The fermentation product, produced by Streptomyces sp. 225b (SS 225) selectively inhibited the reproduction of influenza virus A/chicken/Germany/34, strain Rostock (H7N1) in MDCK cells shown by the reduction of viral hemagglutinin (HA) expression on the surface of infected cells, virus-induced cytopathogenic effect, the production of HA and infectious virus. The inhibitory effect was dose-dependent and affected viral penetration and some intracellular stages of viral replication. No inactivating effect of the extracellular virus was found. Using representative strains of influenza virus it was shown that the inhibitory effect was strain-specific; most sensitive to inhibition were A/Rostock and A/PR8/34 (H1N1). In addition the preparation protected mice from mortality in the experimental A/Aichi/2/68 (H3N2) (A/Aichi) influenza virus infection; the mean survival time was prolonged the lung infectious virus titres and the lung consolidation were reduced in comparison with virus control.

SS 225 belongs to the group of serine proteinase inhibitors. It has been subjected to purification by ion exchange chromatography, gel filtration and HPLC analysis. It was a hydrophobic and a termostable protein, had a molecular mass of 11.1 kDa and a high content of hydrophobic amino acids.