Assessment of phytochemical content, antioxidant and antibacterial activities of three medicinal plants of Nepal

Three indigenous medicinal plants, Hibiscus rosa-sinensis L., Phlogacanthus thyrsiformis Mabb. and Lygodium japonicum (Thunb.) Sw., have been investigated for their phytochemical constituents, antimicrobial and antioxidant activities. All the three plants tested were positive for polyphenols, terpenoids, glycosides, saponins, flavonoids and reducing sugar. The ethanol extract of these medicinal plants were subjected to evaluate their antibacterial properties against four gram negative (that is, Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Proteus mirabilis) and two gram positive bacteria (that is, Staphylococcus aureus, Bacillus subtilis) by agar well-diffusion method. The ethanol extracts of the three plants prevented the growth of both gram-positive and gram-negative bacteria. The zones of inhibitions obtained ranges from 7±0.17 to 18.3±0.26 mm. Among these three plants extracts, H. rosa-sinensis was the most efficient against bacterial activity. Antioxidant activity of the extract was tested using scavenging activity of 1, 1-diphenyl-2- picrylhydrazyl (DPPH) radical method. Based on the result obtained, L. japonicum was found to have the highest antioxidant activity (IC50 = 80±1.3 µg/ml) followed by P. thyrsiformis (IC50 = 127±1 µg/ml) and H. rosa-sinensis (IC50 = 225±1 µg/ml). The results were compared with antioxidant activity of ascorbic acid (IC50 = 54±0.5 µg/ml). This study thus suggests that these three plants have great pharmacological importance since they have potent biological activities. Key words: Natural products, Escherichia coli, Staphylococcus aureus, Bacillus subtilis polyphenols, biological activity, agar well diffusion method.