The duodenal microbiome in health and disease: composition and dynamics in relation to the bile salt pool, mucosal physiology and therapy in functional and inflammatory disorders of the duodenum.

FD is a common disorder with unknown pathophysiology, hampering a conclusive diagnosis and development of effective drugs. In this PhD-project, we studied duodenal and systemic factors in FD. We focused on the duodenal lumen and mucosa, as luminal changes have been proposed to initiate or maintain mucosal alterations. We also separated the duodenal luminal and mucosa-associated microbiota composition. Effects of first-line therapy or PPI were prospectively studied in FD patients compared to controls and a second cohort of PPI-refractory FD patients after PPI-withdrawal. Finally, the clinical efficacy and underlying immune and microbial mechanisms of spore-forming probiotics were studied in FD patients on- or off-PPI, which is relevant regarding the potential cumulative effect of PPI and spore-forming probiotics on luminal and systemic changes in FD.