FIG 9.

Model of Shigella infection following bile exposure. As Shigella transits the small intestine, exposure to bile induces transcriptional changes, bile resistance mechanisms, and biofilm formation. In the terminal ileum, where the majority of bile is absorbed, Shigella disperses the biofilm and subsequently enters the colon. Transcriptional changes already induced in response to bile, such as increased anaerobic respiration and the induction of the osp and ipaH virulence genes, enable the bacteria to efficiently adapt to the colonic environment, attach and invade epithelial cells, and establish infection. The bacteria escape macrophages by inducing cell death, invade the basolateral pole of the colonic epithelium, and regulate interleukin-8 (IL-8) secretion to control polymorphonuclear (PMN) cell migration (3, 73–75).