Abstract
Lichens are a group of plants composed of fungus and alga, which occupy a peculiar position. Their metabolic products are so different from those of higher plants that they constitute a peculiar group in the world of organic chemistry. Of these usnic acid is the most widely distributed, being responsible for the antimicrobial activity of lichen.
In the earlier stages of investigation, the remarkable antitubercular activity of usnic acid was noted. Of late, its application has been expanded as an antiseptic into a variety of pharmaceutical preparations and cosmetics which has become important due to its wide antimicrobial spectra on gram-positive bacteria. It shows an antibacterial activity on Staphylococcus in a dilution of 320, 000. Since hexachlorophene has been restricted because of accidents which occurred in 1972 in France, the use of usnic acid in ointments and powders has become especially promising, being added at a level of about 0.36% proving sufficient.
Ehrlich's reagent has been widely known for its characteristic colour reaction with usnic acid. The reaction was adaptd to a quantification test by Jayasankar and Towers, Recently, both gas-liquid and high-performance liquid chromatographic methods have been developed for its specific determination.
