Antimicrobial Activity, Toxicity and Phytochemical Screening of Four Medicinal Plants Traditionally Used in Msambweni District, Kenya

Abstract

This study was designed to evaluate the antimicrobial activity, toxicity and phytochemical composition of organic and aqueous crude extracts of Zanthoxylum chalybeum Engl. (Rutaceae), Adansonia digitata L. (Bombacaceae), Launaea cornuta (Hocht. ex Oliv. & Hern) C.Jeffrey (Compositae) and Grewia trichocarpa Hochst. ex A.Rich (Tiliaceae) traditionally used by local communities of Msambweni District in Kenya.  Aqueous and organic [Chloroform: Methanol (1: 1)] crude extracts were evaluated for their in vitro antimicrobial activity against Methicillin resistant Staphylococcus aureus (MRSA), Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans using broth dilution and disc diffusion methods. Toxicity was determined using Brine-shrimp larvae (Artemia salina L. nauplii) assay. The crude extracts were screened to determine the presence of flavonoids, alkaloids, saponins and sesquiterpene lactones using standard techniques. It was observed that the organic crude extracts from all the species tested except L. cornuta exhibited dose dependent activity against B. cereus, MRSA, P. aeruginosa and C. albicans. None of the crude extracts showed any inhibition against E. coli. Adansonia digitata and Grewia trichocarpa had LC₅₀>1000 µg/ml and were shown to be non-toxic to Brine shrimp larvae unlike those of Z. chalybeum and L. cornuta which both had LC₅₀<500 ug/ml and were considered to be toxic. Phytochemical screening of the crude extracts showed that alkaloids, flavonoids, sesquiterpene lactones and saponins were present in the four plants tested.The study has shown that A. digitata and Z. chalybeum possess promising antimicrobial activity against microbes of health importance and could lead to the isolation of new and potentially effective antimicrobial compounds.

Keywords: Medicinal plants; Antimicrobial activity; Brine shrimp lethality test; Phytochemical analysis; Msambweni district; Kenya.