Phytochemical characterization and bioactivity evaluation of Himalayan lichen Usnea lapponica Vain.: antioxidant, antibacterial, and antibiofilm effects

This study investigated the chemical composition and biological activity of acetone and methanol extracts of the little-studied lichen species Usnea lapponica Vain. (U. lapponica), from Pakistan. Phytochemical analysis using HPLC-DAD and HPLC-MS confirmed the presence of salazinic acid, usnic acid, and arabitol. The acetone extract contained higher levels of total phenols (45.948 mg GA/g) and flavonoids (9.066 mg RE/g) than the methanol extract. Antioxidant activity, assessed via DPPH (2,2-diphenyl-1-picrylhydrazyl) and reducing power assays, was stronger in the acetone extract (IC50 = 140.099 µg/mL; A = 0.509) than in the methanol extract (IC50 = 192.961 µg/mL; A = 0.410), although both were less effective than ascorbic acid. Antibacterial testing showed that both extracts had stronger effects on Gram-positive bacteria, particularly Staphylococcus aureus and Bacillus cereus, with MIC values of 0.078 mg/mL and 0.156 mg/mL, respectively. Antibiofilm assays revealed up to 100% inhibition of biofilm formation in Staphylococcus aureus, while effects on mature biofilms were weaker.