AbstractShigella flexneri is the leading cause of bacillary dysentery (bloody diarrhea) with 165 million cases per yearworldwide, including 1 million deaths. There is no vaccine currently available and the isolation of multipleantibiotic resistant strains from patients worldwide is becoming the norm. S. flexneri pathogenesis relies on thecolonization of the human colon where the pathogen invades epithelial cells and spreads directly from cell tocell through actin-based motility. Using an infant rabbit model of human shigellosis recently developed by ourgroup, we have discovered that the severity of the symptoms observed during bacillary dysentery, includingbloody diarrhea and destruction of the intestinal mucosa, correlates with the efficiency of S. flexneridissemination through cell-to-cell spread. Targeting the cellular pathways supporting S. flexneri disseminationtherefore represents a potential medical countermeasure for bacillary dysentery. Here, we propose to discoversmall molecules that inhibit S. flexneri dissemination (Aim 1) and to prioritize the hit set based on chemical andbiological triage (Aim 2) and limited and exploratory medicinal chemistry (Aim 3).