Philippine Science Letters
vol. 3 | no. 2 | 2010
published online September 3, 2010


ARTICLE


Antibacterial activities of fruticose lichens collected from selected sites in Luzon Island, Philippines


by Krystle Angelique A. Santiago1, Jayne Nicholei C. Borricano1, Joecela N. Canal1, Denisse Marie A. Marcelo1, Myleen Claire P. Perez1, and Thomas Edison E. dela Cruz1,2*

1Department of Biological Sciences, College of Science and
2Research Center for Natural Sciences,
University of Santo Tomas, Espaa, Manila 1015 Philippines



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Lichens are known prolific sources of biologically active natural products. Thus, our research study explores the antibacterial activities of lichen acids extracted from fruticose lichens and aims to identify their bioactive metabolites. Sixty-three lichens were collected from different sites in Luzon Island, Philippines: Bataan, Batangas, Benguet, Cavite, Laguna, and Quezon. Morphological characterization and biochemical tests were used to identify the collected fruticose lichens as Usnea baileyi (6), Ramalina dendriscoides (55), Stereocaulon massartianum (1), and Cladonia gracilis (1). The lichen thalli were air-dried and their secondary metabolites extracted with acetone. Lichen crude extracts were then tested against Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) and Gramnegative bacteria (Escherichia coli and Pseudomonas aeruginosa) using the paper disk diffusion assay. Our results showed that all 45 tested extracts inhibited at least one of the test bacteria. However, only 38 extracts were found to be very active (> 19 mm zone of inhibition) against Gram-positive bacteria. Extracts from R. dendriscoides were observed to be the most active. Selected lichen extracts also showed activities against S. aureus even at a volume of 30 l and MIC/MBC values of 156 g/ml and 2500 g/ml in the tube dilution assay. Eight lichen acids were detected in the crude extracts by thin layer chromatography. TLC-bioautography showed barbatic acid, stictic acid, diffractaic acid, galbinic acid, norstictic acid, salazinic acid, and usnic acid to be the bioactive lichen acids.


*Corresponding author
Email Address: tedelacruz@mnl.ust.edu.ph
Submitted: November 5, 2009
Revised: August 10, 2010
Accepted: August 11, 2010
Published: September 3, 2010
Editor-in-charge: Eduardo A. Padlan
Reviewers: Esperanza C. Cabrera and Ma. Auxilia T. Siringan