Abstract

Acetone extracts of the leaves of Rhus Leptodictyawere studied for antibacterial activity usingbioautography and micro titre plate assay techniques against four nosocomial bacterial pathogens - Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, andEnterococcus faecalis. A bioassay guided fractionation showed that the activity was concentrated in the carbon tetrachloride fraction. A bioautography fingerprint showed that three major compounds were responsible for the antibacterial activity. Two of these compounds were isolated by a combination of solvent - solvent fractionation and chromatographic techniques. They were characterised by ¹HNMR, ¹³CNMR and 2D-NMR as 2,3-dihydro-amentoflavone, a biflavonoid andlutein, a carotenoid. This is the first report on the isolation of bioactive compounds from Rhus leptodictya.The four test organisms were sensitive to the two bioactive compounds. We found that Gram-positive organisms were more sensitive to 2,3-dihydro-amentoflavone with MIC values of 0.03 and 0.02 mg/ml to E. faecalis and S. aureus, respectively; while Gram-negative organisms were more sensitive to Lutein with MIC values of 0.06 and 0.09 to P. aeruginosa and E. coli, respectively. The cytotoxicity was determined using a methyl thiazole tetrazolium (MTT) based colorimetric assay against Vero monkey kidney cells. The MTT assay indicated that the LC₅₀ of 2,3-dihydroxy-amentoflavone to Vero cells was 9.4 µg/ml while the LC₅₀ of lutein was 9.8 µg/ml. Therefore, while the two compounds were very active against test organisms of nosocomial origin, they were also quite toxic.

Key words: Rhus leptodictya, bioautography, 2,3-dihydro-amentoflavone, lutein, anacardiaceae.