Comparative study of the essential oil composition and antimicrobial activity of Leonotis leonurus and L-ocymifolia in the Eastern Cape, South Africa

Species of Leonotis are among the frequently-used herbal remedies to treat various bronchial illness and epilepsy. The essential oils of the leaf and flower of L. leonurus and L. ocymifolia growing in the Eastern Cape of South Africa were analysed by GC-MS. Major constituents of the L. leonurus oils were limonene (7.2-15.6%), (Z)-beta-ocimene (7.5-10.8%), gamma-terpinene (4.0-4.7%), beta-caryophyliene (15.2-19.6%), alpha-humulene (4.6-6.5%) and germacrene D (18.9-20.0%), while the essential oils of L. ocymifolia had (Z)-beta-ocimene (13.0-15.2%), nonanal (5.5%) beta-caryophyllene (21.430.8%), alpha-humulene (9.1-11.6%), germacrene D (21.521.7%) and T-muurolol (4.6%) as the prominent compounds. The oils exhibited a broad spectrum antibacterial activity against Gram-positive (Bacillus subtilis, Bacillus cereus, Micrococcus kiristinae, Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Shigella sonnet) bacteria with MIC values ranging from 1.25-0.039mg ml(-1).