Antibacterial and Antioxidant Activities of the Essential Oil from Nauclea latifolia (Smith) Leaves

Abstract

Nauclea latifolia​ is a plant used in ethnomedicine as an antihypertensive, antibacterial, antimalarial and anti-HIV agent amongst other therapeutic uses. In this work, the essential oil composition, antioxidant and antimicrobial activities of Nauclea latifolia leaves were studied. The essential oil obtained by hydrodistillation in an all-glass Clevenger-type apparatus was analysed using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The antibacterial activity of the essential oil at 6.25 to 100 µg/cm³ was tested on the following microorganisms: Bacillus cereus, Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae using an agar diffusion process while the free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl was employed for the antioxidant assay. A total of fourteen compounds comprising 96.68% of the essential oil (0.26% (w/w) was obtained with the main constituents being (Z)-9-octadecenamide (36.83%), E-3-hexenyl butyrate (17.36%), (E)-9-octadecenamide (12.44%) and linalool (12.03%).The essential oil inhibited the growth of Klebsiella pneumoniae at all concentrations with the zone of inhibition ranging from 13 mm to 18 mm which was comparable to the 10 mm of Gentamycin (10 μg). Pseudomonas aeruginosa on the other hand showed inhibition only at 50 and 100 µg/cm³ and was resistant to Gentamycin (10 μg). The antioxidant activity of the oil (51.06%) showed mild radical scavenging activity compared to ascorbic acid (74.39%). The presence of the main constituents of this essential oil explains the uses of the plants traditionally in the treatment of diseases such as cough, wounds or sores, toothaches and diarrhoea sometimes caused by Klebsiella pneumoniae which  was sensitive to it.