MOLECULAR AND CELLULAR BASES OF EPITHELIAL-CELL INVASION BY SHIGELLA-FLEXNERI

A key step in the pathogenesis of shigellosis is the capacity of the c ausative bacteria, shigellae, to invade colonic and rectal epithelial cells in humans. This invasive process encompasses several steps: entr y into epithelial cells by induction of a macropinocytic event caused by secreted Ipa proteins. The bacterium then escapes from the vacuole and reaches the cytoplasmic compartment in which it divides rapidly an d becomes motile via the expression of a surface protein, IcsA, whose polar localization achieves directed polymerization of actin filaments that push the bacterial body forward. Bacteria then engage the inner face of the cellular membrane in the junctional area and form protrusi ons allowing their passage into the adjacent cell. Lysis of the double membrane eventually allows access to the cytoplasmic compartment of t he adjacent cell, thus providing the bacterium with a very efficient m echanism of epithelial colonization.