Antimicrobial activity of essential oils

Abstract

Natural products have been studied aiming to understand their biological properties. Thus, this study aimed to investigate the antimicrobial activity of twenty-seven essential oils (EOs) used in aromatherapy procedures, a natural therapy with great emphasis currently used against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa strains. The agar dilution method was carried out and minimal inhibitory concentration against 50% and 90% of strains (MIC50% and MIC90% values) were reported. The S. aureus strains were highly susceptible with MIC90% from 0.21 mg/mL to black pepper (Piper nigrum) and tea tree (Melaleuca alternifolia) to 26.52 mg/mL with copaiba (Copaifera officinalis) EO. Cinnamon (Cinnamomum cassia) and clove (Syzygium aromaticum) EOs were effective against E. coli (2.0 mg/mL) while the S. aromaticum EO was against P. aeruginosa (8.29 mg/mL). Thus, the higher susceptibility of Gram-positive bacteria when compared with Gram-negative strains was found, and a large variability in the potential antibacterial has also been observed.

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Antimicrobial activity of essential oils
Bruna Fernanda Murbach Teles Andradea, Lidiane Nunes Barbosaa, Isabella da Silva Probsta &
Ary Fernandes Júniora
a Department of Microbiology and Immunology, Institute of Biosciences, Universidade
Estadual Paulista Júlio de Mesquita Filho-UNESP, São Paulo, Brazil
Published online: 29 Nov 2013.
To cite this article: Bruna Fernanda Murbach Teles Andrade, Lidiane Nunes Barbosa, Isabella da Silva Probst & Ary
Fernandes Júnior (2014) Antimicrobial activity of essential oils, Journal of Essential Oil Research, 26:1, 34-40, DOI:
10.1080/10412905.2013.860409
To link to this article: http://dx.doi.org/10.1080/10412905.2013.860409
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Antimicrobial activity of essential oils
Bruna Fernanda Murbach Teles Andrade, Lidiane Nunes Barbosa, Isabella da Silva Probst and
Ary Fernandes Júnior*
Department of Microbiology and Immunology, Institute of Biosciences, Universidade Estadual Paulista Júlio
de Mesquita Filho-UNESP, São Paulo, Brazil
(Received 11 July 2012; accepted 17 October 2013)
Natural products have been studied aiming to understand their biological properties. Thus, this study aimed to
investigate the antimicrobial activity of twenty-seven essential oils (EOs) used in aromatherapy procedures, a natural
therapy with great emphasis currently used against Staphylococcus aureus,Escherichia coli and Pseudomonas
aeruginosa strains. The agar dilution method was carried out and minimal inhibitory concentration against 50% and
90% of strains (MIC
50%
and MIC
90%
values) were reported. The S.aureus strains were highly susceptible with
MIC
90%
from 0.21 mg/mL to black pepper (Piper nigrum) and tea tree (Melaleuca alternifolia) to 26.52 mg/mL with
copaiba (Copaifera officinalis) EO. Cinnamon (Cinnamomum cassia) and clove (Syzygium aromaticum) EOs were
effective against E.coli (2.0 mg/mL) while the S.aromaticum EO was against P.aeruginosa (8.29 mg/mL). Thus,
the higher susceptibility of Gram-positive bacteria when compared with Gram-negative strains was found, and a large
variability in the potential antibacterial has also been observed.
Keywords: antibacterial; aromatherapy; EO; minimal inhibitory concentration
Introduction
Herbs, and their essential oils (EOs), have been used
since the beginning of human history for flavored foods
and beverages; they have been empirically used to dis-
guise unpleasant odors, attract other individuals and
control health problems, contributing to the welfare
humans and animals, thus demonstrating the cultural
and economic importance use of these products (1).
The EOs are typically liquid, clear and unusually
colored, complex and the present compounds are vola-
tile, characterized by a strong odor and synthesized by
aromatic plants during secondary metabolites, which
act to protect the plant against microorganisms and
insects. They can be synthesized in several plant organs
such as buds, flowers, leaves, stems, branches, seeds,
berries, roots, wood or bark, being stored in secretory
cells, cavities, channels, epidermal cells or trichomes
(2). Temporal and spatial variations in the total content
of secondary metabolites products from plants occur at
different levels and, despite the existence of a genetic
control, the expression may undergo changes resulting
from biochemical, physiological, ecological and evolu-
tionary interactions that represent an important interface
between chemistry and the environment surrounding
the plants (3).
As for industrial production, EOs are obtained by
steam distillation, which is on the rise in food and
pharmaceutical applications, and pressurized supercriti-
cal fluid, especially carbon dioxide (4).
EOs have several biological properties, such as lar-
vicidal action (5), antioxidant (6), analgesic and anti-
inflammatory (7), fungicide (8) and antitumor activity
(9).
The in vitro antimicrobial activity of EO has been
