The bacteria Enteropathogenic E. coli (EPEC) is a major cause of infantile diarrhea, killing an estimated 100,000 children every year. (The bacteria is also closely related to enterohemorrhagic E. coli 0157:H7, which causes hamburger disease.) Most bacteria attach to existing proteins on host cells to cause disease. EPEC inserts its own protein into host cells and then attaches itself to the protein. Annick Gauthier is studying a specialized transport system—called a type III secretion system—that is believed to deliver this necessary protein from the EPEC bacteria into host cells. Her goal is to understand this fundamental mechanism, which is found only in disease-causing bacteria. Learning how this system works could provide targets for both vaccine and antibiotic development that would harm only the disease causing E. coli, and not the healthy bacteria that normally reside in the intestine.