Evaluation of the antimicrobial activity of three medicinal plants of South India

The present study was carried out to evaluate the antimicrobial activity of the crude methanolic extracts of Memecylon malabaricum Clarke. (leaves), Cochlospermum religiosum Linn. (leaves and flowers) and Andrographis serpyllifolia Vahl. (leaves) using the standard disc diffusion assay against eight strains of bacterial species, viz., Staphylococcus aureus, Salmonella typhi, Enterobacter aerogenes, Pseudomonas aeruginosa, Xanthomonas oryzae pv. oryzae, Xanthomonas axonopodis pv. malvacearum, Bacillus cereus and Micrococcus sp. The extracts of the plants at a concentration of 1.25 mg/disc showed minimum to moderate activity against both Gram positive and Gram negative bacteria indicating a broad spectrum activity. A preliminary phytochemical screening was conducted on the selected plant extracts using standard qualitative procedures that revealed the presence of several secondary metabolites. The extracts failed to show antioxidant activity by reducing power assay. The result indicates the potential usefulness of these plants especially Memecylon malabaricum and Cochlospermum religiosum, in treating microbial infections in humans and plants and justifies the need for further investigations and characterization of the bioactive compounds present in the methanolic extracts of the plants.