Identification and determination of usnic acid and fatty acid from various lichen species in arequipa, Peru, as well as antibacterial and antioxidant capacity

Seven species of lichens such us <i>Umbilicaria</i> aff. <i>calvescens</i>, <i>Hypotrachyna enderythraea</i>, <i>Punctelia graminicola</i>, <i>Cladonia chlorophaea</i>, <i>Xanthoparmelia farinose</i>, <i>Psiloparmelia distincta</i> (rock and tree substrates; rs and ts), and <i>Usnea durietzii</i> were collected from the province of Arequipa - Peru. Their usnic acid (UA) and fatty acid (FA) amounts in methanol-acetone were determined by High-performance liquid chromatography with diode-array detection (HPLC-DAD) and Gas chromatography-flame ionization detector (GC-FID). The antimicrobial activities of these extracts were evaluated against <i>Staphylococcus aureus</i> ATCC strains (43300, 29213, 25923 and 700699), <i>Escherichia coli</i> strains (O157:H7 and ATCC 10536), <i>Salmonella enterica</i> sv <i>typhimurium</i> ATCC 14028, <i>Candida albicans</i> ATCC 90028 and <i>Candida. tropicalis</i> ATCC 750T. In addition, antioxidant capacity was also studied by Total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical, 2,2-Azino-bis-3-ethylbenzothiazoline-6-sulfonic Acid (ABTS) radical cation and Ferric Reducing Antioxidant Power (FRAP) assays. The UA contents in all the studied lichen species varied between 0.017 and 0.304 %. Among all the tested extracts, <i>Usnea durietzii</i> had the highest total FA concentration (5.81 mg/g). <i>P. distincta</i> (rs) was active against <i>S. aureus</i> strains (MIC = 0.02-0.2 mg/mL) as well as <i>C. albicans</i> (MIC = 4 mg/mL) and <i>C. tropicalis</i> (MIC = 3 mg/mL). <i>P. distincta</i> (ts) displayed moderate total phenol content (TPC = 29.1 ± 1.6 mg GAE/g) and antioxidant capacity evidenced by scavenging DPPH (IC₅₀ = 1.45 ± 0.03 mg/mL) and ABTS (18.2 ± 0.2 mg TE/g) radicals, but it showed high values of FRAP (1953 ± 87 μM Fe²⁺/g). Our findings indicate that <i>P. distincta</i> (rs) could be considered as a potential antimicrobial metabolites source whereas <i>P. distincta</i> (ts) and <i>Puntelia graminicole</i> for polyphenols with antioxidant compound.