Electrophysiological and spectroscopic investigation of hydrolysable tannins interaction with α-hemolysin of S. aureus.

In this study, using bilayer lipid membrane technique, we report a novel facet of antihemolytic activity of two tannins (1,2,3,4,5-penta-O-galloyl-β-D-glucose (PGG) and 1,2-di-O-galloyl-4,6-valoneoyl-β-D-glucose (dGVG)), which consists in inhibiting the formation of α-hemolysin channels and blocking the conductivity of already formed channels. These effects were observed at tannin concentrations well below minimal inhibitory concentration values for S. aureus growth. Using spectroscopic methods, we show that these two tannins differing in molecular structure but having the same number of -OH groups and aromatic rings form firm complexes with hemolysin in aqueous solutions, which may underlie the disruption of its subsequent interaction with the membrane, thus preventing hemolysis of erythrocytes. In all experimental settings, PGG was the more active compound compared to dGVG, that indicates the important role of the flexibility of the tannin molecule in interaction with the toxin. In addition, we found that PGG, but not dGVG, was able to block the release of the toxin by bacterial cells. This toxin is a strong pathogenic factor causing a number of diseases and therefore is considered as a virulence target for treatment of S. aureus infection, so the data obtained suggest that PGG and possibly other tannins of similar structure have therapeutic potential in fighting the virulence of S. aureus.