Several compounds, whose structures represent the most common chemical classes of lichen metabolites, were screened for in vitro activity against Mycobacterium aurum, a non-pathogenic organism with a similar sensitivity profile to M. tuberculosis. Of the compounds tested, usnic acid from Cladonia arbuscula exhibited the highest activity with an MIC value of 32 μg/ml. Atranorin and lobaric acid, both isolated from Stereocaulon alpinum, salazinic acid from Parmelia saxatilis and protolichesterinic acid from Cetraria islandica all showed MIC values ≤125 μg/ml.
Bibliographical noteFunding Information:
The work was in part supported by the Icelandic Council of Science and the University of Iceland Research Fund. We thank Dr. Hordur Kristinsson for identification of the plant material and Dr. Sigrı́dur Jónsdóttir (Science Institute, University of Iceland) for recording 1 H and 13 C NMR data for usnic and salazinic acids.
- Lobaric acid
- Protolichesterinic acid
- Salazinic acid
- Usnic acid