The mechanisms by which the ethanolic extract of the leaves of Psidium guajava
exerts its antidiarrhoeal effect were investigated. Antimicrobial analyses of the extracts were carried out using standard cultures of Escherichia coli
(ATCC 15597) and Staphylococcus aureus
(ATCC 6538). There was a concentration dependent inhibition of growth that was less significant for S. aureus
(p < 001). Zones of inhibition remained clear without bacterial regrowth even after 72 hours. Diarrhea was induced with castor oil (10ml/kg body weight) in different groups of Wister albino rats (A -E) and treated per os with normal saline for the positive control (1ml/kg body weight); extract (40 mg/kg body weight); extract (80 mg/kg body weight), loperamide as standard drug (10 mg/kg body weight); gum acacia (10 mg/kg body weight) respectively. Group F which received no treatment served as the negative control. Results showed that the inhibition of diarrhea, measured as percentage faecal output relative to the positive control, was dose -dependent and comparable to the standard drug. The plant extract also showed a reduction in gastrointestinal motility, measured as the distance traveled by the charcoal plug in the small intestine. This was non - significantly different from the standard drug, loperamide (p < 0.05). The leaf of P. guajava
therefore exerted its antidiarrhoeal effect by a dual action of its antimicrobial effect and reduction in gastrointestinal motility.