Screening of antidiarrhoea medicinal plants for invitro antimicrobial activity against clinical and environmental enteropathogens

Abstract

Plants in traditional medicine have been widely used to treat diarrhoea diseases in Kenya. Ethnobotanical surveys are useful in the identification and selection of medicinal plants with potential therapeutic values. Since no ethnobotanical study has been conducted in Rachuonyo district of Nyanza province to identify the plants commonly used for the treatment of diarrhoea, this study interviewed 191 respondents and found that Terminalia brownii Fres. (barks), Melia volkensii Guerke (barks), Melia volkensii Guerke (leaves), Aloe secundiflora Engl. and Albizia coriaria Welw. ex Oliv. (barks) were most frequently used. The plants were collected and extracted using hexane, methanol, acetone and water and tested against clinical and environmental enteric pathogens. Phytochemical tests indicated that the plants contained tannins, triterpenoids, flavonoids, steroids, alkaloids, glycosides, phenols and saponins in varying amounts. The antimicrobial assay of the plant extracts showed that the highest (24 mm zone of inhibition) activity was by methanol extracts of Terminalia brownii barks against Vibrio cholerae (clinical isolate) while acetone extracts of Melia volkensii leaves had the least activity (7 mm) against Shigella dysenteriae (clinical isolate). The extracts were active at relatively low concentrations, with their minimum inhibitory concentrations ranging from 3.13 mg/ml for Melia volkensii bark against Shigella dysenteriae to 50 mg/ml for Albizia coriaria bark against E.coli ATCC 25922. However, some of the plant extracts (Aloe secundiflora) were inactive against xv some of the test isolates, indicating that not all prescribed antidiarrhoeal plants may be effective against enteric pathogens. The present study showed synergism between ampicillin, cefuroxime, gentamicin and cotrimoxazole with all plant extracts tested at various concentrations against some antibiotic-resistant bacteria (V. cholerae, S. dysenteriae, Enterobacter aerogenes, Proteus mirabilis, Pseudomonas aeruginosa and Escherichia coli). This indicates that the use of plant extracts together with antibiotics may enhance activity against drug-resistant pathogens. In the kill kinetics tests, the extracts of Terminalia brownii were bactericidal against Staphylococcus aureus while Melia volkensii and Albizia coriaria were bactericidal against Escherichia coli. This is interesting because S. aureus has been known to be therapeutically problematic especially in immunocompromised people. Hence, Terminalia brownii can be used in treating S. aureus infections in this group of people. The brine shrimp lethality tests revealed that the plants were of low toxicity and can be used for the treatment of diarrhoea diseases in humans and avoid possible detrimental health risks. The overall results of the present study authenticate the therapeutic values of the antidiarrhoeal medicinal plants and show that they can be used in further drug development.