In Vitro Antibacterial Activity of Aqueous and Acetone Extracts Obtained from Epiphytic Lichens

Lichens produce a wide variety of biologically active secondary metabolites that contribute to their ecological adaptation and pharmacological potential. This study was conducted to investigate the antibacterial effects of acetone and water extracts obtained from the lichen species Pseudevernia furfuracea (L.) Zopf, Platismatia glauca (L.) W.L. Culb, and Ramalina farinacea (L.) Ach on bacterial species such as Listeria innocua (Gram positive), Staphylococcus epidermidis (Gram positive), and Escherichia coli (Gram negative). The findings highlight the antibacterial potential of macrolichen species and suggest that they are promising natural sources for the development of plant-based antibacterial agents. The minimum inhibitory concentration (MIC) method was used to determine the antibacterial properties of lichens. MIC assessment revealed significant differences in antibacterial performance depending on both the lichen species and the solvent used for extraction. Among the analyzed samples, Ramalina farinacea (L.) Ach exhibited the broadest inhibitory activity range and effectively suppressed the growth of all tested bacterial strains at comparatively low concentrations. Pseudevernia furfuracea (L.) Zopf showed significant activity mainly against S. epidermidis, while Platismatia glauca (L.) W.L. Culb exhibited a narrower activity limited to the same microorganism. In contrast, all water-based extracts were found to be inactive, and visible bacterial growth was detected in each test well. These results indicate that acetone provides a more suitable medium for the isolation of lipophilic antibacterial compounds from lichen materials. Overall, the findings suggest that solvent polarity and species-specific metabolite composition play a critical role in shaping the antimicrobial potential of lichen-derived extracts.