Baral B., Shrestha Vaidya G., Laxmi Maharjan B., Teixeira da Silva J. A.

Phytochemical and antimicrobial characterization of Rhododendron anthopogon from High Nepalese Himalaya [Fitocheminės ir antimikrobinės Rhododendron anthopogon iš Aukštųjų Nepalo Himalajų savybės]

Abstract The biological and chemical properties of the medicinally important high altitudinal plant Rhododendron anthopogon D. Don were assayed. Extracts at a concentration of 100 mg·ml-1 from leaves and flowers were collectively obtained by employing hot extraction method with different solvents. The antibacterial and antifungal properties were assayed against different clinical bacteria (two Gram+ and six Gram–) and six phytopathogenic fungi. Klebsiella pneumoniae and Salmonella typhimurium were the most inhibited bacteria, while Fusarium eridiforme, a fungus, was highly inhibited. However, all the tested bacteria were resistant to n-hexane and chloroform extracts. Of all the extracts obtained, the ethyl acetate fraction, followed by the hot methanolic extract, was effective against all the pathogenic strains tested. The MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) values of ethyl acetate and aqueous extracts on bacteria ranged from 1.562 mg·ml-1 to 25.0 mg·ml-1, whereas MIC and MFC (minimum fungicidal concentration) values of n-hexane and ethyl acetate fractions on fungi varied from 1.562 mg·ml-1 to 12.50 mg·ml-1, which are slightly higher than expected. The extracts showed no activity against Exserohilum turticum and Stenophylum sp. There was a highly significant difference in the zone of inhibition between different extract fractions and bacterial or fungal strains. A preliminary qualitative phytochemical assay revealed the presence of polyphenols, reducing compounds, quinones, sterol, triterpenes and fatty acids in leaves and flowers of the test plant. The observed antimicrobial effects are believed to be due to the presence of these compounds. The broad spectrum of activity of the extracts would apparently explain the widespread use of this plant for controlling human pathogenic bacteria and phytopathogenic fungi that widely destroy crops in Nepal. This research reveals R. anthopogon to be a highly promising source of potent antimicrobial drugs that could be used to design therapeutic drugs in the pharmaceutical industry.

Doi https://doi.org/10.2478/botlit-2014-0009

Keywords bacteria, fungi, microbes, phytochemical constituents, plant extract, zone of inhibition

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