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Helicobacter pylori is a major etiological agent in gastroduodenal disorders. In this study, we isolated 36 polyphenols and 4 terpenoids from medicinal plants, and investigated their antibacterial activity against H. pylori in vitro. All hydrolyzable tannins tested demonstrated promising antibacterial activity against H. pylori. Monomeric hydrolyzable tannins revealed especially strong activity. Other compounds demonstrated minimal antibacterial activity with a few exceptions. A monomeric hydrolyzable tannin, Tellimagrandin I demonstrated time‐ and dose‐dependent bactericidal activity against H. pylori in vitro. On the other hand, hydrolyzable tannins did not affect the viability of MKN‐28 cells derived from human gastric epithelium. Hydrolyzable tannins, therefore, have potential as new and safe therapeutic regimens against H. pylori infection. Furthermore, we investigated effects of hydrolyzable tannins on lipid bilayer membranes. All the hydrolyzable tannins tested demonstrated dose‐dependent membrane‐damaging activity. However, it remains to be elucidated whether their membrane‐damaging activity directly contributes to their antibacterial action.

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An extract from Salvia officinalis (Sage) leaves showed antimicrobial activity against vancomycin-resistant enterococci (VRE). We isolated the effective compound and identified it as oleanolic acid, a triterpenoid. We also tested antimicrobial activity of similar triterpenoids, ursolic acid, uvaol, betulinic acid and betulin. We found that ursolic acid also showed antimicrobial activity against VRE. The minimum inhibitory concentrations (MICs) of oleanolic acid and ursolic acid were 8 and 4 m mg/ml, respectively. These two compounds also showed antimicrobial activity against Streptococcus pneumoniae and methicillin-resistant Staphylococcus aureus (MRSA). These compounds showed bactericidal activity against VRE at least for 48 h when added at concentrations that were two-times higher than their MICs.

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