Human Intestinal Enteroids as a Model System of Shigella Pathogenesis

The enteric bacterium and intracellular human pathogen Shigella causes hundreds of millions of cases of the diarrheal disease shigellosis per year worldwide. Shigella is acquired by ingestion of contaminated food or water; upon reaching the colon, the bacteria invade colonic epithelial cells, replicate intracellularly, spread to adjacent cells, and provoke an intense inflammatory response. There is no animal model that faithfully recapitulates human disease; thus, cultured cells have been used to model Shigella pathogenesis. However, the use of transformed cells in culture does not provide the same environment to the bacteria as the normal human intestinal epithelium. Recent advances in tissue culture now enable the cultivation of human intestinal enteroids (HIEs), which are derived from human intestinal stem cells, grown ex vivo, and then differentiated into "mini-intestines." Here, we demonstrate that HIEs can be used to model Shigella pathogenesis. We show that Shigella flexneri invades polarized HIE monolayers preferentially via the basolateral surface. After S. flexneri invades HIE monolayers, S. flexneri replicates within HIE cells and forms actin tails. S. flexneri also increases the expression of HIE proinflammatory signals and the amino acid transporter SLC7A5. Finally, we demonstrate that disruption of HIE tight junctions enables S. flexneri invasion via the apical surface.