Chemical composition and anti-microbial activity of essential oils of the plants: Tarchonanthus camphoratus, Leonotis nepetifolia and Satureja biflora

Abstract

In sub-Saharan Africa, the high infant mortality is mainly due to diarrhoea, respiratory infections, typhoid and measles. The control of these diseases relies heavily on the use of synthetic drugs. However, due to the high cost of these drugs and increased bacterial resistance to available anti-biotics, their use is increasingly becoming unpopular. Plant-derived herbal medicines are feasible alternatives that can be used to reduce incidence of these diseases. Since they are readily available and are not known to develop resistance. This study involved extraction of essential oils from fresh leaves of medicinal aromatic plants; Tarchonanthus camphoratus, Leonotis nepetifolia and Satureja biflora by hydro distillation using a modified Clevenger–type system. The oils were analyzed by gas chromatography–mass spectroscopy (GC–MS) and evaluated for anti-microbial activity. Subsequently, minimum inhibitory concentration was determined by serial dilution of the oils. Essential oil from Tarchonanthus camphoratus was obtained in 0.2% w/w yield with thirty-eighty identified components constituting 95.75%. The oil was dominated by monoterpenes, (80.86%). The main constituents were fenchol (15.86%), 1, 8-cineole (14.27%) and á-terpineol (13.21%). The oil showed broad-spectrum anti-fungal and antibacterial activity however Pseudomonas aeruginosa was found to be resistant to the oil. Leonotis nepetifolia oil was obtained in 0.004% w/w yield. A total of 36 compounds constituting 94.80% of the oil were identified. The oil was characterized by a high percentage of sesquiterpenes (75.32%). The major compounds were: germacrene D (37.16%), germacrene–D-4-ol (6.02 %,) and cis-ocimene (4.79%). This oil exhibited negligible antifungal and anti-bacterial activities against Staphylococcus aureus, Bacilllus spp, Salmonella typhi, Klebsiella pneumonia and Proteus mirabillis. Satureja biflora oil was obtained in 0.2% w/w yield; twenty-two components representing 99.29% of the total oil were identified. The vii oil was dominated by monoterpenes (62.02%). The major compounds were linalool (50.60%), germacrene D (10.63%) and linoleic acid (4.48%). The oil showed anti-bacterial activity against all the bacterial strains tested except Pseudomonas aeruginosa, and antifungal activity against Candida albicans. These findings may be used as leads in the search for new drugs from non-microbial sources.