Influence of polyphenols on Escherichia coli resistance to oxidative stress

Among all polyphenols tested (tannic acid and flavonoids belonging to different subclasses) only tannin and quercetin significantly enhanced resistance of Escherichia coli to peroxide stress. Pretreatment of the cells with quercetin and tannin resulted in a decrease in the growth arrest duration under moderate H2O2 concentration (2 mM) and an increase in survival under high (10 mM) doses. The shorter growth recovery period in pretreated cells was connected with more rapid H2O2 elimination because of induced activity of scavenging enzymes. This effect was absent in the ΔoxyR mutant, which was unable to induce genes responding to peroxide stress. The data obtained suggest that the observed protection was a result of two overlapping effects: induction of OxyR regulon by low concentrations of H2O2, accumulated during extracellular autoxidation of quercetin and tannin, and protection of synthesis of OxyR-regulated antioxidant enzymes during H2O2 stress because of intracellular binding of iron by quercetin and tannin and suppressing Fenton chemistry.