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Essential Oils & Science

Essential Oil Research and the Future

by Nicole Stevens, MSc

Mankind discovered long ago that plants are very beneficial when it comes to medicinal compounds, and so essential oils have been used in health and healing for centuries for many reasons, mainly, they work.

Since a stationary plant can’t exactly run to escape attacking predators and can’t fight them off with long claws or sharp teeth, they have evolved to protect themselves in other ways. Plants prepare some amazing concoctions of chemicals that serve as protection against microbes and pathogens. These chemical cocktails also help the plant regulate its internal processes of growth, development, reproduction, and metabolism.

So why can’t these chemicals provide the same benefits in the human body? Actually they can. Plants and people evolve in the same habitats. We all face pathogens, we all strive to grow and thrive in our development and we all face eventual aging.

Science is just the beginning to delve into the mechanisms by which essential oils and other natural products function. Although we don’t have all the answers yet, it’s becoming increasingly clear that there is great power and potential in essential oils. Researchers have found antibiotic, anti-viral, anti-fungal, anti-inflammatory and anti-cancer properties in various essential oils. They’ve found compounds that can aid in DNA repair, increase metabolism, improve blood flow, balance hormone levels, improve waste elimination, stabilize neurotransmitters, and relax muscles and lower stress.

A mammoth of information is being generated about how essential oils work. Hopefully, as scientists continue to study natural products and how they can best be used; our Western medicine models will embrace a more holistic approach to healing. We may find that drugs from a test tube aren’t the only way (or sometimes the best way) to treat our ailments.

A Fledgling Essential Oil Researcher

My own experience researching essential oil began when I was a graduate student at Brigham Young University. My original research project fell through, but luckily for me, my adviser had a box full of essential oils and an idea to screen them against various cancer cells, I was intrigued.

I think what first drew me into the project was the idea of doing some kind of life-saving cancer research. This terrible disease, in which a body’s own cells turn rogue and grow out of control, seems to be a scourge against which we have so few reliable cures. Like most people in this country, my life has been touched by cancer. My maternal grandfather has fought skin cancer for the past few decades and I lost a great-aunt to ovarian cancer. Being the naïve and starry-eyed college student, I wanted to join the noble fight against cancer.

But I was also fascinated by the essential oil.  At that point, I had no idea that these little amber bottles full of what I thought was basically perfume would prove to be so powerful.

I screened 70 essential oils against 5 different cancer cell lines. The procedure was fairly simple: I grew the cancer cells in Petri dishes until they were flourished, and then treated them with various concentrations of each oil. All tests were done in triplicate and repeated several times to make sure the results were consistent. Treatment Petri dishes containing essential oils were compared with untreated control dishes in which the cancer cells continued to grow as usual.

The results were astounding. Some essential oils were lethal against at least one cancer cell type, some oils killed multiple cancer cell types, and many of the oils were at least slightly inhibitory of cancer cell growth. But even more importantly—the essential oils showed little toxicity against non-cancer cells.

With these exciting preliminary results in hand, my taste for essential oil research grew insatiable. I wanted to test the oils against more cancer cells. I wanted to see just how powerful these oils were at increasingly low concentrations. I wanted to test them in living models to see if we could shrink tumors or stop lymphoma. I wanted to clone myself so I could do a thousand essential oil research projects simultaneously!

Let There Be Light

Life moves on and so did I. After graduation, before I could investigate more deeply into my original essential oil research project, my husband and I uprooted. I ended up at the University of Nevada, Las Vegas. But the move was a good one—I was able to get more involved in essential oil research with cancer cells. This time, there was a twist.

I learned of an emerging cancer treatment called photodynamic therapy (PDT). In this model, a patient is given a photosensitizing drug and then blasted with a specific wavelength of light. The idea is that the cancer cells, which are usually growing at a faster rate, will take up the photosensitizing drug more quickly than normal cells. Therefore, the light will kill cancer cells preferentially.

One of the biggest drawbacks of PDT is that the photosensitizing drugs can be highly toxic and cause damage to the kidneys, liver, and other body systems. Well, I thought, what if we used essential oil as a photosensitizing agent? Certain oils can increase photosensitivity when applied topically. Maybe we can cash in on that property to kill cancer cells but avoid toxicityof the traditional PDT drugs.

My preliminary results were very encouraging. Once again, I didn’t have time to explore as deeply as I’d hoped into my project. But I found that breast cancer cells could be treated with essential oils, exposed to short bursts of specific wavelengths of light, and we’d see dramatic death rates. Once again, this effect appeared to be focused on cancer cells rather than non-cancer cells.

Thank You, Ladies and Germs

Another move found me at the University of Utah. My boss was a remarkable researcher in her own right, and she was enthusiastic when I approached her about a new research project with essential oils. This time, I’d take a peek at the antimicrobial properties of some oils that have traditionally been used for cleansing and healing.

I worked late into the night, running tests on Salmonella and Klebsiella pneumonia and Escherichia coli and Staphylococcus aureus. My boss would joke with me that she could always tell when I’d set up an experiment – the lab smelled like an aromatherapy spa.

The results were impressive. Honestly, I’d come to expect astounding scientific performance from these essential oils! I found that at least one essential oil could wipe out even the nasty bugs like a staph infection and most of the microbes were susceptible to multiple essential oils.

Thyme, basil, oregano and cinnamon are powerhouses in the battle against microbes. Oregano is effective at killing a huge percentage of microbes even when it’s diluted to a concentration of only 1:5000.

The Work Must Go On

Every day there are more papers published about the amazing health benefits and disease-fighting properties of essential oils. This website will serve as a forum in which exciting essential oil research is presented and discussed, hopefully in ways that make the science more palatable and useful to everyone.

I hope to someday continue my own research with essential oils. Each of my projects has served to cement two facts in my mind. First, that high-quality essential oils are a powerful tool for promoting health and fighting disease. And second, that science has only begun to understand the potential of these plant chemicals.

Essential oils are slowly making their way into mainstream use. More doctors and practitioners are educating themselves about the benefits of holistic healthcare. The ranks of researchers who study essential oils and other natural products are making astounding discoveries. Ironically, the ancient secrets of traditional medicine are once again becoming the cutting edge of modern medicine.

It’s about time.

 Nicole Stevens is an essential oil enthusiast with a professional desire to increase the credibility and the scientific understanding behind natural products. She has been researching the various properties of essential oils for much of her career.

Nicole earned her undergraduate and Master’s degrees at Brigham Young University. Her Master’s Thesis was entitled “Bioassays to Determine Anti-Cancer Activity of Essential Oils.” For that project, nearly seventy essential oils and oil blends were tested against five different types of cancer in vitro.

In 2003, Nicole began working at the UNLV Cancer Research Center and completed a project looking at the possibility of using essential oils in a process called photodynamic therapy. This is a procedure that uses targeted photosensitizing chemicals and specific wavelengths of light to destroy cancer cells.

Essential Oils and gamma-aminobutyric acid (GABA) Neurotransmitter in Mental Health Disorders

Danielle Daniel
PsyD Candidate, California Southern University


Psychopharmacology defines the pharmaceutical drugs used to treat the psych or “mind” as it means in Greek.   Pharmaco, in the word psychopharmacology, also comes from the Greek word pharmakon, which means “poison” or “drug”.  New and developing research is showing evidenced based data of the psychoaromtic effects from the chemical constituents in essential oils.  Essential oils are the complex chemical structures found in the aromatic compounds in plants.  I have coined the term psychoaromacology to define this new emerging field.  Psych meaning “mind” in Greek, aroma coming from the Latin root of aromaticos, and logy also from Greek meaning the “science of, knowledge of, or study of”.  The field of psychoaromacology is a very promising science and holds a bright future for the treatment of mental health disorders.  Essentialology is the study of these aromatic compounds in essential oils.


