Biological activities of essential oils and methanol extracts of five Ocimum species against pathogenic bacteria

Abstract

The essential oils and methanol extracts of Ocimum basilicum L., Ocimum kilimandscharicum Guerke, Ocimum gratissimum L, Ocimum canum Sims, and Ocimum tenuiflorum L. (green type) were examined for their potential antibacterial activities. The chemical composition of essential oils of Ocimum species was analysed by GC-MS. The inhibitory effects of essential oils and methanol extracts were studied on two Gram-positive (Bacillus subtilis, Micrococcus luteus) and five Gram-negative (Pseudomonas aeruginosa, Shigella dysenteriae, Escherichia coli, Vibrio cholera, and Shigella flexneri) bacteria using disc-diffusion method. Minimum inhibitory concentration (MIC) was assessed by micro broth dilution method. The antibacterial test results showed that the essential oils of Ocimum basilicum L., Ocimum kilimandscharicum Guerke, and Ocimum gratissimum L. strongly inhibited the growth of all of the microorganisms studied, especially of the Gram-negative strains, whereas other two essential oils showed moderate activities. The result may suggest that the essential oils of Ocimum possess compounds with antibacterial activities, and therefore could be used as natural preservative ingredients in food and/or pharmaceutical industries.