Antimycobacterial activity of usnic acid against resistant and susceptible strains of Mycobacterium tuberculosis and non-tuberculous mycobacteria.

Tuberculosis remains a serious public health problem, with nine million cases being reported annually. Treatment with antibiotics is the most effective mechanism to control this disease, although the increase in cases with resistant strains, co-infection with HIV, and the long duration of treatment has established the need to develop new drugs. Here we show the activity of usnic acid against susceptible and resistant Mycobacterium tuberculosis strains and against nontuberculous mycobacteria. Further, we did not identify any contribution of efflux in innate resistance to usnic acid.