ANTIMICROBIAL ACTIVITY, PHYTOCHEMICAL PROFILE AND CYTOTOXICITY OF SELECTED MEDICINAL PLANTS FOUND IN KAPTUMO DIVISION IN NANDI COUNTY, KENYA

Abstract

In Kenya, medicinal plants have been used by the local people as traditional medicine to treat different human ailments from time immemorial. The efficacy and safety of most of these plants has not been determined hence the present study conducted at Kaptumo Division in Nandi County seeks to determine to ethnobotanical survey, antimicrobial activities, profile the phytochemicals and to determine cytotoxicity of the six selected medicinal plants namely: Kigelia africana (Lam.) and Benth, Periploca linearifolia Dill & A. Rich, Ekebergia capensis Sparrm, Ehretia cymosa Thonn, Fagaropsis angolensis (Engl.) Dale and Dovyalis abyssinica (A. Rich) Warb. that are commonly used to treat infectious diseases.The ethnobotanical survey was carried out using a structured questionnaire. Fresh plants were collected from the field and air dried under shade at 25oC and later ground into powder and extracted using acetone and water. Phytochemicals from the extracts were profiled using thin layer chromatography method while in vitro cytotoxicity test was carried out following a modified rapid calorimetric assay. The extracts were tested against standard pathogenic microorganisms Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, Candida albicans ATCC 90028, Cryptococcus neoformans ATCC 32602 and clinical isolates of Methicillin resistant Staphylococcus aureus, Shigella dysentriae, Microsporum gypseum and Trychophyton mentagrophytes using disc diffusion and broth dilution methods. The solvents used for extraction were used as negative control while Fluconazole for fungi and Gentamycin for bacteria were used as positive controls. Minimum inhibitory concentrations (MIC), Minimum bactericidal concentrations (MBC) and cytotoxicity test for extracts with inhibition zone diameters of 10.0 mm and above (significance activity) were determined. All the plant extracts indicated presence of phenols, terpenoids and flavonoids. In disc diffusion assay water extracts of E. capensis were the most active and those of F. angolensis were the least against S. aureus with inhibition zone diameters of 14.7 mm and 6.0 mm, respectively. Acetone extracts of E. capensis and K. africana had a MIC of 3.125 mg/ml and 6.25 mg/ml, respectively. All the selected plant extracts were bactericidal except E. cymosa which was bacteriostatic. There was no activity at 100 mg/ml observed against fungi tested. Cell toxicity showed that most of the plant extracts tested were not cytotoxic having a CC50(μg/ml) of ≥100 against Vero cell lines except the acetone extracts of E. capensis that were moderately toxic with a CC50(μg/ml) of 12.5 , suggesting former extracts may be safe as antimicrobials. Significant variability within groups of plants, solvents and organisms at 95% confidence interval (p=0.05) was determined, and the results were found to be significant. This study enhances the validity of the medicinal plants as resources that can be relied on to provide effective and affordable healthcare to the local communities. Further research is therefore recommended to isolate, purify and characterize these chemical constituents with a view to supplementing conventional drug development especially in developing countries. The antibacterial activity of the plants under investigation demonstrated support for the claimed antimicrobial uses of the plants in the traditional medicine and provides scientific proof for their medicinal.