Antimicrobial effects of psidium guajava extract as one mechanism of its antidiarrhoeal action

Abstract

A morphine-like spasmolytic action (not naloxone reversible; involving the inhibition of acetylcholine release) and also effects on the transmural transport of electrolytes (Na(+) and K(+)) and water have been reported as possible modes of the antidiarrhoeal action of polar fractions of Psidium guajava leaf extractives. The objective for this study was to verify if the reported modes of the antidiarrhoeal action should be broadened to include direct antimicrobial actions on some of the more common bacteria known to cause toxin-induced acute diarrhoea. Serial dilutions of a water-soluble, freeze-dried methanolic extract were tested on 10 such organisms, grown separately on nutrient agar plates, to determine the minimum inhibitory concentration (MIC) for each of these bacteria. These included the causative agents for (i) enteric fever (Salmonella typhi, Salmonella paratyphi A, Salmonella paratyphi B and Salmonella paratyphi C), (ii) food poisoning (Salmonella typhimurium and Staphylococcus aureus), (iii) dysentery (Shigella dysenteriae, Shigella flexneri and Shigella sonnei), and (iv) cholera (Vibrio cholerae). The growth of all these organisms was inhibited at the MIC of 10mg/ml of the extract, which is equivalent to 2.5μg/ml of active extractable flavonoids. The most sensitive organisms (MIC = 1mg/ml) were Staphylococcus aureus, Vibrio cholerae and Shigella flexneri.

Keywords: Psidium guajava extract; antimicrobial effects; bacterial toxin-induced diarrhoea.

Fig. 1:

Mean growth inhibitions (diameters of inhibition zones) in mm produced by 20 mg/ml (equivalent to 5μg/ml of the active compound) of Psidium guajava extract on 10 common diarrhoea-causing bacteria

Fig. 2:

Mean growth inhibitions (diameters of inhibition zones) in mm produced by 1 mg/ml extract (MIC) of Psidium guajava on the 3 most sensitive of the 10 common diarrhoea-causing bacteria. The MIC for the other 7 organisms was 10 mg/ml (equivalent to 2.5 μg/ml of the active compound) of Psidium guajava extract