Psychopharmacology and the modern medical model have a very specific treatment theory. The theory follows the concept of discovering what the body “normally” does and then implementing a synthetic pharmaceutical drug to be within “normality”.  The drug produces a chemical change in the body therefore requiring no lifestyle change by the individual.  A simple example of this is the use of psychopharmacological drugs involved with the activity of serotonin, the neurotransmitter commonly found low in many psychiatric disorders, including patients with bi-polar and other depressive disorders.  Selective serotonin reuptake inhibitors, SSRI’s, increase the serotonin activity in the brain by preventing the reuptake of serotonin from the synapses, therefore prolonging the effects of serotonin (Comer, 2010).   This appears to be a great solution to a wide spread and increasing problem in depression and other clinical disorders thought to be low in serotonin, however, an alternative viewpoint will consider not only augmenting a synthetic manner of receiving serotonin, but why the serotonin is low or not being absorbed or circulated in the first place? Also it is important to look at how can you naturally produce or receive more serotonin.  I would also pose another question offering an additional alternative view; is simply increasing serotonin the answer to treating these disorders?  In his book, The Second Brain, Dr. Michael Greshon, the Chairman of the department of Anatomy and Cell Biology at Colombia University, explains that 95% of our serotonin is found in our intestines (Greshon 1999).  This discovery proves the great connection that our brain chemistry and body have with one another and poses many alternative methods to simply treating disorders thought to be low in serotonin.  Dr. Emil Kraeplin posited that the etiology of all psychiatric disorders reside in the physical realm and originate in biological and genetic malfunction (Smith 2012).  So how can we naturally treat, produce, and restore brain chemistry?

In my research here, I have done a literature review on the chemical activity essential oils produce in the brain and in the body, therefore offering alternative methods of treatment for psychiatric disorders.   First I will go into a basis of biological effects of essential oils, then I will discuss specific research for treatment of psychiatric disorders using essential oils.

Essential Oils

Essential oils are concentrated natural chemical compounds found on plants.  Plant essential oils are hetergeneuous mixtures of lipophilic volatile hydrocarbon monoterpenoids and sesquiterpenoids.  They commonly consist in the hundreds of chemical constituents (Perry 2006) .   The oil acts as antibacterial, antiviral, antifungal, an insecticide and also protects the plant against herbivores  (Bakkali, Averbeck, Averbeck, & Idaomar, 2007). Whether the oils are inhaled or applied dermally, they enter the blood stream and produce measurable pharmacological effects.  Aromatically, the oil passes through the olfactory neural pathway which allows both intraneuronal and extraneuronal access to the brain.  Various research studies also have evidence that essential oils surpass the blood brain barrier influencing neurotransmitter activity (Perry 2006).  Being oil based, essential oils are able to penetrate the cells bi-lipid layer which then can destroy the replication of viruses without damaging the membranes, proteins or the DNA.  The cytoxicity of essential oils treat cells in the stationary phase of growth which make them highly antiseptic and antimicrobial (Bakkali, Averbeck, Averbeck, & Idaomar, 2007).  “The cytotoxic property is of great importance in the applications of essential oils…Essential oils or some of their constiuents are indeed effective against a large variety of organisms including bacteria, fungi, protozoa, parasites, acarids, larvae, worms, insects, and molluscus”  (Bakkali, Averbeck, Averbeck, & Idaomar, 2007 p.450).    Because essential oils can interfere with the mitochondrial functions, it adds pro-oxidant effects to the body and therefore becomes an antitumoral agent  (Bakkali, Averbeck, Averbeck, & Idaomar, 2007).

Certified Pure Therapeutic Grade

Before I elaborate further on the psychopharmacological effects of essential oils,  the grade and quality of oil must be mentioned.  Not every plant of the same species produces the same types or levels of chemical constiuents within it.  Also not every oil bottle you may find for purchase is free of harmful chemicals.  Therefore, in each research study, the chemical constituents of the oil are listed and it is highly recommend that before using oils for personal treatment, the quality and grade must be researched.  For a quality oil, a company will do various chemical analysis on every liter of oil to ensure it is free of toxins, pesticides, synthetics or any other unknown or harmful substance.  Second, via the chemcial analysis, a company will use the plants which contain the highest medicinal properties.  For example,  not every lemon tree produces the same amount of limonene, or not every thyme plant produces the same amount of thymol.   The only grade of oil that ensures this high quality is called Certified Pure Therapeutic Grade.

Neurotransmitter y-aminobutyric acid (GABA)


To illustrate the importance of ensuring the quality and the medicinal constituents within the oil, one study reports the effects of s-limonene on brain neurotransmitters, and found that when exposed to stress, s-limone inhibited the HPA activity which in turn caused an anti-stress effect via the y-aminobutyric acid (GABA) receptor (Zhou et. al. 2009).   GABA and its receptors are majorly distrubuted neurochemicals carrying inhibitor messages which cause a neuron to stop firing (Comer 2010).  GABA regulates GABAergic neurons including the activity of 5-HTergic nuerons in the dorsal raphe nucleus which projects throughout the hypothalamus, hippocampus, and amygdala.  This study orally administered s-limonene for 1 week to rats, and exposed them to stress via foot-shock, then studied the brain and found interesting results in the hypothalamus and amygdala regions.  The results showed that glutamic acid (Glu) decreased significantly while the concentration of GABA increased, which seems to have acted as an inhibitor to the bodies stress chemical responses.  The level of coricosterone, a stress hormone produced in the adrenal glands,  was significantly higher in the control group than that of the group administered s-limonene, showing that the s-limonene attenuated the release of corticosterone (Zhou et. al. 2009).

The involvement of the GABA system as a whole has been strongly linked to several neuropsychiatric phenotypes, especially anxiety.  The GABAa receptor is the site of action foranxiolytic drugs such as benzodiazepines and barbiturates.  One study on mice found that reduced GABAa receptors resulted in increased fear and reactivity toward natural stimuli (Xuam et. al 2009).  There are other neurotransmitters implicated in anxiety, however the theory, which continues to be supported by research involves a low concentration of GABA receptors or a malfunctioning of those receptors to capture the neurotransmitter data (Comer 2010).   In Schizophrenia, there are several neurotransmitter and brain systems affected also, including the GABAergic system.  Findings in the post-mortem tissue from patients with schizophrenia showed several changes in the GABAergic system (Damgaard et al 2011).  “Roberts (1972) proposed the involvement of deficits in the y-amino butyric acid (GABAergic) transmitter system in schizophrenia” (Damgaard et. al. 2011, pg. 402).  In one study, rats were treated with PCP, inducing a schizophrenic-like state of recognition and memory impairments, then they were administered a positive modulation of extra-synaptic GABA receptors.  The results showed a reversing effect of the schizophrenic-like state with the administration of the GABA receptors (Damgaard et. al. 2011).  There is significant evidence that GABA receptors are implicated in these disorders and the evidence shows that the essential oil constituent of s-limonene interacts therapeutically with the GABAergic system.  Limonene is found high in citrus oils, especially lemon oil, and could provide natural chemical results in the body with the inclusion in a daily routine.


