Essential Oil of Otostegia integrifolia Benth: Composition, Antimicrobial and Antioxidant Activities

Abstract

Composition, antioxidant and antimicrobial activities of the essential oil of Otostegia integrifolia Benth. were studied. GC/MS analyses revealed the presence of 37 constituents representing 84.88% of the oil with α- pinene (31.33%), 1-octen-3-ol (11.78%) and trans-caryophyllene (11.35%) constituting more than 50% of its components. When tested for its antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), the oil reduced DPPH in a concentration dependent manner with an EC₅₀ value of 5.32 μl/ml. Similarly, the oil was shown to possess strong and broad spectrum antimicrobial activity against several Gram-positive and Gram -negative bacterial strains as well as fungal pathogens. The minimum inhibitory concentration (MIC) of the oil ranged from 5 to 100 μg/ml and 50 to 100 μg/ml against the bacterial and fungal strains tested, respectively. The oil (MIC=5 μg/ml) was found to be more potent than ciprofloxacin (MIC=10 μg/ml) against some E. coli strains. The antifungal activity of the oil was either comparable to or better than griseofulvin against most of the fungal pathogens tested. The study provides evidence for an excellent broadspectrum antimicrobial and significant antioxidant activity of O. integrifolia essential oil, a possible explanation for the traditional use of the plant.

Keywords: essential oil, Otostegia integrifolia, α-pinene, 2,2-diphenyl-1-picrylhydrazyl, antimicrobial activity