Organic compounds showing the ability to inhibit effector toxin secretion or translocation mediated by bacterial type III secretion systems are disclosed. The disclosed type III secretion system inhibitor compounds are useful for combating infections by Gram-negative bacteria such as Salmonella spp., Shigella flexneri, Psendomonas spp., Yersinia spp., en tero pathogenic and enteroinvasive Escherichia coli, and Chlamydia spp. having such type III secretion systems.