Evaluation of the antibacterial activity of Ventilago madraspatana Gaertn., Rubia cordifolia Linn. and Lantana camara Linn.: isolation of emodin and physcion as active antibacterial agents

The antibacterial activity of the extracts of Ventilago madraspatana stem-bark, Rubia cordifolia root and Lantana camara root-bark, prepared with solvents of different polarity, was evaluated by the agar-well diffusion method. Twelve bacteria, six each of gram-positive and gram-negative strains, were used in this study. Chloroform and ethanol extracts of V. madraspatana showed broad-spectrum activity against most of the bacteria except S. aureus, E. coli and V. cholerae. On the other hand, the activity of the chloroform and methanol extracts of R. cordifolia and L. camara was found to be more specific towards the gram-positive strains, although gram-negative P. aeruginosa was also inhibited by the methanol extracts of both these plants in a dose dependent manner. The water extracts of V. madraspatana and L. camara were found to be inactive, while that of R. cordifolia was significantly active against B. subtilis and S. aureus compared with streptomycin and penicillin G used as standards. In the course of bio-assay guided fractionation, emodin and physcion were isolated for the first time from the stem-bark of V. madraspatana. It was noteworthy to find the MICs of emodin in the range 0.5-2.0 microg/mL against three Bacillus sp. Both the anthraquinonoid compounds inhibited P. aeruginosa, emodin being more effective, showing an MIC of 70 microg/mL.