Antibiotics are quite prevalent in modern society and present in many products humans use on a day-to-day basis. However, the general increase in the strength of antibiotics over the past decades has led to a similar coevolution in bacteria who grow more and more resistant to the stronger antibiotics humans are using. Essential oils are aromatic compounds produced by plants that naturally have antibiotic properties. In the past, these oils were often used for antiseptic or anesthetic purposes, but the rise in modern medicine has lessened their usage. The purpose of this project is to provide an in depth analysis of the antibiotic properties of various essential oils and their chemical components which can shed light on their potential for mainstream usage.

To test the antibiotic effectiveness of the essential oils, the disk diffusion test was conducted on Mueller-Hinton agar petri dishes. Cinnamon, thyme, oregano, and tea tree oil were tested at 10%, 25%, 50%, and 100% concentrations on E. coli, M. luteus, and B. subtilis. A positive control, iodine tincture, was used for comparison purposes and the negative control on the solvent, ethanol, was used to ensure the essential oils were the substances with the antibiotic properties. To determine the relative concentration of bacteria present on certain plates, a standard curve was created using absorption spectroscopy and referenced for experimental plates. To learn about the potential for essential oils to be incorporated into products such as plastics, a heat test was conducted on the cinnamon essential oil to determine its efficacy even after being heated to 100°C, 130°C, and 175°C.

The disk diffusion test showed that on average, the essential oils were more effective on the gram-positive strains of bacteria (M. luteus and B. subtilis) and less effective on the gram-negative strain (E. coli). However, even at concentrations as low as 10% for bacteria like B. subtilis, the essential oil was found to be more effective than iodine tincture. In most trials though, the 25% concentration was equal to or better than the iodine tincture in terms of antibiotic effectiveness. The absorption spectroscopy test found that on plates with thyme and oregano oils at 50% or 100% concentration, the relative concentration of bacteria was less than 25%, indicating a dispersive inhibiting effect of these oils. Analysis of the data produced by the heat test showed that there was no statistically significant difference between the results of the experimental trials and the control of 37°C.

This project was able to conclude that all the tested essential oils have significant antibiotic properties and at some concentration, are more effective than iodine tincture. Thus, they could be used as antiseptics. Finally, the heat test was able to conclude that heating of the cinnamon essential oil does not cause a decrease in its efficacy, an important property if the oils were to be infused into plastics or incorporated into other products.