Lichens are a source of natural compounds with antibacterial action due to many biologically active secondary metabolites. Usnea barbata (L.) F.H. Wigg. (U. barbata) contains mainly usnic acid, a secondary specific metabolite of the genus Usnea, and phenolic compounds. Thus, the objective of this study is to evaluate the antibacterial effect (ABE) of U. barbata extracts in relationship with the usnic acid content (UAC) and polyphenols content (PC) in each extract. Extraction was performed in acetone, ethanol and water, ten days in a plant room. The ABE of all three extracts was evaluated against Staphylococcus aureus and Pseudomonas aeruginosa. The results indicated that the acetone extract has the highest UAC, followed by ethanol and aqueous ones. The highest PC was found in ethanol extract, followed by aqueous and acetone ones. The most sensitive bacteria species was Staphylococcus aureus; also, ethanol extract has the highest ABE against both bacterial strains. It is followed by acetone extract; the aqueous extract has no antibacterial action on these two bacterial species. The high content in classic polyphenols and moderate UAC in U. barbata ethanol extract could explain the obtained results.

Acknowledgments: This work is supported by the project “ANTREPRENORDOC”, in the framework of Human Resources Development Operational Programme 2014-2020, financed from the European Social Fund under the contract number 36355/23.05.2019 HRD OP /380/6/13 – SMIS Code: 123847.