Another oil having positive interactions with the GABAergic system is lavender.  I could not do a research paper on essential oils and mental health without mentioning lavender.  Lavender has amazing aromatic and therapeutic qualities. It is widely known for its sedative andanxiolytic effects.  There are many different species of lavender, however they do not all have the same phytochemistry and differ in the biological activities they produce.  Lavendula angustifolia Mill. from France, is highest in linalyl acetate and linalool which show the greatest results for anxiolytic and sedative properties. Research has shown that inhalation of the essential oil of l. angustifolia produces sedative effects similar to those of the pharmaceutical drug diazepam, or brand name Valium.  In one study, l.angustifolia blocked pentetrazol-, nicotine-, and electroshock-induced convulsions.  The data suggested that the main constituents in l. angustifolia, linalool and linalyl acetate, cause clinical sedative effects via the modulation of the components of the glutamatergic system.  The glutamatergic system is responsible for the excitatory neurotransmitter glutamate and serves as the precursor for the synthesis of the inhibitory GABA in GABAergic neurons (Perry & Perry 2006).  L. angustifolia and diazepam cause the same neurochemical effects as this study has shown, however, diazepam has many undesired side effects that lavender does not.  This offers a great solution again to excitatory states of anxiety disorders, schizophrenia disorders and even manic or hypo manic episodes.  Another study on lavender, orally administered l. angustifolia to participants exposed to anxiety provoking films and conducted several electro-dermal responses to measure the effects.  Those participants administered the lavender oil showed reduced anxiety responses via their heart rate, galvanic skin response, and heart rate variation measures in comparison to those of the control group who were administered a placebo (Bradley et. al. 2009).   Lemon and lavender from these studies both have anxiolytic like properties within their phytochemistry, and interact differently with neurotransmitters.  Both show promising results in reducing the body’s anxiety and stress responses and cause sedative effects.  There are no known toxicity or side effects from using either oil if infact they are “pure” as they are naturally produced by the earth.  There are many other essential oils that have been studied for their anxiolytic and sedative effects such as melissa, neroli, bergamot, roman-chamomile, marjoram, patchouli, rose, rosemary, and vetiver oil.  This offers many solutions for the myriad of disorders that have excitatory states, including that of ADD and ADHD.


One last area I have researched is of interest to discuss.  There is evidence that the inhalation of essential oils, increases neurogenesis in the adult mouse brain (Perry & Perry 2006).  Neurogenesis is the process of generating new neurons in the brain, which normally occurs during fetal development.  If new neurons are generated via essential oil inhalation, the brain has a greater possibility of healing from abnormal functioning.  Schizophrenia for example has the largest reports of structural and functional abnormalities in the brain causing a myriad of implications in behavior and functioning.  I have witnessed essential oils regenerating my skin tissue through the fading of 20 year old scars, and if they are powerful enough to regenerate the outer dermal layer, why not cerebral matter? If they are able to permeate the tiniest cell organelles within our cells to oxygenate and promote multi-cellular functions, why not inner brain cortices and functions? The answer is simple, they do.

Treatment of psychiatric disorders using essential oils is very promising and is free of adverse effects associated with conventional drugs.  Psychoaromacology is a safer option than pharmaceutical drugs and along with Dr. Kreplin’s and Dr. Greshon theories, the psychiatric and biological worlds are interconnected therefore to affect a change in the mental environment, taking one pill and not changing a dietary lifestyle is not the answer.  Nutrition and physical habits need to be examined and altered, and along with the use of essential oils, the human mind can have freedom from psychiatric imbalances.  Essential oils hold the most promising alternative solution for psychiatric treatment and will become the future as the preferred method.



American Psychiatric Association, 2000. DSM-IV-TR. American Psychiatric Publishing, Arlington VA

Bakkali, F., Averbeck S., Averbeck D., Idaomar M., (2007).  Biological Effects of Essential Oils – A Review. Food and Chemical Toxicology 46(2008) 446-475.

Ball, L. V. (2010). Odour-based context reinstatement effects with indirect measures of memory: The curious case of rosemary. British Journal Of Psychology, 101(4), 655-678.

Bradley, B. W. (2009). Effects of orally administered lavender essential oil on responses to anxiety-provoking film clips. Human Psychopharmacology: Clinical & Experimental, 24(4), 319-330

Comer, Ronald J. (2010). Abnormal Psychology (Seventh Edition) Worth Publishers New York

Damgaard, T. (2011). Extrasynaptic GABA receptor activation reverses recognition memory deficits in an animal model of schizophrenia. Psychopharmacology, 214(2), 403-413.

Eric Y.C. LaiCharng-Cherng ChyauJeng-Leun MauChien-Chou ChenYi-Jui LaiChing-Fang ShihLong-Liu, L. (2004). Antimicrobial Activity and Cytotoxicity of the Essential Oil of Curcuma zedoaria. American Journal Of Chinese Medicine, 32(2), 281-290.

Neuropsychopharmacology; new neuropsychopharmacology data have been

reported by investigators at federal university. (2012). Psychology & Psychiatry Journal, , 325. Retrieved from

Moss, M. (2008). MODULATION OF COGNITIVE PERFORMANCE AND MOOD BY AROMAS OF PEPPERMINT AND YLANG-YLANG. International Journal Of Neuroscience, 118(1), 59-77.

Perry, N., Perry E. (2006). Aromatherapy in the Management of Psychiatric Disorders: Clinical and Neuropharmacological Perspectives. CNS Drugs, 20(4), 257.

Reulbach, U., Bleich, S., Maihöfner, C., Kornhuber, J., & Sperling, W. (2007). Specific and unspecific auditory hallucinations in patients with schizophrenia. Neuropsychobiology, 55(2), 89-95. Retrieved from

Sanders, Laura (2011). Science News: A New Way to Breach the Blood-Brain Barrier.

Smith, T. (2012). Psychopharmacology: What you need to Know About Psychiatric Medications. CMI Education, Eau Claire, Wisconsin, U.S.A.

Xuan PhamCuie SunXiangning ChenVan den Oord, E. M. (2009). Association study between GABA receptor genes and anxiety spectrum disorders. Depression & Anxiety (1091-4269), 26(11), 998-1003.

Zhou, W., Yoshioka, M., Yokogoshi H., (2009).  Sub-Chronic Effects of s-Limonene on Brain Neurotransmitter Levels and Behavior of Rats. Nutritional Science Vitaminol, 55, 367-373.

 Danielle Daniels is currently pursuing her PhD at California Southern University. Her doctoral specialization is in psychoaromacology. She is a full-time licensed clinician in Californa (LCSW) and has over 20 years experience with using essential oils.  

Thyme oil can inhibit COX2 and suppress inflammation

Date: January 14, 2010

Source: American Society for Biochemistry and Molecular Biology

Summary: Researchers have found that six essential oils -- from thyme, clove, rose, eucalyptus, fennel and bergamot -- can suppress the inflammatory COX-2 enzyme, in a manner similar to resveratrol, the chemical linked with the health benefits of red wine. They also identified that the chemical carvacrol was primarily responsible for this suppressive activity.

Researchers have found that six essential oils -from thyme, clove, rose, eucalyptus, fennel and bergamot -- can suppress the inflammatory COX-2 enzyme, in a manner similar to resveratrol, the chemical linked with the health benefits of red wine.

For those who do not drink, researchers have found that six essential oils -from thyme, clove, rose, eucalyptus, fennel and bergamot -- can suppress the inflammatory COX-2 enzyme, in a manner similar to resveratrol, the chemical linked with the health benefits of red wine. They also identified that the chemical carvacrol was primarily responsible for this suppressive activity.

These findings, appearing in the January issue ofJournal of Lipid Research, provide more understanding of the health benefits of many botanical oils and provide a new avenue for anti-inflammatory drugs.

