Antimycobacterial activity of Usnea steineri and its major constituent (+)-usnic acid
The antimycobacterial activity of an extract of Usnea steineri and of its major constituent (+)-usnic acid was evaluated against Mycobacterium tuberculosis (ATCC 27294), Mycobacterium kansasii (ATCC 12478) and Mycobacterium avium (ATCC 15769). The acetone extract (ACE) of U. steineri displayed promising minimum inhibitory concentration (MIC) values of 32 ìg/ml against M. tuberculosis and 62 ìg/ml against both M. kansasii and M. avium. The isolated compound (+)-usnic acid was even more effective against the evaluated microorganisms with MIC values of 16 ìg/ml against M. avium and 8 ìg/ml against both M. tuberculosis and M. kansasii.
Key words: Usnea, usnic acid, antimycobacterial activity.