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.
