Abstract

Cissus subaphylla and Euphorbia spiralis, endemic in Socotra Island, were screened for their chemical constituents and antibacterial activity. The phytochemical screening of the chloroform and the 70% ethanol extracts of both plant stems indicated the presence of sterols, triterpenoids, cardiac glycosides, anthraquinons, flavonoids, tannins and carbohydrates as chemical constituents. Testing the antibacterial activity of chloroform and the 70% ethanol extracts (5 and 10mg) of both plants against Staphylococcus aureus (305-864-669), Staphylococcus epidermidis (505-864-689), Pseudomonas aeruginosa(909-825-1793) and Escherichia coli(909-825-1793), using agar well diffusion assay, demonstrated that all tested extracts displayed a significant antibacterial activity with activity index (AI) above 0.5 against test microorganisms, except the chloroform extract of C. subaphylla, which was found inactive against S. aureus. The 70% ethanol extract (10mg)of E. spiralis showed the highest antibacterial activity (AI=0.80-0.94) against E. coli.