Antimicrobial activity and phytochemical screening of three selected medicinal plants used to treat bacterial and fungal infections in Kenya
lnfectious diseases are prevalent and Iife threatening in Kenya. The majority of the sick are seeking herbal remedies in search of effective, safe, and affordable treatments. This study investigated the antimicrobial activity and presence of alkaloids, terpenoids, sapogenins, flavonoids and quinones in different parts of Vernonia glabra, Senna didymobotrya, and Kigelia africana. Traditionally, these medicinal plants are used to treat microbial infections in Kenya. The plants were selected based on the available traditional medical knowledge and literature and collected in January 20 lOin Machakos and Kisumu counties. Diffcrent parts were dried at room temperature under shade, ground into powder and extracted in dichloromethane: methanol (1: 1) and water. The crude extracts were tested against Staphylococcus aureus (gram positive), Escherichia coli (gram negative) bacteria, Candida albicans (yeast fungus), and Aspergillus niger (filamentous fungus) for antimicrobial activity and Minimum Inhibitory Concentrations (MICs) determined using disc diffusion technique under sterile conditions. Discs impregnated with standard antibiotics (Streptomycin for bacteria and Nystatin for fungi) were used as positive controls while the extraction solvents were used as negative controls. Antimicrobial activity was determined by measuring the diameter of the clear inhibition zones around the paper discs using a transparent ruler (ern) after 24 to 48 hours for bacteria and yeast fungus, and up to 72 hours for f lamentous fungus. Thin Layer Chromatography (TLC) was used to determine the chemical compounds present in selected active crude extracts. Results showed that, organic extracts of V glabra leaf (Mean inhibition zone of 1.85 em) and flower (MIZ of 1.78 ern) recorded the highest activity against S. aureus than the standard antibiotic (Streptomycin MIZ of 1.30 em). Organic extract of V glabra flower showed significant activity only against S. aureus, with the lowest MIC of 1.5625 rng/I 00 ~I compared to streptomycin at high MIC of 6.25 mg/ 100 ul. Qual itative spray reagents on TLC plates, showed the V glabra and S. didymobotrya flavonoids highly present; terpenoids, sapogenins and quinones sufficiently present and V glabra flower alkaloids greatly present. The results of this study suggest that the three plants have significant antimicrobial properties and justify their use in traditional herbal medicine for the management of microbial based diseases. The presence of chemical compounds in most extracts of V glabra indicates its potential to produce novel compounds. Bioassay-guided fractionations are recommended to identify the compounds responsible for antimicrobial activity. Cytotoxicity assays are highly recommended for V glabra in order to verify, validate and document its safety in medicine.