PROJECT SUMMARY/ABSTRACT Shigella flexneri is a human pathogen that causes shigellosis, a severe diarrheal disease. S. flexneri invades the colonic mucosa where it replicates in the cytosol of epithelial cells and spreads from cell to cell. This dissemination process relies on cytosolic actin-based motility and formation of membrane protrusions that project into adjacent cells. The resolution of these membrane protrusions leads to formation of double membrane vacuoles (DMVs), from which the bacteria subsequently escape, thereby gaining access to the cytosolic compartment of adjacent cells. Our lab has shown that the S. flexneri type three secretion system (T3SS) is required at multiple stages of the dissemination process, including protrusion resolution and double membrane DMV escape. I have shown recently that the T3SS effector protein IcsB contributes to S. flexneri dissemination by promoting prompt and efficient escape from DMVs. Here, I propose to determine the mechanism by which IcsB facilitates DMV escape (Aim 1) and its relevance to pathogenesis in our recently developed infant rabbit model of human shigellosis (Aim 2). My central hypothesis is that IcsB is a critical virulence factor that manipulates host Rho GTPases to promote prompt and efficient DMV escape. Since S. flexneri dissemination is a critical determinant of pathogenesis, my work may reveal novel therapeutic intervention for treating human shigellosis.

PROJECT NARRATIVE Bacillary dysentery, a worldwide diarrheal disease caused by Shigella flexneri, causes an estimated 165 million cases and over 1 million deaths annually. Lack of an effective vaccine and the emergence of multi-drug resistant S. flexneri strains heighten the necessity for novel therapeutic approaches. I am proposing to study a specific mechanism that allows S. flexneri to disseminate and cause disease, which could potentially lead to the identification of novel avenues for therapeutic intervention. ! !