Impact of hydroxyl- and superoxide anion-based oxidative stress on logarithmic and stationary phase Escherichia coli O157:H7 stress and virulence gene expression.

Targeted microarray analysis was used to examine growth phase-related transcriptional responses of Escherichia coli O157:H7 stress and virulence genes. Logarithmic and stationary phase cells were exposed to hydrogen peroxide (H(2)O(2); 1 and 2.5 mM) and paraquat (PQ; 350 μM) for 40 min. For both oxidants, more genes were significantly induced in logarithmic cells compared to cells in stationary phase. In total, 14 genes at 1 mM H(2)O(2) and 15 genes at 2.5 mM H(2)O(2) were significantly induced in logarithmic cells, with 11 affected genes common between treatments, including stx2a and stx2b. At 2.5 mM H(2)O(2), additional virulence genes were induced, including stx1a, stx1b, lpfA, a putative enterotoxin, and ler. Stx2 ELISA showed transcriptional induction of stx2a and stx2b correlated with significantly increased Stx2 in cultures exposed to 1 and 2.5 mM H(2)O(2). Logarithmic cells significantly induced 15 genes following PQ exposure, 12 of which were induced in H(2)O(2)-treated cells, including several virulence genes (stx1a, stx2a, and stx2b). Exposure of stationary phase cells to H(2)O(2) and PQ had little effect on the queried transcriptome, demonstrating the importance of considering this inherently stress resistant state when evaluating food safety interventions.