Relation between Chemical Constitutions and Antibacterial Effects of Usnic Acid and its Derivatives

Abstract

Antibacterial effects in vitro of usnic acid, a component of lichens of Usnea specie, and its derivatives were tested. Usnic acid and its derivatives have growth inhibitory actions against Gram-positive bacteria. Usnic acid inhibits the growth of avian type tubercular bacilli after 10 days' incubation at 160, 000 dilution and that of Staphylococcs aureus after 24 hours at 160, 000-320, 000 dilution. Antibacterial activities against avian tubercular bacilli of usnic diacetate and dihydro-usnic acid are 1/2 to 1/4 that of usnic acid, this decreasing to 1/16 in that of dihydro-usnic acid diacetate (Table I.). These experiments prove that the antibacterial activity of usnic acid is controlled by the presence of 2 hydroxyl radicals and α, β-unsaturated ketone.