Essential oils from plants have long been a component of home remedies, and even today are used for their aromatherapy, analgesic (e.g. cough drops), or antibacterial properties. Of course, the exact way they work is not completely understood. However, Hiroyasu Inoue and colleagues in Japan believed that many essential oils might target COX-2 much like compounds in wine and tea.

So, they screened a wide range of commercially available oils and identified six (thyme, clove, rose, eucalyptus, fennel and bergamot) that reduced COX-2 expression in cells by at least 25%. Of these, thyme oil proved the most active, reducing COX-2 levels by almost 75%.

When Inoue and colleagues analyzed thyme oil, they found that the major component -carvacrol- was the primary active agent; in fact when they use pure carvacrol extracts in their tests COX-2 levels decreased by over 80%.

Story Source:

The above story is based on materials provided by American Society for Biochemistry and Molecular BiologyNote: Materials may be edited for content and length.

Journal Reference:

  1. Mariko Hotta, Rieko Nakata, Michiko Katsukawa, Kazuyuki Hori, Saori Takahashi, and Hiroyasu Inoue. Carvacrol, a component of thyme oil, activates PPAR-gamma and suppresses COX-2 expressionJournal of Lipid Research, January, 2010

American Society for Biochemistry and Molecular Biology. "Thyme oil can inhibit COX2 and suppress inflammation." ScienceDaily. ScienceDaily, 14 January 2010. <>.

Essential Oils May Kill Bacteria in the Cells Naturally

Can essential oils kill bacteria naturally? The problem of antibiotic resistance is growing - especially the problem of resistant bacteria in hospitals. Now a new study from Greece shows that some essential oils kill bacteria naturally - even bacteria that are resistant to antibiotics. This is encouraging news since using these oils could reduce the need for antibiotics - and help lower the number of antibiotic resistant bacteria that are causing so many problems for humans.


What are Essential Oils?

Essentials oils are oily liquids that are either distilled or pressed from the stems and leaves of plants. They've been used medicinally throughout history to treat various ailments and are now used in the practice of aromatherapy - as a form of alternative therapy to treat conditions ranging from anxiety to obesity. Their benefits come from the terpenes, phenols, aldehydes, ketones, alcohols, and other plant-derived chemicals they contain.


Essential Oils Kill Bacteria Naturally?

Greek researchers at the Technological Educational Institute in Greece, looked at the anti-bacterial potential of eight different plant-based essential oils. The big winners when it came to killing bacteria were thyme, Oregano and cinnamon essential oils. These oils were even effective against methicillin resistant Staph bacteria, also known as MRSA, which is responsible for so many drug resistant bacterial infections in hospitals. Of the two, thyme essential oil was most effective since it was able to destroy bacteria in under an hour. Other essential oils tested that effectively kill bacteria are peppermint and basil essential oils.


Why Aren't Essential Oils More Commonly Used to Kill Bacteria?

Research into the effects of using essential oils to kill bacteria is slow. Since they can't be patented, there aren't any drug companies to sponsor the research. Slowly, more studies are being done that confirm their ability to kill bacterial naturally. Other studies show that geranium, clove, lemon, lime, orange, rosemary oil, and, possibly eucalyptus oil also have antibacterial activity. Researchers are hoping that these essentials oils can eventually replace some of the synthetic preservatives that are currently added to foods - providing a safer, natural, and healthier alternative.


Anti-inflammatory effects of essential oils on human peripheral blood leukocytes.

The fungicidal and bactericidal actions of the essential oil (EO) of Melaleuca alternifolia seem well established, but their anti-inflammatory and antioxidative effects remain unclear. This study investigated in vitro the possible role of whole Melaleuca alternifolia EO as a modulator of the inflammatory/non-specific immune response by exploring the chemotaxis and kinetic radical oxygen species (ROS) production of leukocytes and cytokine secretion in peripheral blood mononuclear cells (PBMCs) in humans. The influence of Melaleuca alternifolia EO on the chemotaxis under agarose of isolated neutrophils (PMNs) was evaluated. The kinetics of ROS production by stimulated total circulating leukocytes was followed over 2 h by recording the fluorescence intensity of oxidized dihydrorhodamine 123. The effects of this EO on pro-(interleukin IL-2) and anti-(IL-4 and IL10) inflammatory cytokine secretions were determined by ELISA following incubation of PBMCs with the EO for 24 h. Melaleuca alternifolia EO was inefficient on the chemotaxis of PMNs. It exerted an antioxidant effect, reducing ROS production throughout the kinetic study. Melaleuca alternifolia EO inhibited PBMC proliferation, as revealed by a reduction in IL-2 secretion by stimulated lymphocytes. This EO at 0.1% directly increased the secretion of the anti-inflammatory cytokine IL-4 compared with IL-4 secretion without EO (18.5 +/- 10.0 vs 3.3 +/- 1, p < 0.05), and also increased IL-10 secretion at 0.01% (94.9 +/- 38.7 vs 44.1 +/- 18, ns). Melaleuca alternifolia EO may not only act as an anti-inflammatory mediator through its antioxidant activity but may also efficiently protect the organism by reducing the proliferation of inflammatory cells without affecting their capacity to secrete anti-inflammatory cytokines.

Copyright 2006 John Wiley & Sons, Ltd.


A Review on Anti-Inflammatory Activity of Phenylpropanoids

Found in Essential Oils



The search for alternative drugs capable of disrupting the inflammatory process  has become an important issue in scientific research, especially with reference to the use of natural substances and the reduction of undesirable side effects. Essential oils represent an important source of such substances, since their active constituents often exhibit an array of pharmacological properties, including anti-inflammatory activity. This review presents an overview of the anti-inflammatory action exerted by phenylpropanoids from essential oils and discusses possible mechanisms of action involved in the anti-inflammatory response, assessed through specific experimental models. Essential oils are natural volatile compounds that exhibit strong odors and are produced as secondary metabolites by aromatic plants [1]. They comprise complex mixtures of substances present

in quite different concentrations, such as terpene and phenylpropanoid constituents. Historically, they  have been used for various medicinal purposes, ranging from skin problems to cancer treatment and

are known for their antimicrobial, anti-inflammatory, sedative and analgesic properties [2]. Phenylpropanoids (Figure 1) are a large group of organic compounds produced by plants for  protection against infections, ultraviolet irradiation, wounding and herbivores. They are synthesized Molecules 2014, 19 1461 from the amino acid phenylalanine, that is converted into cinnamic acid. Reduction of the carboxylic acid group present in the cinnamic acid yields an aldehyde (e.g., cinnamaldehyde) and further reduction produces monolignols such as phenylpropenes (e.g., eugenol and safrole). Natural and synthetic phenylpropanoids are under current medicinal use for their pharmacological properties [3,4].  Figure 1. Phenylpropane skeleton. Inflammation is a biological response to noxious stimuli such as pathogens that cause tissue and cell damage [5]. It is considered a protective measure taken by the organism to remove harmful stimuli and to begin the healing process. It is classified as either acute or chronic, depending on whether it involves a short response or a prolonged one, respectively [6]. The acute inflammatory response is initiated by plasma and leukocytes infiltration to the site of injury or infection [7]. It can be triggered by receptors of the innate immune system, for example the toll-like receptors (TLRs) [8]. In the first steps of infection, resident macrophages and mast cells release inflammatory mediators, such as cytokines (e.g., interleukin-1β (IL-1β), IL-6, IL-12, and the chemokine IL-8), tumor necrosis factors  e.g., TNF-α and TNF-β), interferons (e.g., IFN-γ), eicosanoids (e.g., prostaglandins and leukotrienes) and vasoactive amines (e.g., histamine) [7]. These mediators exert complex regulatory roles in the inflammatory process in order to restore tissue homeostasis. Generally, cytokine production is induced by bacterial endotoxin or lipopolysaccharide (LPS) that activate TLRs (e.g., TRL-4) on the cell surface, initiating a series of intracellular events. The induction of innate immune and inflammatory responses by pathogens and non-microbial endogenous molecules

