Triterpenoids from Vernonia auriculifera Hiern exhibit antimicrobial activity

Abstract

Phytochemical investigation of Vernonia auriculifera afforded farnesylamine, a sesquiterpene amine that has not been found previously in plant species, together with lupenyl acetate, oleanolic acid, β-amyrin acetate, β-amyrin, friedelanone, friedelin acetate, α-amyrin and β-sitosterol. The compounds were characterized using nuclear magnetic resonace (NMR) spectroscopy and comparison with literature values. The isolated triterpenoids exhibited moderate antibacterial activity; α and β-amyrin had minimum inhibitory concentration (MIC) of 0.25 mg/ml against Staphylococcus aureus,Bacillus subtilis, Enterococcus faecium and Staphylococcus saprophyticus while lupenyl acetate and oleanolic acid exhibited MIC of 0.25 mg/ml againstStenotrophomonas maltophilia. Sub-MIC exposure of β-amyrin acetate was effective in decreasing adhesion of S. aureus, Klebsiella pneumonia and E. faecium while oleanolic acid decreased adhesion of K. pneumonia and Pseudomonas aeruginosasignificantly at sub-MIC. These compounds show potential for synergistic coupling with antimicrobial agents to improve therapeutic efficiency, in the face of rising bacterial resistance.   Key words: Vernonia auriculifera, triterpenoids, farnesylamine, antibacterial activity.