Cytotoxicity and antibacterial activity of extractives from Wedelia calendulacea

The cytotoxicity and antibacterial activity of petroleum ether, chloroform and methanol extracts of Wedelia calendulacea were assayed by brine shrimp lethality bioassay and standardized disk diffusion method against 19 bacterial strains. Three diterpenes isolated from the plant were also evaluated for in vitro antibacterial activities. The LC50 for the crude extracts against the brine shrimp nauplii were found to be 4.59 microg/ml, 7.99 microg/ml and 14.88 microg/ml, respectively, whereas the positive control, vincristine sulfate showed an LC50 of 0.58 microg/ml. Among the crude extracts and pure compounds tested, (-)-kaur-16-en-19-oic acid isolated from the chloroform extract showed the highest inhibitory activity against most of the bacterial strains with mean zone of inhibition of 10-21 mm at 200 microg/disc.