Essential oils have long been recognized for their medicinal and antimicrobial properties. The use of essential oils date back to ancient Egypt. During the time of the “Great Plague” essential oils were used to fumigate spaces and were found to protect individuals exposed to the plague. The pleasant smell that plants give off can be captured and are known as terpenes which are evaporative, lipid-loving liquid substances found in essential oils. Plants make these substances as a survival mechanism against environmental stressors including pathogens. Today, essential oils are used to treat a wide array of medical conditions from cancer, pain and stress to infectious disease. Our goal is to expand the current knowledge of essential oils for practical application in the medical field.
Much of the current laboratory research in essential oils does not account for the lipid-loving nature of essential oils or mimic how essential oils are most safely used, in its vaporized state. When using a diffuser, microorganisms are coming into contact with the essential oils in its vaporized state rather than direct contact. The most common method for testing uses Minimum Inhibitory Assays which are most comparable to direct contact or topical application. To more closely emulate how aromatic essential oils would be used at home in a diffuser, we constructed a new and unique experimental design. This was accomplished by using custom made glass cups placed in the center of a petri dish inoculated with a microorganism of interest.
Nineteen different essential oils were tested against 10 different microbes in a blanket study assessing for essential oil antimicrobial activity. Of these microbes, four were gram positive, three were gram negative and one was a fungus. Two of these were also antibiotic resistant. The essential oils tested were: Melaleuca alternifolia (tea tree), Origanum vulgare (oregano), Eugenia caryophyllata (clove), Rosmarinus officinalis (rosemary), Lavandula angustifolia (lavender), Cinnamomum zeylanicum (cinnamon), Boswellia (frankincense), Citrus limon (lemon), Thymus vulgaris (thyme), Mentha piperita (peppermint), Abies alba (white fir), Juniperus virginiana (cedarwood), Thuja plicata (arborvitae), Gaultheria fragrantissima (wintergreen), Foenicilum vulgare (fennel), Cananga odorata (ylang ylang), Cinnamomum cassia (cassia), Citrus sinensis (wild orange) and Cymbopogon flexuous (lemon grass). The microbes tested were selected for their relationship to dermatological and respiratory infections. Streptococcus pyogenes is commonly known to cause pharyngitis and necrotizing fasciitis. Staphylococcus aureus is one of our bodies commensal bacterias than can over grow and become pathogenic causing impetigo and folliculitis. Staphylococcus epidermidis is another one of our commensal bacteria that is problematic in nosocomial infections and surgical wounds. Mycobacterium smegmatis is a laboratory safe version of the bacteria that causes tuberculosis. Pseudomonas aeruginosa is commonly found in community acquired pneumonia, whirlpool folliculitis, cystic fibrosis, nosocomial infections, infections related to immunocompromised patients and burns. Bordetella bronchiseptica is known to cause kennel cough and is closely related to Bordetella pertussis, which causes whooping cough. Klebsiella pneumoniae is commonly found in respiratory, skin and soft tissue infections. Candida albicans causes candidiasis.
As part of the preliminary research to determine the experimental design, cinnamon was tested against Pseudomonas aeruginosa in a Minimum Inhibitory Concentration (MIC) assay similar to how most of the current literature is conducted. Cinnamon killed pseudomonas at 0.1 μL which is a small fraction of one drop of essential oil. In our aromatic assay, our highest tested concentration of cinnamon, 160 μL, showed negligible activity against pseudomonas. Since essential oils are typically used with an aromatic application, an aromatic approach in essential oil research is important to have clinically useful data. Pseudomonas aeruginosa is overall great bacteria to research. It has extraordinary capabilities to resist antibacterial treatment because of its ability to rapidly adapt. With Pseudomonas aeruginosa being highly susceptible to the MIC assay, further research would be warranted to explore its susceptibility to osmotic variance.
Also as part of the preliminary research, two commercially available and reputable sources of two different essential oils were compared for lavender and tea tree essential oils for all 10 different microorganism. For lavender, both manufacturers used the same plant parts for essential oil extraction. Both of these essential oils had similar antimicrobial activity against the same bacteria. For tea tree oil, there were inconsistencies in its activity level between manufacturers against various microorganisms. This was likely related to the manufacturers using different plant parts to extract their essential oils. As with all botanical products, the plant part used is important in determining their therapeutic value.
