In vitro Antibacterial Activity of Aqueous Extracts of Cashew (Anacardium occidentale L.) Fruit Peels Using Bioautography Method

Aims: Bark, leaves and gum of cashew (Anacardium occidentale L.) have been reported to be effective in curtailing the growing problems of resistance of bacterial pathogens. The in vitro activity of aqueous extracts of cashew apple peels was determined in this study against two clinically important pathogens.

Place and Duration of Study: The work was conducted at the Department of Microbiology, Ekiti State University, Ado-Ekiti, Nigeria and processed immediately. This study was carried out between June, 2009 and January, 2010.

Methodology: Bioautographic method was used to test the antibacterial activity of aqueous (cold and hot water) extracts of cashew apple peels on Escherichia coli O157:H7 and methicillin-resistant Staphylococcus aureus (MRSA). The zones of inhibition of the extracts were compared.

Results: The activity of the fifth hour hot water extract was highest with zones of inhibition of 415.48 and 346.30 sq. mm against E. coli O157:H7 and MRSA respectively. E. coli O157:H7 was more susceptible to the extract with the zone of inhibition ranging between 176.79 and 283.53 sq. mm while that of MRSA was153.94 - 346.30 sq. mm. The 5 h extract of cold water was more potent on the test organisms with 615.75 and 490.87 sq. mm diameters of inhibition on E. coli O157:H7 and MRSA respectively. Cold water extracts produced more active compounds (13 biologically active spots) that inhibited the growth of the test organisms than the hot water extracts, with six spots.

Conclusion: The extracts of the peels of the cashew apple against the test organisms are promising. However, the nature and mechanisms of action of the biologically active compounds in the extracts are still open to investigation.