Antimicrobial activity of the methanolic extract and compounds from Teclea afzelii (Rutaceae)

The methanolic extract (TAE) together with three alkaloids identified as Kokusaginine (1), Maculine (2), Kolbisine (4) and a common terpenoid, Lupeol (3), isolated from the stem bark of Teclea afzelii were tested for their antimicrobial activity against Gram-positive and negative bacteria, fungi and Mycobacterium smegmatis. Agar diffusion assay was used for the determination of the sensitivity of test organisms to the samples. The micro-dilution method to determine the Minimal Inhibition Concentration (MIC) and the Minimal Microbicidal Concentration (MMC). The results of the diffusion test showed that only compound 1 was active on all the tested micro-organisms, whilst the inhibition effect of the crude extract and that of compounds 2 and 4 was observed on 87.5% of the tested microbial species. The lowest MIC value (19.53 μg/ml) for the crude extract was obtained on Escherichia coli, Bacillus subtilis and Microsporum audorium. The corresponding value for the tested compounds (2.44 μg/ml) was recorded with compound 2 on B. subtilis. The crude extract, compounds 2 and 3 showed moderate activity against M. smegmatis. The overall results provide promising basis for the use of the crude extract as well as the isolated alkaloids in the treatment of specific microbial infections.