In vitro antibacterial activities and safety of aqueous extract of selected kenyan medicinal plants against diarrhea causing bacteria
Mugweru, Francis Gitau
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Diarrheal diseases constitute a major public health problem, particularly in the developing world, where mortality and morbidity rates are still very high. Acute diarrhea is a common cause of death in developing countries and second most common cause of infant deaths worldwide. Diarrhea is a very common complication of infection with the HIV and often leads to wasting and malnutrition. In developing countries, up to 80% of children and 90% of adults with HIV infection develop diarrhea. Many of the antibiotics used in management of diarrhea caused by bacteria are experiencing increased resistance posing a great public health concern. This calls for the need to continue searching for new drugs to control this condition. In this study, aqueous extracts of five selected medicinal plants were investigated for antibacterial activity against diarrhea causing bacteria pathogens (Salmonella spp., Campylobacter spp., Shigella spp., Diarrheagenic E. coli, Pseudomonas aeruginosa, and Proteus spp.). The clinical isolates and standard organisms were obtained from reliable laboratories of KEMRI and KNH. Identities of the micro-organisms were confirmed by colonial morphology, gram staining and biochemical test. The plants were collected within Kenya from their ecological zones. They were selected from among medicinal plants used in the treatment of various ailments using the information obtained from ethno-medical practices and literature. Aqueous extraction and freeze drying was employed in preparation of plant extracts. Disc diffusion technique was used for preliminary determination of in vitro antibacterial activity of the extract by evaluating the ability to inhibit the growth of the bacterial species. Three out of the five selected medicinal plants extracts tested by disk diffusion technique had inhibitory activity on most bacterial isolates with inhibition diameter ranging from 9mm to 18mm. These are Senna spectabilis (Leaves), Maytenus putterlickioides (Roots) and Olinia usambarensis (leaves). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts with the most prominent activity were evaluated by plate dilution method. The efficacy and potency of the extracts were assessed by comparing the MIC and MBC values of the five bacterial species to the selected medicinal plant extract with those of chloramphenicol. A regression analysis was used to analyze mean MIC and MBC for each of the selected organisms. All the extracts exhibited an MBC range of 12.5 to 75mg/ml that was greater than MIC range of 6.25 to 50mg/ml, which indicates a bacteriostatic activity. This was similar to chloramphenicol, suggesting the mode of action may be closely related. In vivo toxicity of the plant extracts was assessed using mice model. The reduced growth rate, increased the percent relative organ to body weights and increased levels of some serum parameters in mice treated with plant extracts (S. spectabilis and O. usambarensis) relative to that of control indicates some toxic effects. This study will enhance understanding of efficacy and safety of ethno-medical materials in the management of diarrhea caused by bacterial pathogens. It will also promote possible scientific development of antibacterial agents from these plants.