involves the participation of TRL4 that act via two major signaling pathways (i.e., MyD88- and  TIR-domain-containing adapter-inducing interferon-β (TRIF)-dependent pathway). TRL4 is a transmembrane receptor and a binding site for LPS. One of the first steps in the TRL4 signaling pathway triggered by LPS binding involves oligomerization of the receptor followed by interaction with the adaptor molecules MyD88 and TRIF [9], leading to activation of nuclear transcription factor kappa-B (NF-κB), a ubiquitous rapid response factor involved in immune and inflammatory reactions that triggers the release of IL-1, IL-6 and TNF-α [9]. In particular, IL-1 and TNF may stimulate additional inflammatory pathways resulting in eicosanoid and nitric oxide (NO) production, induction of all adhesion molecules, and further cytokine production [10,11]. Chronic inflammation, on the other hand, is a dysregulated response to persistent noxious stimuli  and seems to be related to tissue malfunction. This prolonged inflammatory condition is associated with a large number of chronic human disorders, including cancer, allergy, arthritis, atherosclerosis and autoimmune diseases [7]. In the past decades, the therapeutic potential of essential oils and their constituents has been the target of researchers in the pursuit of novel drugs of plant origin, particularly those exhibiting  anti-inflammatory action, to be used in the prevention or treatment of diseases [12]. With the intent to  provide information on this subject, this work presents a review of the anti-inflammatory effects of Molecules 2014, 19 1462  various phenylpropanoids that have been found to inhibit tissue inflammation in vivo and to modulate molecular pathways involved in inflammatory responses triggered by pro-inflammatory stimuli in vitro.



Considerable attention is being given to the discovery of novel drugs capable of fighting inflammation, particularly those of plant origin. Essential oils and their active constituents, such as the phenylpropanoids, are a promising source of anti-inflammatory substances and the data presented in this review show the potential roles the phenylpropanoids can display in this field. The information

available in the scientific literature indicates the participation of phenylpropanoids in different mechanisms of action related to the immunomodulation and suppressive action in the inflammatory response as disclosed in in vitro and in vivo experimental protocols. It is expected that further studies involving clinical trials will be carried out in order to ensure a safe use of these substances as a therapeutic agent against inflammatory diseases.

Synergistic effect between clove oil and its major compounds and antibiotics against oral bacteria

Moon SE, Kim HY, Cha JD
Archives of Oral Biology, 2011


Essential oils have been found to be antibacterial, antifungal, spasmolytic, and antiplasmodial activity and therapeutic effect in cancer treatment.

In this study, clove oil and its major compounds, eugenol and β-caryophyllene were evaluated against oral bacteria, either alone or in combination with ampicillin or gentamicin, via checkerboard and time kill assay.

The antibacterial activity of the clove oil was higher than β-caryophyllene but was similar to eugenol against all tested oral bacteria. Furthermore, the MIC and MBC were reduced to one half-one sixteenth as a result of the combination of clove oil or eugenol with antibiotics. Thesynergistic interaction was verified by time kill studies using the clove oil or eugenol with antibiotics. 60 min of treatment with MIC of the clove oil or eugenol with ampicillin or gentamicin resulted in an increase in the rate of killing in units of CFU/mL to a greater degree than was observed with alone.

The results suggest that the clove oil and eugenol could be employed as a natural antibacterial agent against cariogenic and periodontopathogenic bacteria.


Moon SE, Kim HY, Cha JD. Synergistic effect between clove oil and its major compounds and antibiotics against oral bacteria. Arch Oral Biol. 2011;56(9):907-916.

In vitro antibacterial activity of some plant essential oils

Prabuseenivasan S, Jayakumar M, Ignacimuthu S
BMC Complementary and Alternative Medicine, 2006


To evaluate the antibacterial activity of 21 plant essential oils against six bacterial species.

The selected essential oils were screened against four gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus vulgaris) and two gram-positive bacteria Bacillus subtilis and Staphylococcus aureus at four different concentrations (1:1, 1:5, 1:10 and 1:20) using disc diffusion method. The MIC of the active essential oils were tested using two fold agar dilution method at concentrations ranging from 0.2 to 25.6 mg/ml.

Out of 21 essential oils tested, 19 oils showed antibacterial activity against one or more strains. Cinnamon, clove, geranium, lemon, lime, orange and rosemary oils exhibited significant inhibitory effect. Cinnamon oil showed promising inhibitory activity even at low concentration, whereas aniseed, eucalyptus and camphor oils were least active against the tested bacteria. In general, B. subtilis was the most susceptible. On the other hand, K. pneumoniae exhibited low degree of sensitivity.

Majority of the oils showed antibacterial activity against the tested strains. However Cinnamon, clove and lime oils were found to be inhibiting both gram-positive and gram-negative bacteria. Cinnamon oil can be a good source of antibacterial agents.


Prabuseenivasan S, Jayakumar M, Ignacimuthu S. In vitro antibacterial activity of some plant essential oils. BMC Complement Altern Med. 2006;6:39(1-8).

New Studies Show Essential Oils Dissolve Biofilms to Eradicate Bacteria

Residence of Streptococcus bactaria within polymicrobial biofilm promotes antibiotic resistance and bacterial persistence in live cells.

Streptococcus pyogenes is a gram-positive bacterium that usually grows in pairs or chains. It has been classified as a beta-hemolytic streptococcus because when cultured on a blood agar plate all the red blood cells are ruptured by the bacteria (1). Furthermore, it has been classified using Lancefield serotyping as group A, because it displays antigen A on its cell wall. Therefore, this bacterium is commonly called the beta-hemolytic group A streptococcus, or GAS. (2) A picture of this clearly shows how the organism grows. Streptococcus pyogenes, also known as the flesh eating bacteria, is the most pathogenic bacterium in the whole genus (2). The name pyogenes comes from the word pyogenic, which is a classification for the streptococci that are associated with pus formation. The effects of this microbe range from mild illnesses such as strep throat infection and impetigo to more serious diseases such as P.A.N.D.A.S., scarlet fever, glomerulonephritis, and necrotizing fasciitis (3). However, if strep throat is untreated, it will lead to rheumatic fever, which is pretty rare now in the United States but was a more serious problem before the 20th century.

Part of the problem with all resistant bacterial infections is the formation of bio film  (a sticky shield) which the bacteria and fungi make to hide from our immune system thereby increasing antibiotic resistance.  In 2006, an article reported that another reason for the failure of antibiotics against Streptococcus pyogenes could be because of biofilm formation. Again, biofilm is a sticky gel like coating that the bacteria coats itself with to hide in. It will actually form colonies with other organisms to protect itself in this biofilm. To test this, 289 Streptococcus pyogenes strains were isolated and their abilities to form biofilms were analyzed. The experiment showed that most of the strains (90%) were able to form biofilms. The data also “indicated that biofilm-forming isolates entered epithelial cells with significantly lower efficiency than biofilm-negative strains.”  This suggests that if a certain strain could not enter epithelial cells to escape antibiotics, it would instead form biofilms as a means to survive in its host.  The conclusions of this research are very important because it shows that Streptococcus pyogeneshas alternative methods of surviving in its host. This study proved that antibiotics do not penetrate the biofilm, which is made of polysaccharides (long chain sugars), protein and minerals.  

