title: Increasing the oxidative stress response allows Escherichia coli to overcome inhibitory effects of condensed tannins.
abstract: Tannins are plant-derived polyphenols with antimicrobial effects. The mechanism of tannin toxicity towards Escherichia coli was determined by using an extract from Acacia mearnsii (Black wattle) as a source of condensed tannins (proanthocyanidins). E. coli growth was inhibited by tannins only when tannins were exposed to oxygen. Tannins auto-oxidize, and substantial hydrogen peroxide was generated when they were added to aerobic media. The addition of exogenous catalase permitted growth in tannin medium. E. coli mutants that lacked HPI, the major catalase, were especially sensitive to tannins, while oxyR mutants that constitutively overexpress antioxidant enzymes were resistant. A tannin-resistant mutant was isolated in which a promoter-region point mutation increased the level of HPI by 10-fold. Our results indicate that wattle condensed tannins are toxic to E. coli in aerobic medium primarily because they generate H(2)O(2). The oxidative stress response helps E. coli strains to overcome their inhibitory effect.
authors.affiliation: Department of Animal Sciences, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Alexandra H
authors.initials: AH
authors.lastname: Smith
authors.forename: James A
authors.initials: JA
authors.lastname: Imlay
authors.forename: Roderick I
authors.initials: RI
authors.lastname: Mackie
mesh_terms: D000045:Acacia / Q000737:chemistry; D000332:Aerobiosis; D000693:Anaerobiosis; D000872:Anthocyanins / Q000378:metabolism / Q000494:pharmacology*; D001483:Base Sequence; D002374:Catalase / Q000235:genetics; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D018869:Heat-Shock Response; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010936:Plant Extracts / Q000494:pharmacology; D044945:Proanthocyanidins; D017422:Sequence Analysis, DNA
chemical_list: D000872:Anthocyanins; D029968:Escherichia coli Proteins; D010936:Plant Extracts; D044945:Proanthocyanidins; C013221:proanthocyanidin; D002374:Catalase; C051253:katG protein, E coli