Abstract
Bacterial adhesion to epithelial cells is a key step in infections, allowing subsequent colonization, invasion and internalization of pathogens into tissues. Anti-adhesive agents are therefore potential prophylactic tools against bacterial infections. The range of anti-adhesive compounds is largely confined to carbohydrate analogues. Tannins are generously recognized as potent antimicrobials, but little data exist on their anti-adherence potency. Using a model for mucosal pathogenesis with labeled group A-streptococci (GAS) and human laryngeal HEp-2 cells, a series of flavan-3-ols (epicatechin, epigallocatechin, epigallocatechin-3-O-gallate) and highly purified and chemically characterized proanthocyanidin samples including procyanidins based on epicatechin, catechin or ‘mixed’ constituent flavanyl units, prodelphinidins made up of (epi)gallocatechin monomeric unts as well as oligomers possessing A-type units in their molecules was evaluated for anti-adhesive effects. Reduced microbial adherence was observed exclusively for prodelphinidins, suggesting that pyrogallol-type elements, i.e., (epi)gallocatechin units are important structural features. This is the first report on structure-activity relationships regarding the anti-adhesive potency of proanthocyanidins. In addition, the structures of the first chemically defined proanthocyanidins from Pelargonium sidoides are disclosed.
Highlights
Proanthocyanidins represent a major group of polyphenols with amazing structural diversity that occur ubiquitously in woody and some herbaceous plants
Bearing in mind the well-known capabilities of proanthocyanidins to interact with macromolecules, including carbohydrates and proteins, members of this class of compounds may be another group of promising anti-adhesive compounds
Encouraged by the above findings, we extended our studies to a series of highly purified and chemically defined proanthocyanidin samples including epicatechin-based procyanidins from Nelia meyeri [15], catechin-based oligomers from Salix spp. [16], ‘mixed’-procyanidins from Betula spp
Summary
Proanthocyanidins represent a major group of polyphenols with amazing structural diversity that occur ubiquitously in woody and some herbaceous plants Their presence in significant amounts in the wood, bark, leaves and fruits of many plant species has suggested a crucial role at the ecological and evolutionary level [1,2]. Evaluation of the antimicrobial potency of a series of chemically defined tannins against a panel of microorganisms revealed only moderate growth inhibition, with minimum inhibitory concentrations (MIC) of 1,000 μg/mL for most samples [4] This apparent discrepancy between weak antimicrobial activities of distinct phenolic compounds in vitro and effective antimicrobial protection to plants as well as the claimed efficacy of herbal medicines may plausibly be explained by the large polyphenol concentrations in plants and traditional herbal preparations as well as the chemical heterogeneity. The paper presents results regarding the relationship between some flavan-3-ol/proanthocyanidin structures and adherence inhibitor activity in a model using group A-streptococci and human laryngeal epithelial (HEp-2) cells
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