Antibacterial agents obtained from traditional medicinal plants are remarkable source for treating various diseases caused by micro-organisms. The three medicinal plants widely used in folklore remedies, showed high activity. Ethanol, Methanol, and n-hexane extracts of Psidium guajava L. leaves, Helianthus annus L. leaves and aerial parts of Mentha longifolia L. were screened for potential antibacterial activity against 5 bacterial strains, two Gram positive bacteria (Bacillus cereus and Bacillus subtilis) and three Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi) using agar well diffusion assay. Most of the extracts showed relatively high antibacterial activity against all the tested bacteria with the diameter of inhibition zone ranging between 8 and 30.1mm.The ethanolic extract was more active than methanol and n-hexane extracts. The n‐hexane extracts of most plants were inactive against Salmonella typhi. The most active extracts were those obtained from leaves of psidium guajava with inhibition zone30.1mm.The combined effect of ethanol extract of (Psidium guajava L /  Helianthus annus L) on bacterial species (B. subtilis, S. typhi) exhibited a higher zone (31.3mm) than that of any single extract. These medicinal plants could be a source of new antibiotic compounds; further work is needed, to isolate the secondary metabolites /natural products from the crude active extract.

Keywords: Psidium guajava, Helianthus annus, Mentha longifolia., Agar well diffusion assay,     Gram positive/ Gram negative bacteria