Diagram of Shigella spread in the epithelium

Schematic representation of intracellular movement and spread of Shigella in epithelium. Step 1: Soon after uptake by induced phagocytosis, the bacterium lyses the phagocytic vacuole, thereby releasing it into the host cell cytosol. Step 2: Short filaments of host cell actin (brown thick lines) then organize into a tight bundle that forms a tail several microns in length behind the bacterial body. Step 3: The bacterium uses this tail to motor both its movement through the cytosol and its passage into protrusions from the cell surface; the bacterium-containing protrusions can extend several bacterial lengths away from the cell surface, with the bacterium at the tip. Step 4: The bacterium-containing protrusion tips are endocytosed by adjacent cells, thereby transferring the bacterium into the adjacent cell. Step 5: Once endocytosed within the adjacent cell, the bacterium lyses the membranes that surround it, freeing itself into the cytosol of that cell.