Antibacterial Effects of Thyme, Savory, Rosemary, Mint and Peppermint Essential Oils on Five Gram-positive Bacteria in Comparison with Effects of Three Antibiotics on the Bacteria

Background and Objectives: To investigate antibacterial activity of various volumes of five natural Lamiaceae plant essential oils on five Gram-positive bacteria, compared to those of three antibiotics on these bacteria.  Materials & Methods: In this study, disk diffusion method was used and inhibition zone diameters of 10, 15 and 20 microliters of thyme, savory, rosemary, pennyroyal and spearmint essential oils against Bacillus cereus and Enterococcus faecium, Listeria monocytogenes, Staphylococcus aureus and Enterococcus faecalis were recorded. Chemical compositions of the essential oils were analyzed using gas chromatography. Results: Inhibitory effects of the essential oils increased significantly with increasing their volumes, enhancing the bacterial growth inhibition zone. Thyme and savory significantly decreased the bacterial growth, compared antibiotics. Rosemary, mint and peppermint included smaller diameters of growth inhibition zones, compared to essential oils, with no significant differences at 20 μl, compared to antibiotics. Conclusion: Results have shown that thyme and savory include great inhibitory effects on growth rates of food bacteria. In fact, 20 microliters of these herbals increase the shelf life of foods with great inhibitory effects. Comparison of the effects of antibiotics and essential oils has demonstrated that savory includes the greatest inhibitory effect on Enterococcus and thyme on Bacillus cereus, Listeria monocytogenes and Staphylococcus aureus.