Shigella bacteria wreak their havoc by invading, multiplying and killing the cells that line the colonic mucosa. Once the bacteria are inside host cells they can trigger them to produce pro-inflammatory mediators such as interleukin 8. This helps to create a strong inflammatory response that eases the way for further bacterial invasion.
Several virulence factor genes have been indentified such as; -
icsA gene - codes for an outer membrane protein that allows the bacteria to move easily through the cytoplasm
shet2 gene - codes for an enterotoxin
Shigella bacteria adhere to host cells and more than 25 genes are involved in helping to get them across the membrane. Shigella is surrounded by a membrane-bound vacuole within the host cell which it rapidly lyses. The bacteria is then released into the cytosol where it rapidly grows and divides.
Once released the bacteria are coated in filamentous actin which forms a tail at one pole to drive the bacteria toward the plasma membrane. Once there they forms projections from the surface of the infected cell to the surface of an unaffected cell. A tip penetrates the latter and the bacteria eventually break out of the infected cell to colonise a new cell.
Some strains produce Shiga toxin and enterotoxin that have cytotoxic effects and can cause a range of problems including hemolytic uremic syndrome. This can lead to a loss of kidney function.