Isolation, Chemical Characterization, and Antimicrobial Activity of Secondary Metabolites from Pseudocyphellaria faveolata

Introduction: Antimicrobial resistance is a global threat, highlighting the urgent need for novel antimicrobial agents. Among the mechanisms of resistance, bacteria can release drug-degrading enzymes and express efflux pumps, as well as grow in protected aggregates known as biofilms. Pseudomonas aeruginosa and Staphylococcus aureus are among the most prevalent biofilm infections in chronic wounds, respiratory and urinary tract infections, and device-associated infections. Pseudocyphellaria faveolata (Delise) Malme is a lichen with metabolites with unexplored antimicrobial potential. Aims: To identify and characterize the major metabolites present in Pseudocyphellaria Faveolata and to determine their antimicrobial activity against Staphylococcus aureus and Pseudomonas aeruginosa. Methods: The molecules were purified by column chromatography and characterized by NMR spectroscopy. The antimicrobial activity of the compounds was determined in terms of proliferation, adhesion, and viability against P. aeruginosa and S. aureus by the broth microdilution method and crystal violet staining. Viability was determined by the resazurin reduction assay on normal human fibroblasts to determine cytotoxicity over human cells. Results: The major metabolites were spectroscopically characterized and identified as physciosporin and methyl virensate. Physciosporin showed antimicrobial activity on S. aureus, with a MIC of 32 mu g/mL and MBC of 128 mu g/mL, and prevented biofilm formation from 16 mu g/mL. Methyl virensate also had antimicrobial activity on S. aureus (MIC = 64 mu g/mL). None of these metabolites significantly affected P. aeruginosa proliferation, viability, or adhesion. Cytotoxicity of physciosporin at 16 ug/mL on normal human fibroblasts was below 20%. Conclusions: This is the first report on the study of the antimicrobial activity of these compounds. Physciosporin showed promising activity in preventing the formation of S. aureus biofilms, which are responsible for chronic infections. These findings provide a foundation for exploring the antimicrobial potential of other lichenic depsidones.