P131: Antioxidant and antibacterial properties of a lichen species isolated from the Black Hills, South Dakota

The Black Hills of South Dakota are renowned for their plant and microbial biodiversity. With respect to the latter, the lichen species of Black Hills were taxonomically examined and described approximately two decades ago. However, to date their biopharmaceutical potential remains scantly explored. The aim of this study was to examine and evaluate the antioxidant and antibacterial potential of the lichen Xanthoparmelia somloensis, isolated from the Black Hills in South Dakota. The antioxidant activity of the lichen methanol and ethanol extracts was assessed using a free radical scavenging assay and lipid peroxidation inhibition. A free radical scavenging activity of 77% (acetone extract) and 65% (methanol extract) was determined. The lipid peroxidation reaction of these extracts was inhibited 85% and 81%, respectively. The antibacterial activity was assayed against four clinical strains using the agar well diffusion method. Except for Escherichia coli, both extracts were found inhibitory to Streptomyces aureus, Streptococcus pyogenes,and Steptococcus agalactiae with a minimum inhibitory concentration of 0.7 to 0.9 mg/ml. This revealed the antimicrobial potential of lichen extracts against gram-positive microorganisms. It was demonstrated that both the antioxidant and antibacterial activities correlated well with the protein to polysaccharide ratio rather than the polyphenol content of the lichen extracts. The results reported here warrant further investigations to establish the usefulness of X. somloensis in biomedical applications such as treatment of multiple antibiotic resistant microbes and urinary tract infections without affecting the beneficial E. coli microflora.