In depth characterization of oral and fecal microbiome and microbial metabolism in multiple sclerosis

Multiple sclerosis is a complex inflammatory disease of the central nervous system whose precise causes remain unknown. Gut microbiota, acting as a nutrient provider and shaping the immune system of its human host, has extensively been characterized in MS. However, involvement of the oral microbiome, and its potential interactions with immune cells remains unknown in MS. Using 16SrRNA sequencing and in silico bacterial metabolism inference tools, we were able to show oral and fecal microbiome alterations and important bacterial metabolism remodeling in MS patients, compared to healthy volunteers. Our analysis showed decreased diversity indices, decreased oral/fecal compartmentalization as well as depletion in commensal bacteria (Aggregatibacter, Streptococcus in saliva and Coprobacter, Roseburia in feces) and enrichment in potentially proinflammatory bacteria in MS patients (Leptotrichia, Fusobacterium in saliva and Enterobacteriaceae, Actinomyces in feces). Similarly, we identified altered microbial pathways and metabolites at the crossroad with human metabolism and immunological pathways (polyamine pathway, remodeling of bacterial surface antigens, nitrogen and nucleoside production). Finally, we identified a specific metabolite signature in the oral compartment of the MS patients allowing us to create and validate a discrimination model. Further exploration of the interaction between oral microbiota and immunity are needed as the oral compartment appears to be an important site of immune regulation.