Metabolite profile analysis and antimicrobial properties of Usnea pectinata, Parmotrema tinctorum and Parmotrema crinitum in Bukit Larut, Perak, Malaysia: a case study

This study investigated the antimicrobial activities and metabolic profiles of the lichens Usnea pectinata , Parmotrema tinctorum and Parmotrema crinitum from Bukit Larut, Malaysia. Acetonic lichen extracts were prepared and screened against Staphylococcus aureus , Escherichia coli and Candida albicans using the Kirby-Bauer disk diffusion assay. Only U. pectinata extracts inhibited S. aureus , likely imparted by the antibacterial compound usnic acid. Liquid chromatography mass spectrometry (LCMS) analysis, principal component analysis, partial least squares discriminant analysis and heatmap visualization, revealed distinct metabolic profiles between U. pectinata, P. crinitum and P. tinctorum , with U. pectinata having a higher number of detected lichen acids. Tandem LCMS identified depsides and depsidones in all three lichens, while dibenzofurans were unique to U. pectinata . Despite having antimicrobial lichen acids, both P. crinitum and P. tinctorum extracts showed no bioactivity, likely due to sub-inhibitory or sub-MIC concentrations of lichen acids present. Novelly, this study also reported original findings on the antimicrobial screening and metabolite profile of P. crinitum .