Chemical composition and in vitro antibacterial activity of three lichen species (Usnea sp., Thamnolia vermicularis subsp. solida and Ramalina asperula) collected from the Jauja and Huaral provinces-Peru

Introduction: Lichens are complex organisms conformed by a symbiotic association between algae and fungi; they are haven considerable interest owing to their pharmacological properties. Objectives: To determine chemical composition of the fatty acid (FA) and the percentage of usnic acid (UA), and to evaluate the in vitro antibacterial activity of the ethanolic extract obtained from the lichens Usnea sp., Thamnolia vermicularis subsp. solida and Ramalina asperula. Materials and Methods: Organic extracts from the three lichens were obtained using a rotary evaporator, soxhlet extractor and ultrasound equipment. The chemical composition of FA was determined by gas chromatography-flame ionisation detector, and the percentage of UA was quantified by UV-Vis spectroscopy. The in vitro antibacterial activity of the lichen ethanolic extracts was evaluated against E. coli ATCC 25922, Bacillus subtilis ATCC 11774, Staphylococcus aureus ATCC 43300 and S. aureus ATCC 29213 using the diffusion and microdilution methods. The minimum inhibitory concentration (MIC) was determined. Results: In the three tested lichens, the identified FAs were palmitic, stearic, oleic, linoleic, and linolenic acids; and the obtained percentage of UA was between 0.2 and 1.07 %. All the ethanolic extracts obtained from three lichens showed a high activity against B. subtilis (MIC = 0.5 mg/mL), while the ethanolic extracts obtained from T. vermicularis subsp. solida and R. asperula showed moderate activity against S. aureus ATCC 43300 (MIC = 3 and 1 mg/mL) and S. aureus ATCC29213 (MIC = 4 and 1 mg/mL). Conclusions: Our findings found for the three studied lichens confirmed the presence of some FAs and AU. These species provide an acceptable nutritional content and besides they can be considered as potential antibacterial agents.