A study into the antimicrobial effects of cloves (Syzgium aromaticum) and cinnamon (Cinnamomum zeylanicum) using disc-diffusion assay

Purpose - This paper is aimed at food science or biology students planning a practical independent study into the antimicrobial properties of spices and academic staff wishing to develop a straightforward and reproducible practical activity. Design/methodology/approach - Disc-diffusion assays are used to investigate the antimicrobial activity of cinnamon and cloves against two bacteria Escherichia coli B and staphylococcus albus and a yeast Saccharomyces cerevisiae. Aqueous and alcoholic extracts of the spices and alcoholic extracts of their essential oils are examined. Minimum inhibitory concentrations of alcoholic extracts of both spices and oils are also determined. Findings - Both spices demonstrated microbial inhibitory effects; alcoholic extracts had greater activity than aqueous extracts. Additionally, essential oils had greater activity than the spices. Minimum inhibitory concentrations were smaller with the oils than with the spices. Research limitations/implications - Although the research for this paper involved just two spices, such is the size of the plant kingdom that there are wide opportunities for further investigations using this procedure. Practical implications - Disc-assays were found to be a simple, cheap and reproducible practical method. For this paper, micro-organisms available for educational purposes were used; however, other organisms could be investigated depending upon available microbiological expertise and facilities. Originality/value - The results demonstrate that the antimicrobial effects of spices and particularly their essential oils can be examined using disc-diffusion assay. The method provides many opportunities for student investigation.