The image shows two cultured human liver cells infected with Shigella, the causative agent of Bacillary Dysentery. The bacterium is able to polymerise host cell actin ( fibre like proteins that contribute to cell structure and motility ) to move around in the cell. Moving bacterium shown in blue with an actin tail in red. Occasionally, the bacterium punches through the cell membrane to form protrusions and it is by this route that it will spread to adjacent cells. The large blue elliptical discs are the nuclei of the human cells, the small blue rod shaped structures are the bacteria.
Shigella causes bacillary dysentery by invading gut epithelium. Actin-based intracellular motility is one of the primary virulence properties, which aids the dissemination of the bacteria in the large intestine and rectum. Figure shows polymerised actin tail at one pole of a moving bacterium in the cell. Actin polymerisation is also the basis for the bacteria to form protrusions which allow Shigella spread from cell-to-cell.