Fig. 1.

Differing mechanisms by which conjugated bile acids inhibit bacterial overgrowth of the human small intestine. In the proximal small intestine (duodenum and jejunum), conjugated bile acids (and accompanying fatty acids) inhibit bacterial growth directly because of their pharmacological properties. In the distal small intestine, as presented in Inagaki et al. (4), conjugated bile acids interact with FXR in the ileal enterocyte by inducing genes promoting the synthesis and secretion of antimicrobial factors from the epithelium (solid line) or by initiating a cascade of events beyond the epithelial cell that can promote elimination of luminal bacteria (dashed line). Bile acid molecules are shown four orders of magnitude larger than their actual size.