In Vitro Antibacterial Activities of Dichloromethane: Methanol Extracts of Fuerstia Africana, Polygala Sphenoptera and Centella Asiatica Against Selected Bacteria
Sieberi, Berick Moturi
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Bacterial infections are responsible for numerous deaths every year worldwide. On average, 80% of the African populations cannot afford conventional drugs. Moreover, many synthetic antibiotics are associated with side effects and progressive increase in antimicrobial resistance. Currently, there is growing interest in discovering new antibacterial agents from medicinal plants. About 60% of the population living in developing countries depends on herbal remedies for healthcare needs. This study involved screening of three medicinal plants commonly used by herbal medicine practitioners in Kisii county to treat symptoms which may be related to bacterial infections. Null hypotheses of the study were, dichloromethane: methanol extracts of Fuerstia africana, Polygala sphenoptera, and Centella asiatica have no therapeutic phytochemical constituents, dichloromethane: methanol extracts of Fuerstia africana, Polygala sphenoptera, and Centella asiatica have no in vitro antibacterial activities against selected bacteria and dichloromethane: methanol extracts of Fuerstia africana, Polygala sphenoptera, and Centella asiatica have no time kill kinetic activities against selected bacteria The Standard in vitro bioassay methods were applied throughout this study. They involved preliminary screening against human pathogenic bacteria strains using agar disc diffusion, broth micro-dilution and time kill kinetics methods with tetracycline as a positive control. Phytochemical screening was carried out to determine the presence of different classes of compounds in the crude extracts. Dichloromethane: methanol extracts of Fuerstia africana, Polygala sphenoptera and Centella asiatica were screened against five human pathogenic bacteria strains Salmonella typhi ATCC 19430, Escherichia coli ATCC 25922, Shigella sonnei ATCC 25931, Bacillus subtilis ATCC 21332 and Staphylococcus aureus ATCC 25923. Data was analyzed using one way ANOVA, Tukey’s post hoc test. The extracts showed strong antibacterial activities. The results of minimum inhibitory concentrations and minimum bactericidal concentrations of the extracts showed high activities of between 15.63 and 31.25 mg/ml in some test cultures. However, Bacillus subtilis ATCC 21332 and Staphylococcus aureus ATCC 25923 were least sensitive. Time kill kinetics studies of the extracts showed dose and time dependent kinetics of antibacterial properties. Phytochemical screening of extracts showed the presence of alkaloids, flavonoids, phenolics, terpenoids, cardiac glycosides, saponins, steroids, and tannins. The present study indicates that the tested plants may be an important source of antibacterial agents and recommends that the active phytoconstituents be isolated, identified and screened individually and in different blends for activities and also subjected to further research for in vivo and toxicological studies.