Chemical Composition and Biological Activities of the Essential Oil of Plectranthus caninus Roth

The essential oil from the aerial parts of Plectranthus caninus roth (lamiaceae), obtained by hydro-distillation was analyzed by gas chromatography/mass spectrometry (gc/Ms) and evaluated for antimicrobial, free radical scavenging and anti-inflammatory activities. Thirty-four compounds representing 91.02% of the total oil were identified. the major constituents of the oil were camphor (22.36%) and a-thujene (14.48%). the oil was tested against 21 bacterial and 4 fungal strains using disc diffusion method and found to be active against a broad spectrum of pathogens including gram-positive and gram-negative bacteria as well as some fungal strains. the minimum inhibitory concentrations (MIcs) of the oil against the bacterial strains tested ranged from 10 to 400 µg/ml, and from 800 to 1000 µg/ml against the fungal strains employed. The in vitro antioxidant activity was assessed using 2,2-diphenyl-1-picrylhydrazil (DPPH) radical scavenging assay. The oil reduced DPPH in a concentration dependent manner with an EC50 value of 3.5 µl/ml. The in vivo anti-inflammatory activity was evaluated on the basis of inhibition of carrageenan-induced mouse hind paw oedema whereby doses of 200 and 300 mg/kg were found to inhibit significantly increase in paw volume during the late phase of inflammation. The study provides evidence for the broad-spectrum antimicrobial, significant antioxidant and anti-inflammatory effect of Plectranthus caninus essential oil, a possible explanation for the traditional use of the plant in the treatment of cold, teeth and gum disorders which may be related to microbial infections and inflammation.