Isolation and identification of usnic acid from Usnea articulata and evaluation of the antioxidant and antibacterial activities of its ethanol and acetone extracts

Abstract

In this study, the antioxidant and antimicrobial activities of Usnea articulata were investigated, and usnic acid was isolated and structurally characterized. Antioxidant activity and total phenolic content were evaluated in acetone and ethanol extracts of the species using the DPPH and Folin–Ciocalteu methods, respectively. Column chromatography was employed for the separation of lichen metabolites, while thin-layer chromatography and X-ray analysis were used for their identification and structural characterization. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the ethanolic extract of U. articulata. The MIC was 21.88 mg/mL for both Escherichia coli and Staphylococcus aureus, whereas the corresponding MBC was 43.75 mg/mL, indicating that the bactericidal concentration was twofold higher than the MIC. Overall, the findings demonstrate that the ethanolic extract of U. articulata exhibits detectable antioxidant and moderate antibacterial activities under the experimental conditions. These findings provide additional phytochemical and biological information on U. articulata and support further investigation of its bioactive constituents.