Inflammatory responses induced by the monophasic variant of Salmonella typhimurium in pigs play a role in the high shedder phenotype and fecal microbiota composition

<p>Pigs infected with <em><span>Salmonella</span></em> may excrete large amounts of <em><span>Salmonella</span></em>, increasing the risk of spread of this pathogen in the food chain. Identifying <em><span>Salmonella</span></em> high shedder pigs is therefore required to mitigate this risk. We analyzed immune-associated markers and composition of the gut microbiota in specific-pathogen-free pigs presenting different shedding levels after an oral infection with <span>Salmonella</span>. Immune response was studied through total blood cell counts, production of anti-<em><span>Salmonella</span></em> antibodies and cytokines, and gene expression quantification. Total <em><span>Salmonella</span></em> shedding for each pig was estimated and hierarchical clustering was used to cluster pigs into high, intermediate, and low shedders. Gut microbiota compositions were assessed using 16S rRNA microbial community profiling. Comparisons were made between control and inoculated pigs, then between high and low shedders pigs. Prior to infection, high shedders had similar immunological profiles compared to low shedders. As soon as 1 day postinoculation (dpi), significant differences in the cytokine production level and on the expression level of several host genes related to a proinflammatory response were observed between high and low shedders. Infection with <em><span>Salmonella</span></em> induced an early and profound remodeling of the immune response in all pigs, but the intensity of the response was stronger in high shedders. In contrast, low shedders seroconverted earlier than high shedders. Just after induction of the proinflammatory response (at 2 dpi), some taxa of the fecal microbiota were specific to the shedding phenotypes. This was related to the enrichment of several functional pathways related to anaerobic respiration in high shedders. In conclusion, our data show that the immune response to <em><span>Salmonella</span></em> modifies the fecal microbiota and subsequently could be responsible for shedding phenotypes. Influencing the gut microbiota and reducing intestinal inflammation could be a strategy for preventing <em><span>Salmonella</span></em> high shedding in livestock.</p>