Optimizing phage therapy for Salmonella Pullorum: dosage, timing, and pharmacokinetics define treatment efficacy in SPF chickens.

Phage therapy has emerged as a highly effective antibiotic alternative for treating Salmonella infections; however, research into how phage dosage, administration timing, and frequency influence therapeutic efficacy-along with phage pharmacokinetics-remains limited. In this study, we established a Salmonella Pullorum infection model in specific-pathogen-free (SPF) chickens to investigate these parameters, alongside the therapeutic efficacy and pharmacokinetic distribution of the phage. The study consisted of two sequential experiments: trial 1 systematically evaluated the effects of phage dosage, administration timing, and frequency on treatment outcomes, leading to the identification of an optimal dosing regimen. This optimized regimen was then applied in trial 2, which focused on characterizing the pharmacodynamic and pharmacokinetic profiles of phage vB_SalS_JNS02 in SPF chickens. The results demonstrated that phage dosage, administration timing, and frequency significantly influenced survival rates: prophylactic administration was more effective than delayed treatment, and notably, higher doses did not consistently yield superior outcomes when administered at the same time point. Phage treatment effectively reduced Salmonella colonization in the blood, tissues, and intestines, achieving complete clearance of the pathogen from the brain and blood within 2-3 days post-challenge, and from the heart and ileum by day 5. Furthermore, phage therapy restored intestinal morphological parameters-including villus height and crypt depth-to levels comparable with those of uninfected controls, while simultaneously mitigating Salmonella-induced histopathological damage and promoting tissue repair. Interestingly, although phage administration altered the composition and abundance of specific gut microbiota taxa, it exerted no significant impact on alpha diversity. Pharmacokinetic analysis revealed that orally administered phages rapidly entered the systemic circulation and tissues, reaching peak concentrations at 4 hours post-administration. Phages were completely cleared from the blood by day 5 but remained detectable in the lungs, kidneys, spleen, and liver until the final observation time point (day 9). Collectively, these findings indicate that phage JNS02 exhibits favorable pharmacokinetic and pharmacodynamics properties, positioning it as a promising antibiotic alternative and a candidate for clinical use in treating Salmonella infections.