Shigella bacteria on intestinal tissue. Fluorescence light micrograph of human intestinal cells infected with Shigella bacteria (small blue dots), a common cause of dysentery. The intestinal cell nuclei are stained red, while the cytoskeleton of the cells is stained green. Once released into the cytoplasm of the cells, the bacteria multiply and nucleate host cell actin (green) on one end. This hijacking of cellular protein confers motility to the bacteria and can be observed as a characteristic 'comet tail' (one example seen at lower left).