Antibacterial, Antioxidant Potency, and Chemical Composition of Essential Oils from Dried Powdered Leaves and Flowers of Hypericum revolutum subsp. keniense (Schweinf.)

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) was carried out by agar disk diffusion and microtiter broth dilution methods. Antioxidant activities of the essential oils were examined by different methods, DPPH, FRAP, and H2O2 assays. Chemical characterization was performed using gas chromatography interfaced with mass spectrometry, Fourier-transform infra-red (FTIR) spectroscopy, and 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 from 250 to 15.6250 μg/ml. The essential oils derived from the 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.

Antibacterial Potentials of Plants Used in Traditional Medicine of Rwanda

“…In contrast for Ocimum suave, saponins were present only in the stem, but tannins, phenol substances, flavonoids, alkaloids, and steroids were available in both leaves and stems [4]. The phenolic and flavonoid compounds were also reported by Sengera et al [23]. Saponins, tannins, glycosides, phenols, and resins were noticed in the Carduus nyassanus.…”

“…In Rwanda, Hypericum revolutum is used to cure malaria, tuberculosis, stomachache, dysuria, and urinary incontinence. In African traditional medicine, it is also utilized to combat wounds, diarrhea, nervous disorders, and rheumatism [23].…”

Phytochemical characterization, antimicrobial and antioxidant activities of Terminalia catappa methanol and aqueous extracts

“…Approximately 20 ml of the sterile media was poured carefully into each Petri dish, to produce a plate with uniform thickness of 4 mm. The media in the petri dishes was allowed to cool, producing a firm gel for plating [ 23 ]. After solidification of the media, the plates were inoculated by rubbing sterile cotton swabs that were dipped into bacterial suspensions over the entire surface of the plate [ 24 ].…”