Antimicrobial Property of Extracts of Indian Lichen against Human Pathogenic Bacteria

Context.Usnea ghattensisG. Awasthi (Usneaceae) endemic fruticose lichen found growing luxuriantly in Northern Western Ghats of India, it also contains Usnic acid as a major chemical and tested against some human pathogenic bacteria.Objective. To explore antimicrobial properties ofUsnea ghattensisagainst some human pathogenic bacteria.Materials and Methods. The lichen was extracted in acetone, methanol, and ethanol.In vitroantimicrobial activity was tested initially byKirby-Bauertechnique of disc diffusion method and was confirmed by minimum inhibitory concentration using Broth microdilution method according to the NCCLS guidelines.Results. Ethanol extract was most effective againstBacillus cereusandPseudomonas aeruginosawith a zone of inhibition 29.8 ± 0.6 mm and 12.3 ± 0.5 mm diameters at a concentration of 0.2 mg/mL. Acetone and methanol extract demonstrated almost similar activity againstStaphylococcus aureusand the zone of inhibition was 24.6 ± 0.5 and 24.7 ± 0.4 mm. Only methanol extract was showing activity againstStreptococcus faecaliswith a 13.5 ± 0.8 mm zone. MIC value noted againstStaphylococcus aureusandStreptococcus faecaliswas 6.25 μg/mL and 25 μg/mL, whereas againstBacillus cereusandPseudomonas aeruginosa, MIC calculated was 3.125 μg/mL and 200 μg/mL, respectively.Conclusion. The present study demonstrates the relatively higher activity of this lichen against not only gram (+) but significantly also against gram (−) bacteria. This indicates that this lichen might be a rich source of effective antimicrobial agents.