Antimicrobial effects of tea tree
A literature review by Aoife O’Toole
Herbal science 4
Tea tree oil, microbes, Propionibacterium acnes, skin,
methicillin resistant Staphylococcus
aureus, antimicrobial, constituents
Regardless of growth in present knowledge,
the healthcare industry is continually fraught with the dread of microbial
infections. Misusing antibiotics has furthermore intensified this, creating a growth
of antibiotic-resistant pathogens. Attempts to acquire novel procedures for regulating
bacterial infections are very vital. Therefore , essential oils such as tea
tree oil have arose as new, feasible, and harmless selections for the handling,
or abolition of these microbes. Tea tree oil constituents are talked about in terms
of current usages and future competence as antimicrobials. They have existed for
thousands of years and previous to any contemporary drugs which are now around.
This review tries to propose an explanation of by what means tea tree essential
oil can be used and how they should be used in the future to prevent and treat bacterial
Tea tree oil is a predominant essential oil used
characteristically for its strong antimicrobial properties. It is easily
evaporated at normal temperatures, and it is obtained from an Australian plant called
Melaleuca alternifolia. It is extensively
used to handle a number of conditions. Tea
tree oil (TTO) is characteristically connected with skin complaints such as
acne, which is caused by a microbe recognized as Propionibacterium acnes. Antibiotics are typically recommended to handle
this condition though there are currently antibiotic resistant strains existing(Coates
et al. 2002).
Brief history. Tea Tree Oil first became known to the western world in around
1732. It was discovered by Captain James Cook when he reached Australia. He discovered
a warm and invigorating tea from the leaves of the Melaleuca Alternifolia tree. It was from this that the plant became
known as “tea tree”. The indigenous Australians at that time used it to cure skin
diseases and wounds. When he comprehended this he went back with a sample of
the herb and had a medic inspect it for its curative possessions. The doctor
confirmed that it had an influential antiseptic trait. Shortly hereafter, the
use of TTO expanded, and it is now well-known worldwide as a non-synthetic antimicrobial
(Halcon et al. 2003).Australia is the only country where Melaleuca Alternifolia breeds so it must be transferred to various countries.
Chemical components. Tea tree oil is made up of many different chemical
elements that give it its antibacterial powers. The four main biochemical
components of tea tree oil would be as follows; Terpinen-4-ol, ?-Terpinene, ?-Terpinene
and Terpinolene (see table 1).
Table 1. Approximate
percentages present of various biochemical components of TTO
Quantity existing (approx.)
The other 40 % includes many different components which
are existent in smaller amounts. Some additional components are; ?-Terpineol, ?-Pinene,
Limonene and ?-Cymene. There are about 98 components which can be present in
tea tree essential oil. The strengths of these constituents can vary for every
separate oil. However, there stands to be clear criteria put in position by the
Australian and International Standards Organizations to ensure value of the oil
i.e. a lowest and highest potency range for each constituent (Halcon et
al.2003). Tea tree oil can come in six different biochemical combinations. There
is a terpinen-4-ol kind which is produced on an industrial scale, a terpinolene
type, and four 1, 8-cineole types.
As was specified earlier, people internationally are conscious
of the antimicrobial properties of tea tree oil. In current times alternative remedies
are becoming extra popular. This review accumulates present growths in the acknowledgement
of the antimicrobial ability of TTO and its components, as well as scientific efficacy.
Precise ways of antimicrobial action are revised and analysed, mostly with
regards to skin bacteria to see if it would be possible to substitute it
instead of traditional treatments such as antibiotics and severe chemicals.
TTO shows antimicrobial action against a great range of
Gram-positive and Gram-negative bacteria, yeasts and fungi (Kulik et al.2000). However
it usually is more active to
Gram-positive than to Gram-negative microorganisms. The microorganisms that
will be concentrated on in this review are two gram positive microbes that target
the skin, Propionibacterium acnes and
methicillin resistant Staphylococcus aureus (MRSA) .We will likewise observe the fungus athlete’s foot.