Mycobacterium smegmatis is a bacterial strain related to the bacteria that causes the respiratory infection tuberculosis. This bacteria was the most sensitive to aromatic constituents in essential oils. Interestingly, this bacteria is the only one that has a mycomembrane comprised of phenolic glycolipids. This lipid-rich membrane allows the bacteria to be typically resistant to many drugs and has been related to its hyper-pathogenicity. The lipophilic nature of essential oils may be what allows these constituents to penetrate its lipid-rich membrane. Further investigation is warranted to explore the efficacy of essential oils against M. tuberculosis. With the rise of multi-drug resistant tuberculosis and extensive standard treatment protocols, investigation of other treatment options is imperative.
In general, finding alternatives to conventional antibiotics and novel bactericidal substances with a different mechanisms of action is vital due to the rise in antibiotic resistance. Essential oils provide a promising area of exploration to combat modern-day infections. The results suggested whatever gives MRSA the ability to be resistant to antibiotics does not give it the ability to be resistant to essential oils. This provides evidence that essential oils may be an alternative treatment option for MRSA infections. With continued research, essential oils could eventually be given in specific doses to treat infections like antibiotics including antibiotic resistant ones like MRSA.
The antimicrobial activity of the different essential oils are not the same, suggesting that different components and component concentrations are responsible for its range of activity. Previous research has shown that essential oils derived from whole plants are more powerful than the individual terpenes they are comprised of. Also, in research literature, certain combinations of terpenes provided increased level of antimicrobial activity. Unique and variable combinations of these constituents act together to achieve maximum efficacy. This supports naturopathic medicine’s philosophy of using the whole plant as medicine. Nevertheless, understanding how and what terpenes are contributing to its antimicrobial activity, will provide information to use them precisely, safely and efficaciously to treat infections.
Essential oils do in fact have antimicrobial activity in their airborne evaporative state. Rosemary, tea tree and cassia were found to fight a wide range of infections causing microorganisms. Other essential oils were found to have moderately broad antimicrobial activity including, from highest to lowest, thyme, cinnamon, oregano, white fir and frankincense. Rosemary, thyme and tea tree essential oils were found to be moderately effective against MRSA. Lemongrass, rosemary and thyme were found to be the best against one form of candida. Cinnamon, cassia, rosemary and thyme were effective against Bordetella bronchiseptica.
The anecdotal historical evidence of the antimicrobial activity of the aromatic constituents in essential oils is supported. This research lays the groundwork for further research projects to specifically identify active compounds and medical application. Simultaneously, the experimental design provides an innovative way to test essential oils in the laboratory that most closely relates to how they are used by consumers. Modern medical implications for this work may be related to the use of aromatic essential oils for respiratory or dermatological infections. Most importantly, there is promising application of this data to devastating infections like tuberculosis and MRSA. The results from this study are not conclusive and still needs further laboratory and clinical research. Currently, investigation into the specific terpenes and their mechanism of action are being explored to understand how to apply their broad therapeutic abilities.
Mareshah Abers, NMD is a resident at the Neil Riordan Center for Regenerative Medicine. Her goal is to find innovative solutions for pain, performance and quality of life in athletes and the everyday person. She emphasizes a whole-person approach to treatment and patient care. She is trained to listen and partner with her patients to help them get healthy and stay well. She graduated in the top of her medical school class at Southwest College of Naturopathic Medicine in the Regenerative Medicine Honors track. Dr. Abers focuses on treating pain and musculoskeletal conditions using physical and regenerative medicine techniques, products and devices. She offers perineural, prolotherapy and other orthobiologics like platelet rich plasma, bone marrow aspirate concentrate, and structural amnion/cord derived tissue. She has trained with many doctors in the valley to perfect her technique and develop her own approach. She continues to seek continuing education to provide the most up to date and cutting-edge treatment protocols. She utilizes many other treatment modalities to achieve patient’s goals including individualized botanical medicine, supplements, pharmaceuticals, nutrition and exercise which are tailored to each patient’s preferences and clinical presentation. Her philosophy is to address immediate pain concerns while providing a foundation for long-term results.