The present invention relates to a biologically active supplement formulated in an oral dosage form comprising nutraceutically effective amounts of an extract of usnea barbata lichen, three-lobe beggarticks herb and common barberry berries and having an over-cumulative antibacterial, including bactericidal, action against the wide range of pathogens and conditional human pathogens, as well as over-cumulative antifungal action, including fungistatic and fungicidal actions. In addition, the supplement can comprise black elder berry extract, Baikal skullcap root extract, and fermented black garlic powder. The biologically active supplement of the invention can be used for enhancement of the general non-specific resistance of the body and for prevention or adjuvant therapy of the wide range of bacterial and fungal infections.