A bacteriophage cocktail to prevent gut microbial dysbiosis in newborn preterm piglets is well tolerated and disseminates to lymph nodes

Necrotizing enterocolitis (NEC) is a severe gastrointestinal condition primarily affecting very preterm infants. While transfer of fecal viromes from healthy donors has shown protection against NEC in animal models, the risk of introducing pathogenic viruses is evident. Applying a defined community of bacteriophages (phages), viruses that specifically infect bacteria, might offer a safer and targeted approach to prevent gut dysbiosis and NEC development. We evaluated the effects of ten rationally selected phages in a formula-fed piglet model of NEC. Forty-five preterm piglets, delivered by caesarean section, were fed increasing volumes of formula to induce intestinal pathology. During the first two days of life, piglets received either the phage cocktail (PC), a fecal virome transfer (FVT) or sterile buffer by oral gavage. Intestinal pathology and function, hematology and clinical outcomes and phage dissemination were assessed. Lastly, the extra-intestinal immune responses were evaluated by transcriptomic analysis of the gut-draining lymph nodes. The piglets demonstrated unexpectedly mild pathology, with no marked differences between the treatment groups. Both FVT and PC recipients exhibited increased intestinal permeability and altered hematology profiles, although without overt clinical deterioration. Specific DNA signatures from the phage cocktail members were detected in the colonic content and gut-draining lymph nodes of PC recipients, indicating intestinal dissemination and short-term persistence. However, several inflammatory pathways were downregulated in gut-draining lymph nodes after FVT, which was not observed in PC recipients. Although a protective effect could not be determined due to the low baseline pathology, the phage cocktail was well tolerated in preterm newborns.