Antibacterial activity of crude extracts and pure compounds isolated from Vernonia galamensis leaves

The aim of this study was to test the antibacterial property of the extract of the leaves and isolated compounds of Vernonia galamensis that is traditionally claimed to have diverse medicinal use. The disk diffusion method was used to test the successively extracted dried leaves of V. galamensis on Staphylococcus aureus, Escherichia coli, Salmonella typhi and Shigella boydii. Further fractionation of the acetone extract by a combination of column chromatography, gel filtration using Sephadex LH-20 and Prep-TLC afforded two compounds. The results showed that Vernonia Acetone Extract (VAE) of the leaves of V. galamensis showed weak to moderate antibacterial growth inhibition on the test bacteria. Two active compounds; C-I (vernolide) and C-II (vernonioside) were isolated that were not reported from V. galamensis before. C-I (0.6 mg/disc) showed antibacterial activity on all bacteria except E. coli with minimum inhibitory concentration (MIC) value of 2.5 mg/mL and C-II (0.48 mg/disk) showed growth inhibition only against S. boydii and S. typhi with MIC value of 1 mg/mL. In conclusion, V. galamensis leaves have been proved to possess antibacterial chemicals. The plant can possibly be exploited as a source of lead compounds for antibacterial drug development.    Key words: Antibacterial, Vernonia galamensis, Staphylococcus aureus, Escherichia coli, Salmonella typhi, Shigella boydii, vernolide, vernonioside.