The Antibiotic Activity of Tea Tree, Eucalyptus, and Cinnamon Bark Oils

Abstract

The emergence of antibiotic resistant bacteria is of pressing concern, especially given that the pharmaceutical industry has decreased funding for infectious disease drug discovery programs. It is estimated that over 2 million people are infected with antibiotic resistant strains of bacteria each year, resulting in over 23,000 deaths. Researchers are currently looking for novel antibiotics in alternative sources. Essential oils, derived from plants, are an ancient homeopathic remedy that are traditionally known to have antimicrobial properties. Therefore, several essential oils were examined in search of novel antibiotics. Tea tree (Melaleuca alternifela), eucalyptus (Eucalyptus globulus), and cinnamon bark (Cinnamomum cassia Blume) oils showed antibiotic activity in Kirby‐Bauer disk diffusion assays. The Minimum Inhibitory Concentration (MIC) values for tea tree, eucalyptus, and cinnamon bark oils were determined to be 1.25%, 0.313%, and 0.0391%, respectively. All three oils proved effective against both Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli. Cinnamon bark oil was the most effective and was further characterized. Cinnamon bark oil retained its MIC in the presence of 10% human serum protein, indicating that it does not interact with proteins in the bloodstream. Cinnamon bark oil showed bactericidal activity in a time kill assay. To determine the active component within cinnamon bark oil, an analysis of its constituents was conducted. Three of the main components of cinnamon bark oil, trans‐cinnamaldehyde, cinnamyl cinnamate, and benzyl cinnamate, were subjected to preliminary testing via Kirby‐Bauer disk diffusion tests. Trans‐cinnamaldehyde appeared to be the only effective component against both S. aureus and E. coli. Results suggest that cinnamon bark oil may contain a promising novel antibiotic.Support or Funding InformationThis research was supported by Grand Valley State University's Student Summer Scholars program.