Antimicrobial compounds from terminalia brownii against sweet potato pathogens

Phytochemical evaluation of Terminalia brownii extracts led to the isolation of five compounds namely β-sitosterol, stigmasterol, monogynol A, betulinic acid and arjungenin. Their structures were established by spectroscopic and physical methods as well as by comparison with literature data. The in vitro antimicrobial activities of the extracts and isolates were investigated against fungi and bacteria which infect sweet potato. Ethyl acetate extract exhibited the highest (p ≤ 0.05) antifungal and antibacterial activities compared to n-hexane and methanol ones. Streptomyces ipomoeae was more susceptible to ethyl acetate extract (inhibition zone, 18.6 mm) than streptocycline used as a positive control. The minimum inhibitory concentration (MIC) for the isolates ranged between 50 and 200 μg/ml with the lowest MIC value of 50 μg/ml being observed with betulinic acid against Aspergillus niger and S. ipomoea.