Phytochemical investigation of olea europaea stems bark and evaluation of its antimicrobial activities

Abstract

Medicinal plants play a significant role in the treatment of different diseases. The Olea europaea subsp. cuspidata is known by vernacular names “Ejersa” in Afaan Oromo and “Weyira” in Amharic, is one of the medicinal plants used by communities for the treatment of headaches, urinary tract /bladder/ infections, febrifuge and tapeworm; however, the phytochemicals and the biological activities of this plant have not exhaustively been reported. Therefore, the objective of this study was to isolate and characterize bioactive natural products from the stem bark of Olea europaea subsp. cuspidata. The air dried plant material was extracted sequentially with petroleum ether, chloroform, acetone and methanol at room temperature by cold maceration method. The antibacterial and antifungal activities of the extracts were evaluated against four pathogenic bacterial strains (B. cereus ATCC 10876, S. aureus ATCC 25923, E. coli ATCC 25922 and P. aeruginosa ATCC 27853) and two fungal strains (Fuzarium spp. and S. cerviceas) using agar disc diffusion method. The chloroform extracts showed good activity with the inhibition zone diameter of 8-10 mm against tested bacteria and marginal antifungal activity. Following its good activity, the chloroform extract was subjected to column chromatography for isolation of compounds, elution was carried using petroleum ether with increasing amounts of ethyl acetate and 298 fractions were obtained. Based on TLC profile, 10 fractions (F 232-241) obtained from crude by using 36% up to 32% petroleum ether in ethyl acetate were combined. For further purification, the combined fractions were subjected into Sephadex LH-20, eluted using 50% chloroform in methanol, and one pure compound was isolated. The structure of the isolated compound was characterized by spectroscopic techniques such as 1 H-NMR, 13 C-NMR and DEPT-135 NMR. The isolated compound is found to be (2-methylbenzofuran-6-yl)methanol and it show activities against all the tested strains, with the highest activity was observed against B. cereus and S. aureus bacterial strains. Devising alternative method of extraction as well as further isolation and characterization of bioactive compounds from this plant are recommended.