Essential Oils Dissolve Biofilm

New studies show,  Essential Oils are very effective at dissolving biofilms and killing microbes. This microbial shelter can grow throughout the body, as this occurs, inflammation levels rise often leading to chronic and acute autoimmune disease states. Carvacrol and cinnamaldehyde (major constituents of oregano oil and cinnamon bark oil respectively) inhibits biofilm. Biofilm in Streptococcus, and Lyme’s disease infections is a more recent discovery. Melaleuca Essential Oils as well as the Citrus oils (found in Ningxia Red Juice) are very effective at breaking down biofilm, leaving the bacteria, viruses and or Lyme spirochetes more exposed to eradication.

New Studies Showing The Effectiveness Of Essential Oils Destroying Biofilm

  • Cinnamon bark: Staphylococcus epidermis biofilm (Nuryastuti et al 2009)
  • Oregano: S. aureus and S. epidermis biofilm (Nostro et al 2007)
  • Thyme: Listeria monocytogenes biofilm on stainless steel and polystyrene (Desai et al 2012)
  • Rosemary: Candida albicans and C. tropicalis biofilm (Chifiriuc et al 2012)
  • Tea tree: S. aureus, MRSA and C.albicans biofilm (Kwiecinski et al 2009, Park et al 2007, Sudjana et al 2012) 
  • Two essential oils eucalyptus and peppermint, showed 80.87%, 74.16%  biofilm reduction respectively. Minimum inhibitory concentration (MIC) values were calculated using agar dilution assay.Agarwal V, Lal P, Pruthi V.Molecular Microbiology Laboratory, Department of Biotechnology, Indian Institute of Technology, Roorkee, Uttarakhand 247667, India. vishudbs@iitr.ernet.inAbstract

Anti-biofilm, anti-hemolysis, and anti-virulence activities of black pepper, cananga, myrrh oils, and nerolidol against Staphylococcus aureus.

Anti-biofilm, anti-hemolysis, and anti-virulence activities of black pepper, cananga, myrrh oils, and nerolidol against Staphylococcus aureus.

Lee K1, Lee JH, Kim SI, Cho MH, Lee J.


The long-term usage of antibiotics has resulted in the evolution of multidrug-resistant bacteria. Unlike antibiotics, anti-virulence approaches target bacterial virulence without affecting cell viability, which may be less prone to develop drug resistance. Staphylococcus aureus is a major human pathogen that produces diverse virulence factors, such as α-toxin, which is hemolytic. Also, biofilm formation of S. aureus is one of the mechanisms of its drug resistance. In this study, anti-biofilm screening of 83 essential oils showed that black pepper, cananga, and myrrh oils and their common constituent cis-nerolidol at 0.01 % markedly inhibited S. aureus biofilm formation. Furthermore, the three essential oils and cis-nerolidol at below 0.005 % almost abolished the hemolytic activity of S. aureus. Transcriptional analyses showed that black pepper oil down-regulated the expressions of the α-toxin gene (hla), the nuclease genes, and the regulatory genes. In addition, black pepper, cananga, and myrrh oils and cis-nerolidol attenuated S. aureus virulence in the nematode Caenorhabditis elegans. This study is one of the most extensive on anti-virulence screening using diverse essential oils and provides comprehensive data on the subject. This finding implies other beneficial effects of essential oils and suggests that black pepper, cananga, and myrrh oils have potential use as anti-virulence strategies against persistent S. aureus infections.

In-vitro assessment of antioxidant and antimicrobial activities of methanol extracts and essential oil of Thymus hirtus sp. algeriensis.

In-vitro assessment of antioxidant and antimicrobial activities of methanol extracts and essential oil of Thymus hirtus sp. algeriensis.

Fatma G1, Mouna BF, Mondher M, Ahmed L.


Owing to the complexity of the antioxidant materials and their mechanism of actions, it is obvious that no single testing method is capable of providing a comprehensive picture of the antioxidant profile. The essential oil of the Thymus specie may still possess other important activities in traditional medicine, it can be used in the treatment of fever and cough. This essential oil may also have an anticancer activity.


The essential oils aerial parts hydrodistilled from Thymus hirtus sp. algeriensis, were characterised by GC/MS analysis and the methanolic extracts were chemically characterized by HPLC method. The essence of thyme was evaluated for its antioxidant and antibacterial activity.


The Terpinen-4-ol are the principal class of metabolites (33.34%) among which 1.8-cineole (19.96%) and camphor (19.20%) predominate. In this study, quantitative values of antioxidant activity of crude methanolic extracts of Thymus hirtus sp. algeriensis were investigated. The essential oils was screened for their antibacterial activity against six common pathogenic microorganisms (Escherichia coli, Pseudomonas aeruginosa, Salmonella enteridis, Staphylococcus aureus, Bacillus subtilis and Listeria monocytogenes) by well diffusion method and agar dilution method (MIC). All the essences were found to inhibit the growth of both gram (+) and gram (-) bacteria organisms tested. These activities were correlated with the presence of phenolic compounds in active fractions. HPLC confirmed presence of phenolic compounds in methanol extracts.


Methanol extracts and essential oils from aerial parts of Thymus hirtus sp. algeriensis, were examined for their potential as antioxidants. The technique for measuring antioxidant activity, which was developed using DPPH, ABTS and β-carotene bleaching, produced results as found in established literatures. The present results indicate clearly that methanol extracts and essential oils from Thymus hirtus sp. algeriensis possess antioxidant properties and could serve as free radical inhibitors or scavengers, acting possibly as primary antioxidants, also their essential oil have an antibacterial effect.

In Vitro Antibacterial Activity of Essential Oils against Streptococcus pyogenes.

In Vitro Antibacterial Activity of Essential Oils against Streptococcus pyogenes.


Streptococcus pyogenes plays an important role in the pathogenesis of tonsillitis. The present study was conducted to evaluate the in vitro antibacterial activities of 18 essential oils chemotypes from aromatic medicinal plants against S. pyogenes. Antibacterial activity of essential oils was investigated using disc diffusion method. Minimum Inhibitory Concentration of essential oils showing an important antibacterial activity was measured using broth dilution method. Out of 18 essential oils tested, 14 showed antibacterial activity against S. pyogenes. Among them Cinnamomum verum, Cymbopogon citratus, Thymus vulgaris CT thymol, Origanum compactum, and Satureja montana essential oils exhibited significant antibacterial activity. The in vitro results reported here suggest that, for patients suffering from bacterial throat infections, if aromatherapy is used, these essential oils, considered as potential antimicrobial agents, should be preferred.

In Vitro Antibacterial Activity of Essential Oils against Streptococcus pyogenes.


Streptococcus pyogenes plays an important role in the pathogenesis of tonsillitis. The present study was conducted to evaluate the in vitro antibacterial activities of 18 essential oils chemotypes from aromatic medicinal plants against S. pyogenes. Antibacterial activity of essential oils was investigated using disc diffusion method. Minimum Inhibitory Concentration of essential oils showing an important antibacterial activity was measured using broth dilution method. Out of 18 essential oils tested, 14 showed antibacterial activity against S. pyogenes. Among them Cinnamomum verum, Cymbopogon citratus, Thymus vulgaris CT thymol, Origanum compactum, and Satureja montana essential oils exhibited significant antibacterial activity. The in vitro results reported here suggest that, for patients suffering from bacterial throat infections, if aromatherapy is used, these essential oils, considered as potential antimicrobial agents, should be preferred.

