Influenza virus variants with reduced susceptibility to inhibition by a polyphenol extract from Geranium sanguineum L.

A polyphenol extract obtained from the Bulgarian medicinal plant Geranium sanguineum L. (PC) inhibited influenza virus reproduction in vitro, in ovo and in vivo. The inhibitory activity of the plant preparation was proved to be selective and specific. Two variants of the virus A/chicken/Germany/34, strain Rostock (H7N1) (A/Rostock) with reduced drug sensitivity were selected by following passages in chicken embryo fibroblast (CEF) cells in the presence of inhibitory concentrations of the substance and by subsequent purification of resistant plaques (A/Rostock-R). PC affected to a lesser extent the biological activity and the infectivity of the resistant variants compared to the sensitive parent. The lower susceptibility of the variants was consistently observed in contact assay, ELISA, cytopathogenic effect reduction, plaque reduction and infectious virus yield reduction assays. Virus-specific protein synthesis in CEF cells infected with the resistant variants, determined by 35S-labelling and following SDS-PAGE, was also less sensitive to inhibition with PC.