Efficacy of some medicinal plants used in various parts of Kenya in treating selected bacterial and fungal pathogens
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Medicinal plants have been used since time immemorial to treat and prevent human ailments. WHO indicates that up to 80% of the world’s population uses traditional medicine. Infections caused by bacteria and fungi have become a major health problem globally accounting for over 50,000 deaths every day. It is estimated that more than 70% of the pathogenic bacteria are resistant to at least one of the antibiotics commonly used to treat them. Conventional drugs are expensive and have side effects. Many plants have been used by various communities in Kenya in the treatment of bacterial and fungal infections but they have not been validated. The main aim of this study was to determine the efficacy of some medicinal plants used by various communities in Kenya that treat the selected bacterial and the selected fungal diseases in man. An ethnobotanical survey was used to select and collect plants from Mwingi North, Kisii South and Rarieda Districts based on their use to treat infectious diseases such as skin infection, diarrhea and many others. Crude extracts from Zanthoxylum chalybeum, Boscia angustifolia, Melia volkensii, Zanthoxylum gilletii, Fuerstia africana, Urtica dioica, Vernonia amygdalina, Ricinus communis, Commiphora africana, Psidia puntulata, Senna didymobotrya, Ormocarpum trichocarpum, Sesbania sesban, Balanites aegyptiaca, Albizia coriaria, Ficus sycomorus, Rhus natalensis and Tamarindus indica believed to contain secondary metabolites were screened against ten microorganisms, including the bacteria:- Salmonella typhi ATCC 19430, Escherichia coli ATCC 25922, Bacillus subtilis, Staphylococcus aureus ATCC 25923 and Methicillin Resistant Staphylococcus aureus. The fungal strains that were used are; Aspergillus niger, Candida albicans ATCC 90028, Microsporum gypseum, Crytococcus neoformans ATCC 18310 and Trichophyton mentagrophyte. The plants were screened using Kirby Bauer disc diffusion method. Phytochemical screening was carried out to identify the presence or absence of classes of bioactive compounds. Data was analyzed using one way ANOVA, significant means were separated using Tukey’s test. Generally, Fuerstia africana, Zanthoxylum chalybeum, Balanites aegyptiaca, Ormocarpum trichocarpum, Senna didymobotrya and Tamarindus indica gave strong antibacterial results of between 14.5 mm and 20 mm as Albizia coriaria, Ficus sycomorus, Commiphora africana Rhus, natalensis Senna didymobotrya, Psidia puntulata, and Tamarindus indica produced strong antifungal results of between 15.5 mm and 20.5 mm. The results of MICs and the MBCs/MFCs of the extracts of Albizia coriaria, Ficus sycomorus, Senna didymobotrya, Psidia puntulata, Fuerstia africana, Balanites aegyptiaca and Tamarindus indica showed a good activity of 0.9375 mg/ml in some test cultures. Salmonella typhi ATCC 19430 and Escherichia coli ATCC 25922 were the least sensitive bacteria while Candida albicans ATCC 90028 was the least sensitive fungus. The present study indicates that the majority of the plants tested are an important source of antibacterial agents especially on Gram positive bacteria (Staphylococcus aureus, Bacillus subtilis and Methicillin Resistant Staphylococcus aureus) and antifungal agents against the dermatophytes especially Microsporum gypseum. This study recommends that the plant extracts with good antimicrobial activity be subjected to both pharmacological and toxicological studies.