salmonella YB1 and their cocktail to evaluate the safety and therapeutic efficacy. The results showed that Salmonella YB1 effectively amplified phages, whose form and function remained unchanged after amplification. Salmonella YB1 in the phage preparations did not proliferate without DAP supplementation. Phage administration caused no mortality, and did not significantly affect the weight gain, immune organ indexes, and gut microbiota composition in healthy broilers. In Salmonella-challenged broilers, phage administration significantly improved weight gain, reduced organ indexes, alleviated clinical symptoms and pathological changes, and restored the intestinal microbial community. Collectively, we have developed a method for amplifying phages using Salmonella YB1, which effectively addresses the problem of residual bacteria in phage preparations.