Propionibacterium acnes. Tea-tree oil is a popular constituent of skin
preparations, and a number of its suggested usages indicate an anti-microbial
effect (Drury 1991). Tea-tree oil is recommended for the treatment of acne
vulgaris. A report associating a tea-tree oil gel to benzoyl peroxide lotion
demonstrated the efficiency of the oil intended to treat the disorder (Bassett
et al. 1990). Propionibacterium acnes
and coagulase-negative staphylococci have been implicated in the pathogenesis of
acne vulgaris (Shanson 1989), and it is possible that the oil works by
eradicating these microorganisms from acne lesions. Propionibacterium acnes (P.acnes)
settle on the skin and hair follicles. They are oxygen-tolerant, anaerobic
bacteria that favour low oxygen surroundings. They can develop sticky lumps
known as biofilms that help them to attach to surfaces and regulate their
environment (http://thescienceofacne.com/what-is-propionibacterium-acnes/). In
many situations, bacterial biofilms have been proven to add to long term
infections, and could help with the perseverance of P. acnes infection in some individuals. Because they are gram
positive microbes they have bulky cell walls that aid with defending them from
their surroundings. Still these thick cell walls let hydrophobic particles pierce
the cells without any difficulty and move through the cell wall and inside to the
cytoplasm. Phenolic compounds work this way and they are present in TTO, showing
antimicrobial action against Gram-positive bacteria such as P.acnes (Nazzaro et al. 2013). There are
plenty of other gram-positive bacteria that create infections, such as MRSA.
Methicillin resistant Staphylococcus aureus (MRSA). MRSA is a major cause of hospital
infections and is becoming increasingly difficult to battle as is it becoming resilient
to all present classes of antibiotics. About 30% of burn lacerations become
colonized by MRSA in medical centres. Other possible treatments are being
sought after and are hopefully forthcoming for the treatment of MRSA; essential
oils are of specific interest. TTO is proven to be effective in treating this
antibiotic resistant strain of Staphylococcus;
although there are worries over its toxic capacity. Even though essential oils
are popular for being antimicrobial, they are still less likely to be used by
medical experts. This is solely due to lack of scientific evidence. Additionally
common medical care is extremely extensively accessible. Edwards-Jones et al. 2004
conducted a report trying to prove the efficacy of essential oils as antimicrobial
agents. The five oils used in the experiment carried out were tea tree,
lavender, geranium, patchouli and citricidal. TTO had the maximum clearing zone
when put in direct contact with two different strains of Staphylococcus aureus.
Essential oils undoubtedly work, so there is no reason
they shouldn’t be used to treat these bacteria. There is great potential for the
use of essential oils as natural antibiotics to control infections, especially contagions
of the skin. They could also be used to minimise antibiotic resistant strains
of microorganisms. If there is no new research done into discovering more antibiotics,
by the year 2050 a person will decease every three seconds from a microbial
illness (WHO). Since no novel antibiotics are being exposed it is long overdue that
we seek out natural substitutes. It is also important for money to be put into
researching essential oils in more detail. As well as being antibacterial, TTO
is also familiar with being antifungal.
Athlete’s foot. TTO is popular as being effective in
controlling the fungi that cause athletes foot. The fungus is known as Tinea pedis. It is often found in
people whose feet have become really humid from sweat while being covered in
tight shoes. It is transferable and can be dispersed through affected floors,
towels or clothing. In a 1972 study done on various foot problems, Dr. Walker
used tea tree oil in three different formulas to try combating these problems. To
start was unmixed oil, secondly was a mixture of 40% oil with 10% isopropyl
alcohol. This was known as Melasol. Third was 8% oil with lanolin and
chlorophyll and this was in ointment form. 60 people took part in the
experiment. 40 took Melasol, 20 used the ointment and 8 applied the unmixed oil.
The medical care changed from three weeks to four years. Of 68 patients, 58 got
alleviation from their foot ailments over a time frame of 6 years. There are
four if not more various fungal diseases associated with athlete’s foot and
each of these display sensitivity to TTO.
Conventional treatments for fungal disease of the nails include;
debridement which is removing alien materials and impaired tissue from the nail,
and also there are topical treatments. This review evaluated the effectiveness of
topical treatments of 1% clotrimazole solution in comparison with 100% TTO for treating
of Tinea unguium which is a fungal
infection of the toenail. In a 6 month
double-blind, multicentre, randomised, controlled trial of 117 people with
a Tinea unguium
infection, patients got twice-daily
treatments of either 1% clotrimazole (CL) solution, which is topical antifungal
drug medication, or 100% (TTO). The fact the trial was double blind meant that
neither party were aware of what the therapy that they were getting was. This aided
with removing bias. The fact it remained a randomised trial ensured there was
no selection prejudices from the people who carried out the trial.
