Phenolic constituents and antimicrobial studies on the aqueous methanolic extract of the Plectranthus ecklonii leaves

The use of natural products with therapeutic properties is as ancient as human civilization and, for a long time, mineral, plant and animal products were the main source of drugs. Herbal medicines have been used to treat many diseases including several infections. Plectranthus species (Lamiaceae) have been used in popular medicine for analgesic and dyspeptic purposes. Plectranthus need to be well identified in order to be used as commercially genuine medicinal plant [1]. The present study deals with the isolation and identification of phenolic constituents from the leaves of Plectranthus ecklonii growing in South Africa, and evaluation of the antimicrobial effects of a methanol-water (70:30) extract. This extract of P. ecklonii was subjected to repeated chromatography on polyamide and Sephadex LH-20 columns resulting in vitexin, isovitexin, apigenin 7-O-β-glucoside, apigenin 4',6-dimethoxy-7-O-β-glucoside, luteolin 7-O-β-glucoside, apigenin, luteolin and caffeic acid. The structures of the isolated compounds were elucidated on the basis of spectral analysis. The hydroalcoholic extract of the leaves of P. ecklonii exhibited variable degrees of antimicrobial activity (diffusion method). The extract showed a moderate activity against Escherichia coli and Bacillus cereus (20mm diameter) and low activity against Bacillus subtilis (16mm diameter) compared with that exerted by antibiotics (MIC,1.020–3.05mg/ml). In addition, it was found inactive against Staphylococcus aureus and Streptococcus pyogens [2,3].

References: 1. Passinho-Soares, H. et al. (2006) Planta Med. 72: 929–31.

2. Zhu, X. et al. (2004)J. Agric. Food Chem. 52: 7272–8.

3. Chacha, M. et al. (2005) Phytochem. 66: 99–104.