Chemical, Antibacterial And Antioxidant Properties Of Hypericum Revolutum Subsp. Keniense Essential Oils

Abstract

The plant Hypericum revolutum subsp. keniense is utilized in the treatment of stomach complaints, joint pains, nervous disorders, and skin illnesses. The present study aims at establishing phytochemical components in essential oil mixtures from H. revolutum subsp. keniense aerial parts. Antibacterial activities and scavenging of free radicals were also determined. Steam distillation was used to obtain the distillates containing the oils with aroma. The oils were then analyzed by Fourier Transform Infra-red (FTIR) spectroscopy and Gas chromatography-Mass Spectrometry. Further, the disk-diffusion and microtiter dilution methods were used to test the antimicrobial effects of the oil mixtures against bacterial strains, namely, MRSA, Staphylococcus aureus-12393, Escherichia coli-25922, Acinetobacter baumannii -19606, Pseudomonas aeruginosa-15442, and Haemophilus influenzae-49766, Salmonella Enteritidis-NCTC12023, and Salmonella Typhimurium-14028. Radical scavenging activities were examined based on 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH), ferric reducing antioxidant power (FRAP) and Hydrogen peroxide (H2O2) radical scavenging capacity assays. The quantity of phenolics was measured by Folin’s phenol reagent and that of flavonoids by Aluminium nitrate colorimetric assay. The FTIR spectrum revealed that the essential oils had functional groups including O-H, –CH (CH2), C=O, C=C-C, C-H and C-N. Further the compounds were analyzed using GC-MS and the major compounds detected were Caryophyllene (22.1 %) and 2,3,4-trimethylhexane (10.5%). The highest zone of inhibition that was recorded was 36.67 ± 0.88 mm (leaf essential oils) at 100 % oil concentration against A. baumannii. The lowest concentration of oil at which bacterial growth was completely inhibited (MICs) of 15.6250 μg/ml were recorded for MRSA, S. Enteritidis, P. aeruginosa and E. coli. The concentration that could scavenge 50% of the free radicals (IC50) was highest for DPPH (˃1000), while, lowest with FRAP (0.31) and H2O2 (12.33) μg/ml. It was concluded that the constituents of H. revolutum subsp. keniense essential oil mixtures had antibacterial and antioxidant potency.