Figure 4.

Effects of zinc and other metals on Stx production from STEC, and on recA expression. Panels A and B, effect of metals on production of Stx2 from STEC strain Popeye-1. In both panels, the results of 3 separate experiments are combined and expressed as a percent compared to the amount of Stx2 in the presence of 4 ng/mL ciprofloxacin alone (mean ± SD). *significantly reduced compared to the no-zinc control, by ANOVA. Panels C-H, expression of recA as measured in the Miller assay using reporter strain JLM281 (recA-lacZ). Panel C, effect of hypoxanthine ± XO on recA expression. Despite the lack of asterisks, recA expression was significantly higher in the presence of XO than in its absence for concentrations of hypoxanthine of 0.8 mM or higher. Panel D, H₂O₂ induction of recA expression in JLM281. Panel E, reversal of ciprofloxacin-induced recA expression by zinc. Panels F-H, comparison of other metals on recA expression, with results normalized as a ratio to that of the “plus ciprofloxacin, no metal” condition for each metal and concentration.