Characterization and antimicrobial activity of usnic acid from tropical lichens collected from Doi Suthep Pui, Thailand

Tanat  Tilapho; Suttinee  Kaewsriprakai; Vasun  Poengsungnoen; Kawinnat  Buaruang; Wetchasart  Polyiam; Chaisak  Chansriniyom; Ariya  Khanboon; Chatchai  Chaotham; Wongsakorn  Phongsopitanun; Trinset  Weeraphan

Authors

Tanat Tilapho Department of Chemistry, Faculty of Science, Srinakharinwirot University, Bangkok 10110, Thailand
Suttinee Kaewsriprakai Department of Chemistry, Faculty of Science, Srinakharinwirot University, Bangkok 10110, Thailand.
Vasun Poengsungnoen Lichen Research Unit, Department of Biology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand
Kawinnat Buaruang Lichen Research Unit, Department of Biology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand
Wetchasart Polyiam Lichen Research Unit, Department of Biology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand
Chaisak Chansriniyom Department of Pharmacognosy and Pharmaceutical Botany, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330, Thailand. Natural Products and Nanoparticles Research Unit (NP2), Chulalongkorn University, Bangkok 10330, Thailand
Ariya Khanboon Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330 Thailand
Chatchai Chaotham Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330 Thailand
Wongsakorn Phongsopitanun Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330 Thailand
Trinset Weeraphan Department of Biochemistry and Microbiology, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330 Thailand

Keywords:

Antimicrobial activity, Lichen secondary metabolites, Methicillin-resistant Staphylococcus aureus (MRSA), Natural product, Usnic acid

Abstract

Importance of the work: The potential as antimicrobial agents of usnic acid and other bioactive compounds from lichens was shown based on their effective inhibition of drug-resistant bacteria.

Objectives: To investigate antimicrobial properties of tropical lichen extracts, focusing on solvent extraction for usnic acid and other bioactive compounds.

Materials and Methods: In total, 14 lichen samples were collected from Doi Suthep Pui, Thailand. Secondary metabolites were extracted using chloroform and methanol. Antimicrobial activity was assessed based on agar disc diffusion against six bacterial strains and one yeast. Thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy were used to identify and purify bioactive compounds such as usnic acid.

Results: The chloroform extracts had higher antimicrobial activity than the methanol extracts. Usnic acid was detected in the chloroform extracts of samples PL05 and PL11-PL14 using TLC, with the yields of purified usnic acid from PL11-PL14 confirmed using NMR spectroscopy. Inhibition zone diameters against methicillin-resistant Staphylococcus aureus (MRSA) were in the range 12.5–19.0 mm for these samples. Notably, PL08 and PL09, without detectable usnic acid, still demonstrated strong antimicrobial activity, suggesting the presence of other bioactive compounds. Crude extract yields varied, with methanol producing higher amounts (16.4 mg/g for PL06) than chloroform (2.8 mg/g for PL01). The highest antimicrobial activity was observed against K. rhizophila, indicating susceptibility to lichen-derived compounds. These results underscored the potential of lichen extracts, particularly usnic acid, as antimicrobial agents.

Main finding: Usnic acid and other unidentified compounds from tropical lichens exhibited strong antimicrobial activity, particularly against MRSA, which highlighted the potential of lichen-derived bioactive compounds for developing novel antimicrobial agents against drug-resistant pathogens.