Antimicrobial screening and characterisation of phytochemical compounds from the stem bark of Butyrospermum paradoxum

Abstract

There is a growing risk in bacterial and fungal infections as a result of increased resistance of the disease causing bacteria and fungi to the existing medicines. A lot of scientific research has therefore been directed to finding reliable alternatives to the synthetic antimicrobial agents and this has led to studies on natural products. In this study, the antimicrobial activity of the stem bark crude extracts and the pure compounds of Butyrospermum paradoxum was investigated. Extraction from the air dried powdered plant material was done sequentially using n-hexane, DCM, ethyl acetate and methanol respectively to obtain four crude extracts. The crude extracts obtained were subjected to silica gel column chromatography and further purification of different fractions was done using sephadex LH-20 to obtain pure compounds. Using various NMR techniques like 1HNMR, 13CNMR, COSY, HSQC and HMBC, the isolated bioactive compounds were characterized i.e. α-amyrin cinnamate (48), butyrospermol cinnamate (49), lupeol acetate (50) and lupeol cinnamate (51). The antimicrobial activity of the crude extracts against Salmonella typhi, Escherichia coli, Candida albicans, Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus was determined using the agar well diffusion assay procedure while the MIC and MBC was determined by using the broth dilution method. All the four crude extracts were found to be active against most of the selected microbial organisms. The hexane extract was most active against C. albicans with average diameter of zone of inhibition of 14.3 mm and least active against P. aeruginosa giving a diameter of zone of inhibition of 11 mm. The DCM extract was most active against S. aureus with average diameter of zone of inhibition of 16.3 mm and was also least active against P. aeruginosa giving a diameter of zone of inhibition of 13.7 mm. . Meanwhile the ethyl acetate and methanol extracts were most active against S. typhi with average diameter of zone of inhibition of 18.0 mm and 22.0 mm respectively. The MIC and MBC values of all the crude extracts ranged between 12.5 and 50 mg/mL. The methanol extract gave the least antibacterial activity with an average diameter of zone of inhibition of 9.7 mm against K. pneumoniae. The antimicrobial activity of isolated compounds 48 and 51 against S. typhi, E. coli, C. albicans, and S. aureus was also investigated. Compound 51 gave the highest activity against C. albicans with average diameter of zone of inhibition of 22 mm and with MIC and MBC values of 0.125 and 0.50 mg/ mL respectively. Meanwhile the least activity was noted on compound 48 against S. aureus with an average diameter of zone of inhibition of 17.0 mm and with similar MIC and MBC values of 0.25 and 0.50 mg/ mL respectively. The study showed that both crude extracts and isolated pure compounds from the stem bark of B. paradoxum have significant antimicrobial activity and therefore may be used as alternative antimicrobial agents in place of the synthetic agents.