Background:The guava, Psidium guajava is one of the most gregarious of fruit trees, of the Myrtaceae family. The leaf of P. guajava is a common herb used in the treatment of diarrhea in Nigeria and this has generated special interest in the probable antimicrobial and genotoxic effects of the leaf. However the mode of action of the leaf extracts has not been reported, hence the genotoxicity study. Material and Methods: Antimicrobial activity of the aqueous and ethanolic extracts of the leaves of Psidium guajava on Aspergillus fumigatus, Candida albicans, Salmonella spp., and Staphylococcus aureus were investigated using agar-well method and also subjected to phytochemical screening and Gas chromatography-Mass spectroscopy analysis. General toxicity and genotoxic effects of the aqueous leaf extracts (0.01 g/mL, 0.03 g/mL, 0.06 g/mL and 0.08 g/mL) of P. guajava on Allium cepa root tips were also investigated using aceto-orcein squash technique. Results: Results showed that both aqueous and ethanolic extracts of guava leaf inhibited the growth of the bacteria and fungi tested. The ethanolic extract showed stronger inhibition than the aqueous extract against the organisms. A total of forty one compounds were identified in guava leaves using GC-MS analysis and these substances were found to be essential oils. The cytological effects at low concentration included mainly c-mitosis, vagrant chromosomes, chromosome bridges, and binucleate cells with EC 50 of 0.02 g/mL. Conclusions: The antimicrobial activity of the essential oils from the extracts of leaves of P. guajava could be partly due to alterations associated with the cell division as deduced from the results. Ofodile NL, Nwakanma NMC, Mordi M, Ademolu O, Ezimoke I, Owoso J (2013) Genotoxic and antimicrobial studies of the leaves of Psidium guajava. Eurasia J Biosci 7: 60-68. http://dx.

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