Debridement and medical evaluation were carried out at 0,
1, 3 and 6 months. Samples were taken at 0 and 6 months. After 6 months, the both
groups were associated based on culture cure (CL=11%, TTO=18%). Three months on,
almost half of both factions stated that they had persistent positive
development. The conclusion was, even though all ongoing treatments have high reoccurring
percentages, using a topical application along with debridement is a good
treatment to start with. Topical treatment, with regards to the previous two
concoctions, provides benefit in how the nail looks and any symptoms associated
with it, whereas oral treatment has the limitation of price and likely bad
repercussions. This experiment reinforced the necessity to use a strong (in
this case 100%) concentration of TTO to achieve improved short-term and
long-term efficiency. In children and people with sensitive skin, a 70%
solution may be superior.
There are a few ways TTO could be tested in vitro. These
include dilution, disk diffusion and agar well diffusion. We will now look at
different ways the antimicrobial properties of TTO have been tested and the
data that has been delivered from these tests.
Dilution. A report carried out by Walton et
al in 2004 attempted to demonstrate the in vitro sensitivity of Sarcoptes scabiei var hominis to
Terpinen-4-ol. The parts of TTO known as; terpinen-4-ol, terpineol, and
1,8-cineole were utilized in vitro at concentrations equal to those in 5% TTO.Terpinen-4-ol
makes up 42% of TTO and was utilized at a concentration of 2.1%, TTO consists
of approximately 3% terpineol and was used at a concentration of 0.15%, and
1,8- cineole makes up 2% of TTO and was utilized at a concentration of 0.1%. Also,
mites were exposed to all 3 parts of TTO in a combined mix and to 5% TTO directly.
An ivermectin solution of 100 µg/g was also used for comparison along with Emulsifying
Ointment. The 5% TTO
and active component terpinen-4-ol were efficient in reducing mite presence. Differences
were observed in the mites survival graphs for 5% TTO, terpinen-4-ol, and
ivermectin when compared to the control which was Emulsifying Ointment. Change was
seen in survival rates among every part of TTO. 85% of the mites had deceased
after 1 hour when shown to 2.1% terpinen-4-ol. Contrary to this, almost 40% and
60% of mites had not deceased after 16 hours of exposure to 0.15% terpineol and
0.1% 1,8-cineole. It was interesting to see that 60% of mites had deceased after
1 hour of exposure to 5% TTO. There is currently no vaccine for scabies and the
growth of future medicines is lacking. The rise of drug resilient scabies is a serious
issue for the health of many communities. Examining scabies mite’s response to
various stimuli can help recognize a more useful and available medication to aid
reduction in the development of this resilience. The data shown in this evaluation
confirms that TTO could be an active agent for the curing of scabies, as shown by
the quick in vitro killing time seen.
Kirby Bauer method (disk diffusion). Kirby-Bauer disk diffusion is
used to analyse the sensitivity of various bacteria to different kinds of
antibiotics. It makes use of antibiotic-comprising disks and tests whether specific
microorganisms are susceptible to certain antibiotics or not. In this circumstance
the disks would contain TTO instead of an antibiotic. Initially, an
unadulterated culture of bacteria is obtained from a patient. After this, a
recognized quantity of bacteria is left to develop overnight on agar plates in
the company of a slim disc that comprises a recognized quantity of a suitable antibiotic
(TTO). If the microorganisms are vulnerable to the specific antibiotic, a zone of
clear media where microorganisms are unable to replicate borders the disc,
which is recognized as the region of inhibition. A greater region of inhibition
around an antibiotic-comprising discus shows that the microorganisms are additionally
sensitive to the antibiotic in that specific disk. According to an analysis carried
out by Carson et al. 1995, all 66 isolates of Staphylococcus aureus tested were
susceptible to TTO in disc diffusion methods. Of the isolates examined, 64 were
MRSA and 33 were mupirocin-resistant. The smallest inhibitory strength and the
smallest bactericidal strength for 60 isolates were 0-25% and 0-50%,
correspondingly. Similar effects were gotten by peers using similar means.
