Regulation and temporal expression patterns of Vibrio cholerae virulence genes during infection

The temporal expression patterns of the critical Vibrio cholerae virulence genes, tcpA and ctxA, were determined during infection using a recombinase reporter. TcpA was induced biphasically in two temporally and spatially sep arable events in the small intestine, whereas ctxA was induced monophasical ly only after, and remarkably, dependent upon, tcpA expression; however, th is dependence was not observed during in vitro growth. The requirements of the virulence regulators, ToxR, TcpP, and ToxT, for expression of tcpA and ctxA were determined and were found to differ significantly during infectio n versus during growth in vitro. These results illustrate the importance of examining virulence gene expression in the context of bona fide host-patho gen interactions.