Fig 1.

Virulence gene expression in V. cholerae adhered to INT 407 cells. RNA was extracted from INT 407-adhered V. cholerae at different times after adherence for estimation of ctxAB and tcpA expression by qRT-PCR. As a control experiment (labeled unadhered), ctxAB and tcpA gene expression was estimated in V. cholerae incubated under identical conditions without a cell line. The expression of each gene was normalized to that of the internal reference, the 16S rRNA gene. Relative expression levels were calculated as the expression of a gene divided by that in unadhered V. cholerae at the beginning of the experiment (0 h), which was arbitrarily defined as 1. Data presented are averages of five independent experiments, and error bars represent standard deviations. The significance of differences in the expression of the ctxAB or tcpA genes in unadhered and adhered V. cholerae cells was determined by Student's t test and is indicated as follows: **, P < 0.01; *, P < 0.05.