Antimicrobial activity, acute toxicity and phytochemical composition of four medicinal plants traditionally used in Sotik sub- county, Kenya

Abstract

In Kenya, microbial diseases are prevalent and life threatening. Currently, herbal remedies are of interest as considered to be easily available, safe, effective and affordable. This study was designed to investigate antimicrobial activity, toxicity and phytochemical composotion in crude extracts of Leucas calostachys, Mimusops kummel, Acacia lahai and Caesalpinia decapetala. These plants are majorly used by herbalist from Sotik Sub- County, Kenya for treatment of gastroinstestinal problems. Antimicrobial activity was investigated using disc diffusion method and data analyzed using ANOVA. Minimum inhibitory concentrations (MIC) were determined by broth dilution method. Microorganisms employed were methicillin resistant Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Extracts toxicity was investigated using brine shrimp lethality assay, LD-50 was determined by analysis of data using Finney’s computer program. Phytochemical screening for flavonoids, alkaloids, saponins and sesquiterpene lactones was determined using Thin layer Chromatography (TLC). Highest antibacterial activity was noted with methanol extract of A. lahai on B. cereus while acetone extracts of A. lahai exhibited the highest antifungal activity. Most active crude extracts had MICS values of 20mg/ml. All the tested extracts had LC50 values greater than 1000 μg/ml hence non-toxic on Artemia salina larvae. Flavonoids, alkaloids and saponins were present in all the plant species tested. Sesquiterpene lactones were present in L.calostachy and M. kummel. The results of this study shows that the tested plants have antimicrobial effects and is non-toxic supporting their traditional usage for treatment of microbial infections. Further bioassay of isolated compounds from active crude extracts is recommended. Key words: Antimicrobial activity, Brine shrimp lethality assay, Medicinal plants, Phytochemical composition, Sotik Sub- County; Kenya.