Cholera remains a devastating bacterial cause of human morbidity and mortality in developing countries. The diseases is produced by a gram-negative, motile Vibrio cholerae that colonizes in the human intestine and secretes a potent cholera toxin, which ultimately stimulates cellular adenylate cyclase to cause massive intestinal fluid loss leading to profuse watery diarrhea. Live-attenuated V. cholerae vaccines harboring deletions of cholera toxin have great promise for reducing the global burden of cholera. However, development of live vaccines has been hampered by the tendency of such...