Lavender Essential Oil For Anxiety

Essential oils and gut bacteria

Effects of Essential oils on Bacteria in the Gut

Gastroenterology Research and Practice
Volume 2012 (2012), Article ID 457150, 6 pages

Review Article

Development of Probiotic Candidate in Combination with Essential Oils from Medicinal Plant and Their Effect on Enteric Pathogens: A Review

Shipradeep,1 Sourish Karmakar,1 Rashmi Sahay Khare,2 Sumedha Ojha,1 Kanika Kundu,2 and Subir Kundu1

1School of Biochemical Engineering, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, India
2Chemistry Section, MMV, Banaras Hindu University, Varanasi 221005, India

Received 17 March 2012; Revised 4 May 2012; Accepted 12 May 2012

Academic Editor: Antonio Gasbarrini

Copyright © 2012 Sourish Shipradeep et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Medicinal plants and probiotics both have very high potential in terms of their antimicrobial activity against antibiotic-resistant enteric pathogens. The probiotics being enteric microorganism do not have any parasitic effect on human beings. They have been an integral part of daily food for centuries. They have been shown to have health beneficiary properties. The probiotics retard the growth of the microorganisms, while essential oil kills them. Combining the effect of medicinal plant extract and probiotics may be a new approach due to their complementary antimicrobial effects and practically no side effects. The synergistic effect of the essential oil and probiotics will be necessarily higher than using them alone as health product.

1. Introduction

The plants have been used in Ayurvedic medicines from ancient times. The extracts from these plants have shown potent antimicrobial effect. Recently, much work has been done on extraction of chemicals responsible for the antimicrobial effect from these plant species. It has been reported that the essential oils extracted from these plants have potent activity against microorganisms [1]. However, the studies have shown that these essential oils have very high MIC (minimal inhibitory concentration) against beneficial enteric bacteria known as probiotics [23].

Probiotic is the term as per WHO definition denotes “live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance.” As the definition clearly indicates, most of the intestinal bacteria have an important role to play in the digestive system. Earlier, probiotics were given to animals to improve their health, but later much research has been put in the development of the probiotics for human health. The major probiotics that are taken in the diets belongs to the genera ofLactobacilli and Bifidobacteria [4]. Apart from that, the gut flora predominately has obligate anaerobes that include Bifidobacteria, Clostridia, Eubacteria, Fusobacteria, Peptococci, Peptostreptococci, andBacteroides. Only about 1% of these bacteria are facultative anaerobes belonging to the genera ofLactobacilli, Escherichia coli, Klebsiella, Streptococcus, Staphylococcus, and Bacilli. In the case of newborns, food habits play a major role in the development of enteric flora. The breastfed babies normally have abundance of Bifidobacteria, while the others have complex microflora in their enteric system.Bifidobacterium sp. can be isolated mostly from the feces of infant milk feed baby. However, in the case of infants fed on normal formula based food products the gut flora is found to be rich in Enterobacteria, Lactobacilli, Bacteroides, Clostridia, and Streptococci. These gut flora help to digest the milk-based food and offer the primary line of defense against the pathogenic bacteria. The infants have weak but developing immune system [5]. These enteric bacteria help the infantile immune system to fight against pathogenic enteric bacteria by lowering the pH of the gut, rendering it unsuitable for pathogenic bacteria to survive [6]. Even the medical practitioners recommend probiotics-based supplement to both patients suffering from enteric diseases. The most popular probiotics supplements belong to the genera of Lactobacilli andBifidobacteria. The recommended dosage of 109–1010 CFU is considered a minimum for healthy enteric system [7].

Present review emphasizes on the synergistic antimicrobial effect of essential oil of the Lamiaceae family and probiotics administered together as flavored fermented milk products. The advantage of using such a combination is its beneficial effect with its antimicrobial property. The probiotics can help in improving the gut epithelial conditions while essential oil acts on killing the pathogens present in the human body.

2. Health Benefits of Probiotics

Probiotics, though recently popular, have been an integral part of the human diet for centuries. All the civilizations from ancient times have documented the benefits of curd in the human diet. The lactose-tolerant people are always advised to take curd with their diet. The curd is rich in Lactobacillus sp. andStreptococcus sp. These microorganisms utilize the lactose present in milk-based food and convert it to lactic acid [8]. The occurrence of flatulence in carbohydrate-intolerant individuals is also observed with fatty acid. The carbohydrates that are not fully digested due to lack of certain enzymes in human being can also be digested with probiotics. These carbohydrates are fermented into short-chain acids such as butyric acid, lactic acid, or acetic acid [9]. These acids are readily utilized in by human cells for ATP metabolism providing energy to the individuals. The lactic acid also helps in protein metabolism by coagulating the protein chunks from meat inside the intestine [10]. Formation of hydrogen peroxide is also prevented by catalases produced from probiotics preventing protein-caused rancidity [1113]. Hydrolysis of sarcoplasmic protein was also observed with many species of Lactobacillus genus [1416]. Coprecipitation of cholesterol with bile salts at lactic acid-induced lower pH is also observed in in vitro conditions [17].

Probiotic microorganisms are also found to be involved in synthesis of vitamins. The probiotics microorganisms are known to synthesize biotin and vitamin K [18]. Apart from that, they are also involved in the ions absorption such as Mg2+, Ca2+, and Fe3+.

The probiotic microorganisms are also involved in the enhancement of expression of certain pattern recognition receptors. Pattern recognition receptors such as TLRs have active role in wound healing process. The intestinal cells have high need for these receptors for supporting their process of proliferation and differentiation, healing the wounds made due to irregular bowel movement [19]. The short-chain fatty acid produced from carbohydrate metabolism also enhances the process of proliferation and differentiation of gut epithelial cells.

The probiotics have also a major role to play in prevention of allergies in children [5]. However, the connection of probiotics and immune system regulation is still under investigation. It has been observed that with allergy-prone adults and children, the count of Lactobacilli and Bifidobacteria is lower. It has been also observed that administration of probiotic strains during prenatal stage can decrease the chance of atopic eczema. In addition, the production of pattern recognition receptors, interleukin, and growth factors from the probiotic microorganisms in gut epithelia also play an important role in prevention of allergies. Therefore, it can be inferred that these microorganisms have direct role in immune system regulation [5]. Apart from that, these microorganisms also play a role in immune response modulation. The probiotic microorganisms interact with the gut-associated lymphoid tissue (GALT) [20]. The probiotics are involved in cytokine synthesis, that plays an important role in immune system regulation. However, due to insufficient clinical trial, administration of probiotics in immunosuppressed individuals is still prohibited.

It has been also observed from both in vitro and in vivo studies that probiotics may prevent cancer [21]. It has been found that daily intake of fermented milk products substantially decrease the concentration of nitroreductases, azoreductases, and β-glucuronidase in the gut. These microbial enzymes are associated with carcinogen production in the gut [22]. Lactobacillus casei have also shown an antigenotoxic effect. It prevents inducible DNA damage in the tumor target tissues of gastrointestinal tract of rats.

