In-vitro antibacterial screening of extracts of usnea longissima lichen.

ABSTRACT

Objective: To evaluate the antibacterial activity of the hydroalcoholic and ethanolic extracts of the Usnea longissima lichen. Material and methods: Kirby Bauer's disk diffusion method and broth serial dilution tests according to CLSI Guidelines (2000) were used, to find out the antibacterial effect of the 50% Hydro-ethanolic and 90% ethanolic extracts of the selected lichen. The efficacy of the extracts were measured after the period of incubation as Zone of Inhibition (ZOI) in mm compared with the Standard drug used i.e. Ciprofloxacin for Gram positive and Gentamicin for Gram negative bacterial strains. MIC was further tested for susceptible organisms. DMSO was used as control. All the experiments were conducted in triplicates and in proper sterilized condition Results: It was found that Usnea longissima has a significant activity towards Bacillus cereus (ZOI 25-26 mm as compared to Ciprofloxacin ZOI-23 mm) MIC-0.625 mg/ml, Pseudomonas aeruginosa (ZOI 20-27 mm as compared to Gentamicin ZOI-14 mm) MIC- 1.25 mg/ml and Proteus vulgaris (ZOI of 13 - 16 mm where as Gentamicin produced ZOI as 14 mm) MIC 2.5 mg/ml. Moderate activity was shown towards Staphylococcus aureus, Corynebacterium xerosis, Escherichia coli and Klebseilla pneuomoniae while no activity towards S. epidermidis and S. pyrogenes. Moreover it was seen that 50% Hydro-ethanolic extracts produced more significant ZOI than ethanolic extract in all tested strains. Conclusions: U. longissima contains potent chemical constituents as Usnic acid which can halt infection and is effective against various gram-positive and gram-negative bacterial species. It can be concluded that due to their antimicrobial effects extracts of the lichen can be used for the infectious diseases caused by these microbes. This study provides an in-vitro proof of the antibacterial activity of Usnea longissima.