An exhaustive cell-based screen coupled with an intracellular-induced lux-based reporter identified bioactive molecules that inhibit host cell infection by intracellular pathogens

This multistage, screening protocol resulted in the identification of eight non-cytotoxic compounds that efficiently inhibited the intracellular growth of the Gram-negative bacterium <i>Salmonella</i> Typhimurium in human epithelial cells by ~2.5- to 6-fold, without inhibiting <i>Salmonella</i> growth in culture. Five of these eight molecules were also effective in controlling the intracellular replication of <i>Salmonella</i> in primary mouse macrophages by 1.5- to 38-fold. Strikingly, seven hits also inhibited the intracellular growth of the Gram-positive bacterial pathogen <i>Listeria monocytogenes</i> in epithelial cells by 1.5- to 10-fold. The structure-activity relationship approach successfully identified chemical analogs of one hit with enhanced biological activity as infection inhibitors. Overall, we describe a robust HTS platform that can be adapted for screening of compound libraries against other pathogens, and suggest that the identified compounds are potential candidates for downstream development of novel drugs against intracellular bacterial infections.