The protective effect of dietary supplementation of Salmonella-specific bacteriophages in post-weaning piglets challenged with Salmonella typhimurium

Objective: The efficacy of Salmonella typhimurium-specific bacteriophage STP-1 on S. typhimurium infection in weaning piglets was evaluated in this study.  Material and Methods: Twenty-eight weaning piglets were randomly allocated to four groups (Group A: non-challenged/basal; Group B: non-challenged/+phage; Group C: challenged/basal; Group D: challenged/+phage) according to S. typhimurium infection or bacteriophage administra­tion. The total experimental period (14 days) was subdivided in to non-challenged periods (phase I; day 1–7) and challenged periods (phase II; day 7–14) based on the challenging date (day 7). Each group was fed with basal feed or feed supplemented with bacteriophage STP-1 [1.0 × 109 plaque-forming unit (PFU)/kg] during the whole period (day 1–14). Body weights (BW) were mea­sured to evaluate growth performance. Clinical symptoms (rectal temperatures and fecal consis­tency) induced by S. typhimurium were regularly checked. Bacteria colonization levels in feces and intestinal tissue samples were measured using real-time polymerase chain reaction (PCR). After necropsy, small intestine samples (jejunum) were collected. Villus height and crypt depth (CD) were measured through histological examination with H&E staining.  Results: The supplementation of bacteriophage significantly reduced bacterial colonization and intestine damage in the piglets infected with S. typhimurium. In the antigen concentrations of the feces and jejunum, Group C showed 5.8 ± 0.6, 5.7 ± 0.6, and 1.2 ± 2.0 log colony-forming unit (CFU)/ml on 1, 3, and 7 days post-inoculation (DPI) and 2.8 ± 1.3 log CFU/ml, whereas Group D showed 3.5 ± 1.7, 2.2 ± 2.1, and 0.3 ± 0.9 log CFU/ml on 1, 3, and 7 DPI and 5.1 ± 0.9 log CFU/ml. In the villous height, Groups C and D showed 266.3 ± 24.1 and 324.6 ± 18.0 μm, respectively. In the goblet cell density of villi and crypts, Group C showed 10.0 ± 1.8 and 16.0 ± 3.7, while Group D showed 15.0 ± 4.8 and 21.1 ± 5.4. Also, the supplementation of bacteriophage significantly improved the growth performance in the infected piglets. The average daily gains of Groups C and D were 91 ± 24 and 143 ± 23, respectively, during the period after inoculation with S. typhimurium.  Conclusion: The dietary supplementation of the phage was effective for alleviating S. typhimurium infection in post-weaning piglets. J. Adv. Vet. Anim. Res., 8(2): 440-447, June 2021 http://doi.org/10.5455/javar.2021.h532