3. Antimicrobial Effect and Mechanism of Action

Probiotics have a known antimicrobial effect. They are very potent against pathogens. There are several proposed mechanisms for the antimicrobial action of the probiotics. Bacteriocins, organic acids, hydrogen peroxide, diacetyl, and other inhibitory chemicals are released by the probiotics [23]. All of these chemicals are known for their potent antimicrobial effects. Bacteriocins are toxic chemicals released by the probiotics, that are highly potent against most of the bacteria. However, the most feasible mode of action seems to be lowering of pH with release of organic acids such as lactic acid [2425]. In the limiting condition of available substrates inside the intestine, lowering the pH ensures the survival of acidophilic micro-organisms only. The growth of the pathogens gets inhibited at acidic conditions, slowing the metabolic process in them. Lactobacillus strain GG has been reported to produce inhibitory chemicals, possibly a microcin, that have high activity against pathogenic microorganisms. It has been found effective against Clostridium spp., Bacteriodes spp., Enterobacteriaceae spp., Staphylococcus spp., and Pseudomonas spp. in microbiological assays. Lactocidin released by strains of lactobacillus acidophilus is found active against Staphylococcus aureus and Pseudomonas aeruginosa [26]. There has been a study thatLactobacillus acidophilus LB release chemicals that are effective against both gram positive and gram negative microorganisms. These chemicals released in the broth were effective against Staphylococcus aureus, Listeria spp., Salmonella typhimurium, Shigella flexneri, E. coli, Klebsiella pneumoniae, Bacillus cereus, Pseudomonas aeruginosa, and Enterobacter spp. [27]. However, the chemical did not have any inhibitory effect on probiotics strains such as Lactobacillus and Bifidobacterium spp. This can be explained by the similarity of survival conditions of both these microorganisms. Some of the strains ofBifidobacterium spp. have potent activity against Salmonella typhimurium. However, not all the strains ofBifidobacterium spp. have the activity against S. typhimurium. All of the probiotics have higher survivability in low pH conditions. These microorganisms produce acids by breaking the carbohydrate present in the diet. The properties of acid production and acid survivability increase their survivability in the toughest of conditions [2829]. The adherence property of the probiotic microorganisms also ensures their longevity in the human guts [30]. However, the probiotic strains have shown an effective potential in inhibiting the adhesion of pathogen such as E. coli and Salmonella enterica in in vitro conditions [31]. The potential of adhesion inhibition by the probiotics is credited to the mucin production and competitive binding to gut epithelial receptor sites. Lactobacillus acidophilus LA1 has high calcium independent adhesive property that inhibits the invasion of enteropathogenic bacteria. Mucins are complex glycoprotein that inhibits the enterobacterial adhesion by protection of intestinal epithelial cell receptors. Both MUC2 and MUC3 produced by Lactobacillus spp. are potent examples of Mucins that have adhesion inhibitory activity against enteropathogens.

4. Antimicrobial Effects of Essential Oils from Medicinal Plants

There has been lot of studies in recent year that have established the antimicrobial effect of essential oils of medicinal plants such as plants of the Lamiaceae family [23]. The essential oils predominately present in the leaves of the plant species have a pleasant aroma. They are commonly used in flavor enhancement in food industries, as they are safe for human consumption. These essential oils have been shown to have a bactericidal effect. The plant species of Lamiaceae family have been proven effective against Uropathogen [32]. Table 1 shows the MICs of Coleus aromaticus and Ocimum sanctum (Rama Tulasi andShayama Tulasi) against few known enteric pathogens [32]. The essential oil from the plants of Carum carvi, Coleus aromaticus, Rama Tulasi, Shyama Tulasi, Citrus aurantium var. amara, foeniculumvulgare dulce, Illicium verum, Lavandula angustifolia, Mentha arvensis, Mentha x piperita, and Trachyspermum copticum have been shown to be effective against variety of microorganisms. These plants extracts have been found effective against Bacteroides fragilis, Candida albicans, Clostridium difficile, Clostridium perfringens, Enterococcus faecalis, Escherichia coli, Eubacterium limos, Staphylococcus aureus, Klebsiella oxytoca, Proteus vulgaris, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, and Peptostreptococcus anaerobius [2]. The MICs against these microorganisms varies from 0.1 to 3%v/v. The MICs of the same plant extracts against probiotic microorganisms such as Bifidobacterium bifidum, Bifidobacterium longum, Lactobacillus acidophilus, and Lactobacillus plantarum are much higher in magnitude than the pathogens [2]. Therefore, if the dosage of essential oil is low, then it effectively wipes out the pathogens without harming the beneficial probiotics.

Table 1: MICs of essential oil against known pathogenic microorganisms.

5. Proposal on Synergistic Effect of Probiotics and Essential Oil from Plants

The essential oils have high MIC values for probiotics, while it is effective in much lesser concentration against the pathogens. The above phenomenon makes it possible that both probiotics and essential oil can be administered together to cure pathogenic infection in human gut. They both can be combined to form essential oil-flavored fermented milk products such as flavored curd beverages or flavored yogurt. Antibiotics coupled with probiotics are already present in the market, but these medicines mostly face stiff challenge from antibiotic-resistant bacteria. Further frequent use of the antibiotics may lead to the development of antibiotic resistance in the pathogenic microorganisms too. Hence, the strategic use of probiotics may be beneficial to curb the growing phenomenon of antibiotic resistance. Probiotics have antimicrobial properties associated with the production of bacteriocin-like chemicals. However, it mostly arrests the proliferation of the pathogens by lowering the pH in the gut environment. The pathogens do not normally have any mechanism against the action of essential oils. Essential oils are resistant against enzymatic activity of β-lactamase produced as a countermeasure against β-lactam antibiotics. The use of probiotics lowers the survivability chances of pathogen, while the essential oil in lower dosage ensures their complete killing inside the human digestive tract. The probiotics may also impart its good benefits discussed earlier. Apart from that, the fermented milk product will surely impart benefits in terms of supplying nutrients such as sugar, water, salt, and acid to the human body. Adding essential oil will not only give an aromatic flavor to these fermented milk beverages or products, but also increase their shelf like considerably by preventing the microbial spoilage. The product will act as both probiotic health product and preventive antimicrobial product against enteric pathogens.

In an independent study, beverages A, B, and C were prepared with probiotic curd (109 CFU/ml) [33] with varying concentration of essential oil of Coleus aromaticus, Rama Tulasi and Shyama Tulasi, respectively [1]. The beverages A1, A2, and A3 were prepared with essential oil of Coleus aromaticus; beverage B1, B2, and B3 with essential oil of Shyama Tulasi and beverages C1, C2, and C3 with essential of Rama Tulasi in varying concentrations of 1, 2, and 3 μl/ml respectively. These beverages were then grown with common enteric pathogens in equal concentration, measured by count of CFU, in nutrient broth for 24 hours in airtight culture vials at 37°C to simulate the anaerobic condition prevailing in the intestine [34]. The individual vial was tested for the traces of pathogen as seen in Table 2 with − sign indicating the cidal effect of the beverage against the pathogen (no growth of the pathogens), while + sign indicated the growth of the pathogen. The sample beverages were found to be highly effective in inhibiting the growth of the pathogen. The shelf life of the beverages was also found to be significantly higher than normal probiotics [34]. The test results can be interpreted as the beverage’s capacity for prevention against enteric pathogens. The use of beverage does not need the stringent FDA regulations, yet it will impart the benefit of preventive diseases.

Table 2: Test of the beverages made with mixing different concentration of essential oil of Coleus aromaticus, Rama tulasi, and Shyama tulasi against common pathogens for 24 hrs at 37°C (− sign denotes no pathogen; + sign denotes the presence of pathogen).

6. Conclusion

Probiotics and essential oils both have a great potential in terms of their beneficial effect against microbial gut infection. They also show a synergistic effect that is normally higher than any known drug due to their complementary actions. Since most of these medicinal plants are edible, their extracts as food product do not have any side effects with low dosage. Therefore, these products may be very beneficial for human beings. However, much research is needed to be put into these studies, as drug regulatory authorities still have strong regulations against usage of plant extracts as medicines.


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