CEMIS-Oulu, Kajaani University Consortium, University of Oulu, Sotkamo, Finland.
Planta Med. 2012 Nov;78(17):1824-30. doi: 10.1055/s-0032-1315388. Epub 2012 Oct 11.
Quercetin is a natural flavonoid possessing a number of health beneficial effects. Its bioactivity is restricted by low solubility and sensitivity to oxidative degradation, factors that are often ignored in laboratory studies. We studied the antimicrobial effects of quercetin on Staphylococcus aureus, Escherichia coli and Lactobacillus plantarum at concentrations at which it is soluble and investigated how the antioxidant vitamin C modulates these activities. S. aureus was the most sensitive of the studied bacteria. After 12 hours of culturing, 90 µM quercetin decreased the growth of S. aureus to 75 % of the value for a control culture. 1 mM vitamin C combined with 90 µM quercetin diminished the growth of S. aureus drastically to 3 % of that of the control culture supplemented with vitamin C only. Interestingly, vitamin C by itself inhibited the growth of S. aureus as well, and 5 mM vitamin C inhibited growth completely. The growth inhibition of E. coli was slightly but significantly better in the presence of both quercetin and vitamin C than in the presence of quercetin alone. Probiotic L. plantarum was resistant to quercetin in the presence and absence of vitamin C. Enhancement of quercetin's antimicrobial activity by vitamin C is partly explained by the stabilizing effect of vitamin C on quercetin. Even though the acidity of vitamin C contributes to the inhibition of S. aureus growth, neutralized vitamin C also inhibits the growth efficiently even without quercetin. Our results suggest that vitamin C affects the metabolism of S. aureus and that these changes are likely to result in the observed growth inhibition. Although vitamin C itself is a powerful antioxidant, its aerobic metabolism increases oxidative stress on bacterial cells. Vitamin C may therefore be a safe and natural alternative for restricting the growth of S. aureus when non-toxicity is required.
槲皮素是一种天然类黄酮，具有多种有益健康的作用。其生物活性受到低溶解度和对氧化降解敏感的限制，而这些因素在实验室研究中经常被忽视。我们研究了在其可溶浓度下槲皮素对金黄色葡萄球菌、大肠杆菌和植物乳杆菌的抗菌作用，并研究了抗氧化维生素 C 如何调节这些活性。在研究的细菌中，金黄色葡萄球菌最为敏感。培养 12 小时后，90µM 槲皮素使金黄色葡萄球菌的生长减少到对照培养物的 75%。1mM 维生素 C 与 90µM 槲皮素联合使用，使金黄色葡萄球菌的生长急剧减少到仅补充维生素 C 的对照培养物的 3%。有趣的是，维生素 C 本身也抑制了金黄色葡萄球菌的生长，而 5mM 维生素 C 则完全抑制了生长。与单独使用槲皮素相比，槲皮素和维生素 C 同时存在时大肠杆菌的生长抑制略好，但有显著差异。益生菌植物乳杆菌在有或没有维生素 C 的情况下都能抵抗槲皮素。维生素 C 增强槲皮素的抗菌活性部分是由于维生素 C 对槲皮素的稳定作用。尽管维生素 C 的酸性有助于抑制金黄色葡萄球菌的生长，但中和后的维生素 C 即使没有槲皮素也能有效地抑制生长。我们的结果表明，维生素 C 影响金黄色葡萄球菌的代谢，这些变化可能导致观察到的生长抑制。虽然维生素 C 本身是一种强大的抗氧化剂，但它的需氧代谢会增加细菌细胞的氧化应激。因此，当需要非毒性时，维生素 C 可能是限制金黄色葡萄球菌生长的安全且天然的替代品。
