Evaluation of antimicrobial activity, toxicity and phytochemical screening of selected medicinal plants of losho, narok county, Kenya.
In Kenya, microbial infections are a major cause of morbidity. Antibiotic effectiveness is threatened by increasing resistance of pathogenic microbes against most available drugs as new pathogens continue to emerge. Currently, herbal remedies offer hope considering they are readily and cheaply available. The objective of this study was to investigate antimicrobial activity, brine shrimp lethality and phytochemical composition of crude extracts of four selected plants namely Schrebera alata (Oleaceae), Ormocarpum kirkii (Papilionoideae), Helichrysum forskahlii (Asteraceae) and Cussonia holstii (Araliaceae) that are medicinally used by herbalists from Losho, Narok County Kenya for treatment of ear, nose and throat infections, gastrointestinal disorders and skin ailments. Qualitative antimicrobial susceptibility test against five microorganisms, methicillin resistant Staphylococcus aureus, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans was investigated using agar diffusion methods to generate inhibition zones and data accrued analyzed using Analysis of variance. Minimum inhibitory concentrations were determined by broth microdilution method. Toxicity of the extracts was investigated using brine shrimp lethality assay. Median lethal concentration fifty was determined by analysis of data using Finney‟s computer program. Phytochemical screening for flavanoids, sterols, alkaloids, tannins, quinones and terpenoids and saponins was determined using standard procedures. It was observed that the organic crude extracts of H. forskahlii had the highest inhibition zone against methicillin resistant Staphylococcus aureus of 19.5 and 18.5 mm in agar well and agar disk diffusion respectively. In addition, organic extracts of H. forskahlii revealed the highest antifungal inhibition zone of 8.5 mm in agar well diffusion. Minimum inhibitory concentrations values varied from 15.625 to 250mg/ml.Organic crude extracts of Helichrysum forskahlii and Cussonia holstii were found to be highly toxic with lethal concentration of 0.009 mg/ml. All the plant crude extracts contained flavanoids, sterols, alkaloids, tannins, quinones and terpenoids. Saponins were present in all the plant extracts screened except organic extracts of H. forskahlii. This study provides the first record of antimicrobial activity, toxicity and phytochemical composition of S.alata and C.holstii. The study has shown that H. forskahlii and O.kirkii possess promising antimicrobial activity against microbes of health importance and could lead to the isolation of novel, safe and efficacious xii antimicrobial compounds. Further research should be carried on O. kirkii and S. alata to isolate and characterize the compounds responsible for the observed activity. Key words: Medicinal plants; Antimicrobial activity; Brine shrimp lethality assay; phytochemical composition; Losho; Narok County; Kenya.