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.
