Antibacterial, antioxidant potency and chemical composition of essential oils from dried powdered leaves and flowers of Hypericum revolutum subsp. keniense (Schweinf.)

Abstract

Abstract Hypericum revolutum subsp. keniense is a plant mainly used to treat diarrhoea, rheumatism, nervous disorders and wounds in African traditional medicine. The objective of the current work was to establish antibacterial, antioxidant potency and chemical composition of essential oil from the leaves and flowers of Hypericum revolutum subsp. keniense. The oils were isolated by steam distillation. Antibacterial activity against methicillin-resistant Staphylococcus aureus, Staphylococcus aureus (ATCC 12393), Escherichia coli (ATCC 25922), Acinetobacter baumannii (ATTC 19606), Salmonella Enteritidis (NCTC12023), Salmonella Typhimurium (ATCC 14028), Pseudomonas aeruginosa (ATCC 15442), and Haemophilus influenzae (ATCC 49766) were done by Agar Disk Diffusion and Microtiter Broth Dilution methods. Antioxidant activities of the essentail oils were examined by different methods, DPPH, FRAP and H2O2 assays. Chemical characterization was done using Gas Chromatography interfaced with Mass Spectrometry, Fourier-Transform Infra-red (FTIR) spectroscopy and the quantification of phenolics and flavonoids by Folin-Ciocalteu reagent and Aluminium nitrate respectively. The oils showed potential antibacterial activity with mean zone of inhibition ranging from 20.67 ± 0.33 to 32.00 ± 1.00 mm at 100 % oil concentration against the tested bacteria. Furthermore, the minimum inhibitory concentrations (MICs) in all the tested microorganisms were in the range of 250 to 15.6250 µg/ml. The essential oils derived from th leaves revealed varied antioxidant activity levels with the different methods of assay. The IC50 of values obtained from the three methods, DPPH, FRAP and H2O2 were ˃1000 µg/ml, 0.31 µg/ml and 12.33 µg/ml respectively. Caryophyllene (22.1 %) and 2,3,4-trimethylhexane were the major chemical components of the essential oils derived from the leaves and flowers respectively. FTIR spectroscopy of the essential oils from the leaves and flowers showed similarity at peaks for hydroxyl, unsaturated olefinic and amine functional groups. Further findings indicated that the total phenolic and flavonoid contents essential oils derived from leaves were 130.4 6 ± 10.5 mg GAE/g dry weight and 0.911 ± 0.04 mg CE/g dry weight respectively. It was therefore concluded that essential oils from the leaves and flowers of H. revolutum subsp. keniense have compounds that have antibacterial and antioxidant potency.