Abstract:
Plants are capable of synthesizing various chemical compounds that support them to defend against attack from an immense diversity of predators such as fungi, bacteria, insects and herbivorous mammals. Although some of these chemical compounds are toxic to plant predators, they seem to be effective drugs for human diseases. Psidium guajava L. is used to treat some diseases such as diarrhea, diabetes, gastric cancers, osteoarthritis and skin diseases and this plant belongs to the family Myrtaceae. The aim of this study was to identify the phytochemical constituents and to determine the antifungal and antibacterial activities of Psidium guajava leaf extracts from dry zone and wet zone of Sri Lanka. The antifungal bioassay was performed by Agar well diffusion method with the concentration of 500 ppm of the leaf extracts against the fungi Aspergillus sp., Fusarium sp., Penicillium sp., Rhizopus sp. and Trichoderma sp. The antibacterial bioassay was performed against the bacteria Acinetobacter sp., Bacillus sp., Escherichia coli, Pseudomonas sp., and Staphylococcus sp. Methanol and acetone extracts of leaves of P. guajava displayed high degree of antifungal activity (mean diameter) for both dry and wet zones against Aspergillus sp. (20.8 mm, 18.5 mm, 23.0 mm and 20.3 mm) and Trichoderma sp. (16.3 mm, 20.3 mm, 20.3 mm and 22.5 mm) respectively. Methanol and acetone extracts of leaves of P. guajava revealed high degree of antibacterial activity for wet zone against Bacillus sp. (26.0 mm, 27.1 mm) and Acinetobacter sp. (20.0 mm, 23.0 mm) respectively. The phytochemical analysis revealed that the leaves of P. guajava from both zones contain secondary metabolites alkaloids, flavonoids, saponins, tannins, coumarins and cardiac glycosides which are the bioactive compounds and could play major role in antimicrobial activities.
