The antibacterial activity of the n-hexane, acetone/dichloromethane, ethanol and aqueous extracts of twelve common medicinal plants from the Philippines obtained through pounding and solvent extraction was evaluated using disc Agar diffusion. The microorganisms tested were: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa. Susceptibility test results showed that different extracts (1000 mcg/disc) from ten plants inhibited growth with a mean zone of inhibition range of 15 to 30 mm against S. aureus, E. coii, and P. aeruginosa. The common medicinal plants which showed highly positive activity were Psidium guajava (guava), Eucalyptus globulus, Mangifera indica(Indian mango), Nasturtium officinale (Watercress), Pterygospermum oleiferum (Moringa),Carmona retusa (Wild tea), Citrus aurantifolia (Lemon), Citrus sinensis (Orange), Allium sativum (garlic), and Allium cepa (onion). Preliminary phytochemical screening revealed the presence of flavonoids, tannins, alkaloids, glucosides, saponins and steroids/terpenes. The results suggest that the different plant extracts contain bioactive constituent(s) particularly tannins, flavonoids, terpenoids and other glycosides with very strong antibacterial activity and validates the ethno-medical use in the treatment of bacterial skin diseases and other forms of bacterial infections. However, many reputed plant antibacterials have very variable activities depending on certain conditions.
Key words: Antibacterial, medicinal plants from the Philippines, n-hexane, acetone/dichloromethane, ethanol, aqueous extracts, Psidium guajava, preliminary phytochemical screening.
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