EVALUATION OF SOME TRADITIONAL THERAPEUTIC PROPERTIES OF USNEA LONGISSIMA (ASCOMYCOTA, LICHENIZED FUNGI): ANTIMICROBIAL, ANTIQUORUM AND ANTIOXIDANT

Abstract

Usnea longissima, fruticose lichen growing in the temperate region, is well known traditional medicinal herb and a reservoir of some unique secondary metabolites. Traditionally it has been commonly used as an antimicrobial agent for the treatment of ailments like tuberculosis, ulcers and skin diseases, etc. In our study, we evaluate antimicrobial, antiquorum sensing (QS) and antioxidant activity of Usnea longissima secondary metabolites extracted in acetone, methanol, and 70% hydroalcoholic solvents. Antimicrobial activity of extracts was evaluated against fungus (Aspergillus niger, Candida albicans) and six bacterial (Agrobacterium tumefaciens, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aerogenosa, Staphylococcus aureus, Streptococcus mutans) strains. Whereas anti-QS activity was tested against biosensor strain Chromobacterium violaceum (CV) MCC 2290 and antibiofilm activity was checked in two gram-negative bacteria (P. aeruginosa and E. coli), two gram-positive bacteria (Bacillus cereus and Staphylococcus aureus) and fungus (Candida albicans). Results of experimental data indicated that methanolic extract exhibited maximum activity against A. tumefaciens (24±0.2 mm) and C. albicans (30±0.3 mm) with the minimum inhibitory concentration of 300µg/mL and 200µg/mL respectively. Interestingly, we also observed that all extracts effectively inhibited quorum sensing in C. violaceum and biofilm formation in Bacillus cereus, Escherichia coli, Pseudomonas aerogenosa, Staphylococcus aureus, at the concentration (100-300 µg/mL), for Candida albicans (50-150 µg/mL). Usnea longissima extract showed strong reducing power and hydroxyl radical activity and low DPPH scavenging activity. The present study suggested that U. longissima possesses potential antimicrobial and antiquorum sensing activity. These biological properties could be attributed to its significant antioxidant potential which validates its traditional use as an antimicrobial herbal source.