A bacteriophage cocktail delivered in feed significantly reduced Salmonella colonization in challenged broiler chickens

Abstract

Nontyphoidal Salmonella spp. are a leading cause of human gastrointestinal infections and are commonly transmitted via the consumption of contaminated meat. To limit the spread of Salmonella and other food-borne pathogens in the food chain, bacteriophage (phage) therapy could be used during rearing or pre-harvest stages of animal production. This study was conducted to determine if a phage cocktail delivered in feed is capable of reducing Salmonella colonization in experimentally challenged chickens and to determine the optimal phage dose. A total of 672 broilers were divided into six treatment groups T1 (no phage diet and unchallenged); T2 (phage diet 10⁶ PFU/day); T3 (challenged group); T4 (phage diet 10⁵ PFU/day and challenged); T5 (phage diet 10⁶ PFU/day and challenged); and T6 (phage diet 10⁷ PFU/day and challenged). The liquid phage cocktail was added to mash diet with ad libitum access available throughout the study. By day 42 (the concluding day of the study), no Salmonella was detected in faecal samples collected from group T4. Salmonella was isolated from a small number of pens in groups T5 (3/16) and T6 (2/16) at ∼4 × 10² CFU/g. In comparison, Salmonella was isolated from 7/16 pens in T3 at ∼3 × 10⁴ CFU/g. Phage treatment at all three doses had a positive impact on growth performance in challenged birds with increased weight gains in comparison to challenged birds with no phage diet. We showed delivering phages via feed was effective at reducing Salmonella colonization in chickens and our study highlights phages offer a promising tool to target bacterial infections in poultry.

Keywords: Salmonella; antimicrobial resistance; phage therapy; phages; poultry.

Figure 1.

Phage titres in starter, grower, and finisher mash diets. Three technical replicates were conducted for each diet and the error bars show standard error of the mean.

Figure 2.

Boxplot shows the maximum and minimum Salmonella counts isolated from faecal samples collected from the six treatment groups. Salmonella counts in challenged group T3 were compared to challenged and phage-treated groups T4 (10⁵ PFU/day), T5 (10⁶ PFU/day), and T6 (10⁷ PFU/day). Statistical differences between treatment groups (n = 16) are displayed on the graph (*p < 0.05 and **p < 0.01).

Figure 3.

Graph shows the number of pens from which Salmonella was isolated from faecal samples over the course of the study and there were 16 pens per treatment group.

Figure 4.

Boxplot shows the maximum and minimum phage counts isolated from faecal samples collected from the six treatment groups. Phages were reisolated from all phage-treated groups: T2 bird fed phage at dose 10⁶ PFU/day; and challenged and fed the phage diet groups T4 (10⁵ PFU/day), T5 (10⁶ PFU/day), and T6 (10⁷ PFU/day).

Figure 5.

Boxplots show the (a) Salmonella and (b) phage counts isolated from caeca samples collected on SD 42, the last day of the study. Salmonella counts in challenged group T3 were compared to challenged and phage-treated groups T4 (10⁵ PFU/day), T5 (10⁶ PFU/day), and T6 (10⁷ PFU/day). Statistically differences between treatment groups are displayed on the graph (*p < 0.05).

Figure 6.

Graphs show the EOP of phages SPFM10 and SPFM14 on Salmonella colonies isolated from faecal samples collected on SD 10 (a), SD 14 (b), SD 28 (c), and SD 42 (d) over the course of the trial.