A Combination of Virulent and Non-Productive Phages Synergizes the Immune System against Salmonella Typhimurium Systemic Infection

Abstract

Effective phage cocktails consisting of multiple virus types are essential for successful phage therapy against pandrug-resistant pathogens, including Salmonella enterica serovar (S.) Typhimurium. Here we show that a Salmonella phage, F118P13, with non-productive infection and a lytic phage, PLL1, combined to inhibit pandrug-resistant S. Typhimurium growth and significantly limited resistance to phages in vitro. Further, intraperitoneal injection with this unique phage combination completely protected mice from Salmonella-induced death and inhibited bacterial proliferation rapidly in various organs. Furthermore, the phage combination treatment significantly attenuated the inflammatory response, restored the generation of CD4+ T cells repressed by Salmonella, and allowed macrophages and granulocytes to participate in immunophage synergy to promote bacterial clearance. Crucially, the non-productive phage F118P13 is less likely to be cleared by the immune system in vivo, thus providing an alternative to phage cocktail against bacterial infections.

Research Note: Therapeutic effect of a Salmonella phage combination on chicks infected with Salmonella Typhimurium

“…By further testing the load of Salmonella in various organs of infected chicks, we found that phage treatment greatly reduced the bacterial load in various organs, and the decrease of the number of Salmonella in the spleen and bursa was significantly greater than that in the liver and cecal contents, which may be due to higher phage titers in immune organs ( Figure 1F ). The result that phages tend to reside in immune organs was also observed previously in a mouse model treated with this phage combination, in which the titer and residence time of phage in spleen and thymus of mice were significantly higher than those in liver and kidney ( Liang et al, 2022 ). The time of bacteriophage persistence and their concentration in a particular organ strongly depends on the absence or presence of susceptible bacteria in an animal's body ( Dabrowska et al, 2005 ).…”

“…We previously demonstrated that a combination containing virulent and nonproductive phages could not only inhibit pandrug-resistant S . Typhimurium growth and the emergence of phage resistance in vitro, but also protected mice from Salmonella -induced death with the help of immune system ( Liang et al, 2022 ) . In the current study, we further explored the effect of this phage combination in a SPF chick model.…”

“…The phage combination contains Salmonella virulent phage PLL1 (GenBank accession OM367911) and nonproductive phage F118P13 (GenBank accession OM339548), and 2 phages could produce different clear plaques on S . Enteritidis SE3377 ( Liang et al, 2022 ). Phage mixtures were prepared by mixing 2 phages at a ratio of 1:1, with each phage at a titer of approximately 0.5 × 10 9 PFU/mL, later diluted 10-fold in sterile SM buffer to ∼10 8 PFU/mL for use.…”

“…In addition, the phage combination protected mice from S . Typhimurium-induced death with the help of host's immune system by inhibiting the rapid proliferation and spread of bacteria in various organs and attenuating the inflammatory response in a mouse model ( Liang et al, 2022 ). Here, we aim to further explore therapeutic effect of this phage combination in chicks infected with pandrug-resistant S .…”