Characterization of the anti-adhesive principle of a Pelargonium sidoides root extract (EPs® 7630) in the interaction of group A-streptococci and human laryngeal epithelia cells

Abstract

Recently, intriguing experimental research has shown an anti-adhesive capability of the aqueous-ethanolic root extract EPs® 7630 that prevents docking of group A-streptococci on human laryngeal epithelial HEp-2 cells [1]. The present work aimed to gain further insight into the underlying biologically active principle and to identify the components that account for the anti-adhesive activity of this herbal medicine. In a validated flow cytometry-based assay [2], fluorescent-labelled group A-streptococci were incubated with human epithelial (HEp-2) cells. Only after pre-treatment of S. pyogenes, EPs®7630, a methanol-soluble (MSF) and a methanol-insoluble fraction (MIF) inhibited the adhesion of the pathogen to the host cells by ca. 45%, ca. 30% and ca. 34%, respectively. This finding indicated that the anti-adhesive effects were due to interactions with binding factors on the bacterial surface. Treatment of the extracts with skin powder produced polyphenol-free samples. That these samples were devoid of any anti-adhesive activities clearly indicated that the present proanthocyanidins played a decisive role as anti-adhesive components. Comparative studies with chemically defined proanthocyanidins including A- and B-type oligomers identified the presence of pyrogallol B-ring elements of constituent flavanyl units (prodelphinidin nature) as important structural feature of the anti-adhesive principle of this herbal medicine. However, the targets on the bacterial cell surface remain unknown.