Impact of a defined bacterial community including and excluding Megamonas hypermegale on broiler cecal microbiota and resistance to Salmonella infection

Abstract Intensive broiler production practices impair the transmission of commensal microbes from hens to offspring, resulting in a lower abundance of non-spore-forming strict anaerobic bacteria. We evaluated the effects of colonization by a defined community (DC) of bacteria including and excluding Megamonas hypermegale in chicks challenged with Salmonella . Inoculation with DC resulted in higher phylogenetic diversity and the dominance of Bacteroidetes species in the cecal microbiota, with a decrease in the relative abundance of Salmonella and Escherichia/Shigella , as well as a lower Enterobacteriaceae load. Substantial shifts in microbiota composition were coupled with subtle changes in metabolites and host responses, including changes in interferon-γ, macrophage colony-stimulating factor, propionate, valerate, and isovalerate concentrations in the ceca. We identified bacterial species that were able to establish and persist after a single exposure, many of which were members of Bacteroidetes. Although co-culture with M. hypermegale reduced Salmonella counts by 99.3% in vitro , in vivo inoculation of M. hypermegale increased splenic Salmonella counts in inoculated chicks. The use of DC containing bacteria isolates harvested from the cecal contents of mature chickens can recapitulate the changes in volatile fatty acid concentrations observed in birds colonized with complex communities, and the presence of M. hypermegale specifically enhances the production of propionate. Our findings suggest that the use of DC can be explored as a strategy to control disease occurrence in broiler production; however, further research is warranted to properly understand the role of individual species in the broiler cecal community aiding the formulation of appropriate DCs. Importance Intensive production practices can reduce beneficial gut bacteria in broiler chickens, potentially leading to higher disease risk. We investigated whether introducing a defined community (DC) of beneficial bacteria, along with M. hypermegale , could improve gut health and resistance to Salmonella in broiler chicks. Our findings show that DC increases microbial diversity and reduces the relative abundance of potential pathogens, like Salmonella and Escherichia/Shigella , which was coupled with subtle changes in the immune responses of the birds and higher concentration of volatile fatty acids in the ceca. This study suggests that using DC can enhance poultry health and reduce disease, providing a potential strategy to improve broiler production. However, further research is needed to understand the roles of individual bacteria and refine these bacterial communities for practical use in farming. This work holds promise for developing natural methods to enhance poultry health and safety.