In-Vitro antimicrobial activity and toxicity of selected medicinal plants from Kirinyaga and Machakos counties, Kenya

Abstract

Introduction: Herbal drugs are increasingly gaining popularity over conventional drugs all over the world as they are more affordable than conventional medicines and easily accessible to the communities in rural areas. In addition, challenges of conventional medicines, such as increased drug resistance, have increased the preference for herbal drugs. Despite their increased usage, scientific research on the efficacy and toxicity of some of these herbal drugs is insufficient. The present study aimed to screen the phytochemical constituents, antimicrobial activity, and cytotoxicity of three Kenyan medicinal plants, namely Colocasia esculenta, Commiphora africana, and Caesalpinia volkensii. Method. Antimicrobial activity was evaluated using both disc diffusion and agar well diffusion techniques, while cytotoxicity was determined by the brine shrimp lethality test. Five microorganisms, namely Escherichia coli, Staphylococcus aureus, Bacilus subtilis, Candida albicans, and Aspergillus niger were used. Amoxicillin and Fluconazole served as the positive control, while Dimethyl sulphoxide served as the negative control. Results. Anthraquinones, flavonoids, tannins, saponins, terpenoids, and alkaloid compounds were found after screening. Toxicity screening showed that Colocasia esculenta had an LD50 of 1438.826, that of Commiphora africana was 4432.437, while those of Caesalpinia volkensii leaves and bark were 1808.984 and 1958.079 respectively. The plants were active against all the microorganisms, except A. niger. E. coli was most susceptible to Caesalpinia volkensii leaves extracts (p=0.000), with an inhibitory length of 1.4333cm. C. albicans was most susceptible to Colocasia esculenta extracts (p=0.000) with an inhibition zone of 0.8667cm. Conclusion. All the plants exhibited antimicrobial activity and were non-toxic (LD50? 1000µg/ml).