Identification of foliose lichens and antibacterial screening of Parmotrema neopustulatum collected from communal forest in Shilan, La Trinidad, Benguet, Philippines

Lichens are symbiotic organisms composed of a mycobiont and a photobiont of either algae or cyanobacteria. Despite the reported 1,262 lichen species in the Philippines, the biodiversity and bioactivity of lichens in some areas of the Philippines remained understudied. In this study, we collected foliose lichens from a communal forest in Shilan, La Trinidad Benguet, Philippines, and subjected them to morphological and chemical analysis. A total of 19 lichen species were identified belonging to six genera, including Bulbothrix, Crocodia, Heterodermia, Hypotrachyna, Parmotrema, and Relicina. Specifically, Parmotrema neopustulatum, the most collected lichen thalli by mass, was extracted using ethyl acetate and was evaluated for its antibacterial properties against ESKAPE pathogens via paper-disk diffusion assay. The crude extract exhibited inhibitory activity against Enterobacter aerogenes, with a 13 mm zone of inhibition (ZOI). It also inhibited the growth of Staphylococcus aureus (18 mm ZOI), Klebsiella pneumoniae (21 mm ZOI), Acinetobacter baumannii (17 mm ZOI), and Enterococcus faecalis (16 mm ZOI). Based on Thin-Layer Chromatography (TLC), the extract contained aldehydes, alkaloids, cardenolides, essential oils, indoles, and sugars. This study addresses research gaps in Philippine lichenology, confirms the diversity of understudied foliose lichen species in some regions of the country such as La Trinidad, Benguet, and affirms that lichens are a potential source of bioactive secondary metabolites.