Variation in Antimicrobial Activity of Warburgia ugandensis Extracts from Different Populations across the Kenyan Rift Valley
Warburgia ugandensis isa highly valuedmedicinal tree within East Africa which is over-exploited for its medicinal use among many communities. This species has its habitat encroached and this has led to a notable decrease in its population size to the level that warrant some conservation efforts. Information on diversity in its antimicrobial activity is also lacking. The aim of this study was to evaluate variation in antimicrobial activity of W. ugandensis leaf and stem bark extracts from different populations across the Kenyan Rift Valley. The plant materials were collected, dried at room temperature, milled into powder and sequentially extracted with dichloromethane (DCM) and methanol (MeOH). The antimicrobial activity tests against Staphylococcus aureus, Escherichia coli and Candida albicans were carried out using disk diffusion and ninety six well microtitre plate assays. Antimicrobial activities were qualitatively and quantitatively assessed by the presence or absence of inhibition zones and minimum inhibitory concentration values. The stem bark extracts displayed the highest antimicrobial activity compared to the leaf extracts, regardless of the extracting solvents. The DCM extracts exhibited stronger antimicrobial activity compared to MeOH extracts. Staphylococcus aureus and C. albicans were sensitive to the plant extracts while E. coli was resistant. This study revealed significant differences in antimicrobial activity between extracts of W. ugandensis from different plant parts and regions (P > 0.05). The knowledge on variations in antimicrobial activity is important in developing efficient conservation and utilisation strategies for the species through identification of suitable genotypes.