Phytochemical screening and antibacterial testing of selected Namibian medicinal plants against laboratory and clinical bacteria that cause Diarrhoea
Medicinal plants are rich in a wide variety of bioactive compounds associated with various ailments; including antibacterial activity and some of them have been used worldwide in traditional settings to treat diarrheal diseases. However evidence on safety and efficacy of some of these traditional medicinal plants is lacking, preventing their mainstream use. This study aimed at determining the antibacterial activity of Boscia albitrunca, Ziziphus mucronata, Combretum apiculatum, Solanum linnaeanum and Terminalia sericea against clinical and laboratory diarrheal pathogens and screen selected plants for the presence of major phytochemical compound. Plant parts (bark, roots and twig) were collected from Kunene region and extracted using aqueous and organic solvents and screened for the presence of triterpenoids, saponins, flavonoids, steroids, coumarins, tannins and alkaloids by thin layer chromatography (TLC). Antibacterial activities of the organic and aqueous extracts were determined against laboratory strains of Escherichia coli, Shigella bodyii, Staphylococcus aureus and Listeria monocytogenes and clinical strains of Salmonella, E. coli and Shigella, by disc diffusion method at three different concentrations (250, 500 and 1000 μg/ml). The average inhibition zones were determined on Mueller- Hinton agar plates. Phytochemical screening revealed higher presence of antibacterial compounds triterpenoids, saponins, flavonoids, steroids, coumarins and alkaloids in organic extracts and tannins in aqueous extracts. The organic extracts of T. sericea showed broad spectrum antibacterial activity against both clinical and laboratory diarrheal pathogens. The highest antibacterial activities at the lowest concentration were observed from organic extracts of S. linnaeanum against laboratory L. monocytogenes (15.5± mm, n=3) and C. apiculatum against clinical Salmonella (12 ± mm, n=3) at 250 μg/ml. In aqueous extracts, C. apiculatum showed stronger antibacterial activity against clinical Shigella (12 ± mm, n=3) and T. sericea against laboratory strains of E. coli and Listeria monocytogenes (9 ± mm, n=3) at 500 μg/ml. Ampicillin showed antibacterial activity against laboratory strains of S. boydii and S. typhi however it showed no antibacterial activities against clinical strains of Shigella and Salmonella. Organic extracts of T. sericea and C. apiculatum also showed a lowest Minimum inhibitory concentration (MIC) of 250 μg/ml against E. coli and Salmonella respectively. Minimum inhibitory concentration of 62.5 μg/ml was recorded for T. sericea and C. apiculatum organic extracts against laboratory strains of S. aureus and E. coli respectively. Organic extracts of T. sericea and C. apiculatum showed an MIC of 250 μg/ml against clinical E. coli and Salmonella respectively. The study confirmed the possibility of using these plant extracts to develop alternative medicine to treat diarrheal pathogens.
Phytochemical screening, Antibacterial testing, Diarrhoea
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