Oleanolic acid: an antimycobacterial component of Syzygium aromaticum L. and inhibitor of efflux mediated drug resistance.

Oleanolic acid (OA) was isolated from Syzygium aromaticum L. buds, and structurally characterised using different spectroscopic techniques; MS, IR, 1 H/ 13 C-NMR and 2D NMR experiments. The antimycobacterial activity according to a resazurin microtiter assay (REMA) showed important inhibitory effect of OA on the virulent H 37 Rv strain, with the lowest minimum concentration of 50 µg/mL, compared to other fractions. Molecular docking of OA with BacA drug efflux pump resulted in good binding affinity of hydrophobic interaction type. Therefore, OA could contribute to the antimycobacterial action of clove buds, and has potential as an efflux pump inhibitor. Further studies are required on its use to combat multidrug resistant strains.