Antimicrobial Activity of Extracts from Fomitopsis betulina Strains Submerged Culture

Background . The basidiomycete Fomitopsis betulina represents a promising source of biologically active compounds. However, most studies have focused on its fruiting bodies, while the potential of submerged mycelial cultures remains insufficiently explored. Aim . To screen natural strains of F. betulina for the selection of the most promising producer of antimicrobial metabolites and to study the dependence of the antimicrobial activity of culture liquid extracts on cultivation conditions. Materials and methods . Strains of F. betulina were cultivated under submerged conditions. The antimicrobial activity of mycelial and culture liquid extracts was assessed using the agar well diffusion method and the broth microdilution method against Gram-positive and Gram-negative bacteria, as well as filamentous fungi. The trophic requirements of the lead strain were studied, and HPLC-MS analysis of its culture liquid extracts was performed. Results. Culture liquid extracts from all studied strains exhibited antimicrobial activity. F. betulina 2 and F. betulina 3 strains showed the highest target activity, with minimum inhibitory concentrations (MIC) of 320 µg/mL against pathogenic bacteria. Their active compounds were represented by both endoand exometabolites. F. betulina 3 strain was selected as the lead producer, as it demonstrated higher antimicrobial activity against a range of clinical isolates of pathogenic bacteria compared to F. betulina 2 strain. Enhanced activity was achieved through submerged cultivation using glucose as the carbon source in the nutrient medium. HPLC-MS analysis revealed a greater number of individual components when the producer was cultivated on medium F7. Conclusion. Culture liquid extracts of F. betulina 3 strain exhibited moderate activity against clinical isolates of Staphylococcus aureus and Staphylococcus haemolyticus according to the modified Kuete scale. A nutrient medium composition for submerged cultivation that increases the antibacterial activity of the extract is proposed.