Dysbiosis and intestinal inflammation caused by Salmonella Typhimurium in mice can be alleviated by preadministration of a lytic phage

Many studies have shown the efficacy of phage therapy in reducing intestinal pathogens. However, phage-based probiotic treatment is poorly studied in view of effects on the gut microbiota and intestinal inflammation. In this study, a lytic or a temperate phage (each at 4 ×10⁸ PFU per day) or a streptomycin solution (40 mg per day) were administered to mice via drinking water for 31 days. Subsequently, mice were challenged with Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium). S. Typhimurium does not serve as the host bacterium and is not lysed by both phages. For intestinal inflammation evaluation, mice were given one dose of streptomycin for 24 h before the S. Typhimurium challenge. High-throughput sequencing analysis revealed that the phylum Firmicutes became the most abundant in mice pretreated with phages. The alpha diversity of gut bacteria was higher in phage treated than in streptomycin treated mice. Moreover, pretreatment with the lytic and the temperate phage before the S. Typhimurium challenge increased two beneficial genera, Lactobacillus and Bifidobacterium. According to the pathological analysis of ileum, cecum, and serum, temperate or lytic gut phage pretreatment of mice markedly reduced intestinal inflammation, concomitant with lower serum concentration of lipopolysaccharides (LPS) and diamine oxidase (DAO). The oral pretreatments of mice (ST, Lyt, Lys, SM) generally caused an increased expression of IL-1β, TNF-α, IFN-γ, IL-4, and IL-10 compared to the matching control. However, in mice pretreated with the lytic phage, the mRNA expression for the pro-inflammatory cytokine TNF-α was not significantly higher than that of the control group. No significant differences were detected for peripheral blood B lymphocytes, CD3 +T cells, and the CD4 + /CD8 + ratio in mice pretreated with the lytic and lysogenic phage. This study demonstrated that even lytic phages not targeting the pathogenic serovar Salmonella Typhimurium alleviated intestinal dysbiosis and inflammation in challenged mice.