These in-vitro outcomes propose that tea tree oil could be beneficial in the handling
Agar Well diffusion. Classically,
an antibiotic is smeared on a well that is cut into the agar. Therefore, the
antibiotic will incline to transfer from this area of greater concentration to
the nearby area of lesser antibiotic concentration. The more antibiotic
material present in the well, the larger the zone of diffusion will be. This dispersal
is the foundation of the agar diffusion assay developed in 1944. A microbial suspension
is applied on the exterior of the agar. Next, antibiotic is smeared on a sum of
wells in the plate. There may be various strengths of a solitary antibiotic or
a sum of various antibiotics. After a period of time to allow for progression of
the microorganisms, the agar is then inspected. If microbial development is up
to the top of antibiotic comprising well, then the microbial strain is thought to
be resilient to the antibiotic. If a clearing around the antibiotic well is
present, then the microorganisms have been unfavourably affected by the
antibiotic. The scope of the inhibition region can be calculated and compared
to standard criteria, in order to govern whether the microbial strain is susceptible
to the antibiotic. Thomsen et al. 2011 conducted an analysis to examine the
antimicrobial action of a variety of commercially obtainable TTO merchandise.
One technique used was the agar well diffusion assay. The region of clearance
dimensions varied from 0 to 49.8 mm, with the additionally sticky and
lipophilic merchandises creating the smallest regions. Assumptions taken from
the study were that in general, the commercially obtainable sterile TTO
products presented antimicrobial activity that was equivalent to, or greater
than the non-formulated TTO control.
In vivo testing
refers to testing in the living organism. For example, an experiment that is
done in vivo is done in the body of a living organism as opposed to in a
laboratory method that does not use the living organism as the host of the
test. In vivo is the opposite of in vitro and can be either animal or human.
Human in vivo testing is known as clinical trials.
et al. 2006 carried out an in vivo investigation to determine the activity of terpinen-4-ol,
against human pathogenic Candida
species. Oophorectomized, rats under estrogenic treatment were used for
experimental vaginal infection with various strains of C. albicans that were resistant to forms of antifungal treatment.
The result of this rat vaginal model was that terpinen-4-ol was as active as
TTO in accelerating clearance from the vagina of all Candida strains examined.
This is the first in vivo demonstration that proves that terpinen-4-ol could
control C. albicans vaginal
infections. The purified compound holds promise for the treatment of vaginal
candidiasis, and particularly the azole-resistant forms.
clinical efficacy of TTO is under the subject of investigation. Early clinical
studies attempting to characterize the clinical efficacy of TTO are not
considered scientifically valid by today’s standards. Therefore more in vivo
trials need to be carried out to prove the efficacy of the oil and how it can
be as efficient if not more successful and with less side effects than most
One of the first rigorous clinical studies assessed the
efficacy of 5% TTO in the treatment of acne by comparing it to 5% benzoyl
peroxide (BP) (Carson et al.2006).The study found that both treatments reduced
the numbers of inflamed lesions, although BP performed significantly better
than TTO. The BP group showed significantly less oiliness than the TTO group, however
the TTO group showed significantly less scaling, itching, and dryness.
Significantly fewer overall side effects were reported by the TTO group (27 of 61
patients) than by the BP group (50 of 63 patients). This study included 124
patients suffering from mild to moderate acne and was a randomized controlled
trial (RCT). As TTO has such a distinctive odour the patients could not be
blinded, however the investigators were instead blinded. The trial lasted three
Satchell et al. 2002
carried out a trial using 5% TTO shampoo to help combat dandruff. Dandruff can
be caused by yeast like fungus known as malassezia and as previously discussed
TTO works as an antifungal. A RCT was carried out which contained 126 people
with mild to moderate dandruff. Once again it was the investigator that was
blinded due to its distinctive odour. 63 people used the 5% TTO shampoo and 62
used a placebo shampoo. The shampoo was to be used daily for four weeks. At the
end of the four weeks, 41.2% of the TTO group had a completely dandruff free
scalp in comparison with the placebo group that only 11.2% achieved results. As
well as having better results, the TTO group reported fewer adverse side
effects. Only 5% of the TTO group report cases of burning, stinging or itching
compared to 13 % in the placebo group.
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