Stress conditions stimulate overexpression of visP in diarrheagenic E. coli strains. (A and B) qRT-PCR of visP from feces collected from days 1 to 10 p.i. of both C227-11 (Stx+) and BA3826 (Stx–) strains after treatment with LED209. (C and D) qRT-PCR of visP from RNA collected from cultures of WT C227-11 (Stx+), ::qseC, qseC+, BA3826 (Stx–), 042 and EHEC 86-24 strains after 1 h of static incubation at 37°C in pH 7.2 (C) and 3.0 (D). A Student t test was employed to determine statistical significance between treated and nontreated groups or ANOVA comparing to WT C227-11 (Stx+) strain. Error bars indicate the SD of the mean (*, P < 0.01; **, P < 0.001; ***, P < 0.0001; ns, not significant).