researched extensively against a variety of microorga-
nisms (10). Nevertheless, the emergence of multidrug-
resistant bacteria poses a challenge to treating infections,
so the need to find new substances with antimicrobial
properties for use in the fight against these microorga-
nisms is evident (11,12). Historically, most antibiotics
come from a small set of functional molecular structures
whose lives were extended by generations of synthetic
reorganizations and arrangements (13). Moreover, the
food, pharmaceutical and cosmetic industries have
shown great interest in the antimicrobial properties of
EOs, as the use of natural additives has received
importance as a trend in the replacement of synthetic
preservatives (14).
The objective was to establish in vitro the antimi-
crobial activities of EOs that are normally used in natu-
ral therapies against S.aureus,E.coli and
P.aeruginosa strains isolated from human clinical
specimens and one standard ATCC (American Type
Culture Collection) of each bacterial species; this was
*Corresponding author. Email: ary@ibb.unesp.br
© 2013 Taylor & Francis
Journal of Essential Oil Research, 2014
Vol. 26, No. 1, 34–40, http://dx.doi.org/10.1080/10412905.2013.860409
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Table 1. Density (mg/mL) and essential oils chemical compounds (%) obtained by chromatography–mass spectrometry
(GC–MS) from the supplier of the essential oils (By Samia Aromatherapy/São Paulo/Brazil).
Essential oil
Density
(mg/mL) Compounds in essential oils (%)
Bergamot (Citrus
aurantium bergamia)
871 Limonene (35.24), linalina acetate (30.40), linalool (18.45), β-pinene (5.42),
γ-terpinene (3.74), sabinene (0.92), α-pinene (0.89), myrcene (0.81), for-cymene (0.45)
Black pepper (Piper
nigrum)
846 Limoneno (23.80), δ-3-carene (21.97), α-pinene (12.89), β-caryophyllene (11.34),
β-pinene (3.91), sabinene (3.78), α-felandeno (3.76), myrcene (2.88), para-cymene
(1.38), linalool (1.24), terpinolene (1.17), β-selineno (1.11), 1.8 cineole (0.98), α-
terpinene (0.97), α-humulene (0.77), α-copaene (0.71), eugenol (0.56), terpinen-4-ol
(0.47), camphene (0.21), safrole (0.17)
Brazil’s spearmint (Mentha
arvensis)
849 Menthol (54.48), menthone (19:12), pulegone (5.57), isopulegol (2.02)
Cardamom (Elettaria
cardamomum)
869 n/d
Cedar (Cedrus atlantica) 891 Widreno (27.75), α-cedrol (22.14), α-Cedrenus (19.84), α-muuroleno (4.55), widrol
(3.79)
Cinnamon (Cinnamomum
cassia)
1008 Eugenol (72.13), eugenila acetate (3.87), β-caryophyllene (3.48), benzyl benzoate
(3.24), linalool (1.23), para-cymene (0.76), α-pinene (0.63), α-humulene (0.61),
α-phellandrene (0.49), 1.8 cineole (0.27), limonene (0.22), camphene (0.21), β-pinene
(0.21)
Clary sage (Salvia sclarea) 857 Linalina acetate (66.77), linalool (22.67), geranyl acetate (3.29), β-caryophyllene
(1.15), myrcene (0.18), limonene (0.15), 1.8 cineole (0.12)
Clove (Syzygium
aromaticum)
988 Eugenol (83.63), β-caryophyllene (12.39), alpha-humulene (3.05), eugenol acetate
(0.93)
Copaiba (Copaifera
officinalis)
884 β-Caryophyllene (44.47), β-bisabolene (8.0), germacrene B (8.0), α-copaene (7.98),
germacrene d (5.95), α-humulene (5.40), δ-cadinene (4.57)
Cypress (Cupressus
sempervirens)
840 α-Pinene (52.26), δ-3-carene, α-terpinolene (2.65), α-terpinila acetate (2.63), limonene
(2.60), myrcene (2.40), terpinen-4-ol (1.40), sabinene (1.24), β-pinene (1.14), α-tujeno
(0.96), α-fenchene (0.81), γ-terpinene (0.79), p-cymene (0.70), geranyl acetate (0.41),
α-terpinene (0.35), 1.8 cineole (0.34), camphene (0.28)
Eucalyptus (Eucalyptus
globulus)
883 1.8 Cineole (80.17), α-pinene (11.25), diacetone alcohol (4.32), p-cymene (2.28),
α-terpineol (0.85), terpinen-4-ol (0.60), β-pinene (0.53)
Fennel (Foeniculum
vulgare)
919 trans-Anethole (95.66), linalool (2.91), estragol (0.39), α-pinene (0.13)
Geranium (Pelargonium
graveolens)
848 Citronellol (31.58), geraniol (25.47), fermiato of citronelita (12.74), fermiato of
geranyl (6.71), linalool (6.33); isomenthone (4.35), rose oxide (0.89), citronelita
acetate (0.48)
Ginger (Zingiber
officinalis)
850 α-Zingiberene (22.85), curcumene (18.96), β-sesquifilandreno (13:12), β-bisabolene
(11.58), α-farnesene (4.28), camphene (1.77), β-phellandrene (1.58), 1.8 cineole (1.35),
α-pinene (0.43) trans-β-farnesene (0.30), myrcene (0.20)
Lavender (Lavandula
officinalis)
853 1.8 Cineole (45.97), p-cymene (4.19), 1-terpinen-4-ol (2.30), alpha-pinene (1.48),
limonene (1.46), gamma-terpinene (1.17), terpinolene (1.04)
Lemongrass (Cymbopogon
schoenanthus)
858 Geranial (48.57), neral (32.86), geranyl acetate (3.98), β-caryophyllene (1.59), linalool
(1.23), camphene (1.19), caryophyllene oxide (0.67), eugenol (0.48), limonene (0.23),
α-pinene (0.20), trans-β-ocimene (0.12)
Marjoram (Origanum
majorana)
841 1.8 Cineole (48.05), linalool (22.69), limonene (8.10), α-pinene (4.42), β-pinene
(4.05), isobornyl acetate (2.82), para-cymene (2.21),,estragol (1.02), γ-terpinene
(0.96), camphene (0.74), wiridiflorol (0.73), myrcene (0.51), borneol (0.49) trans-
linalool oxide (0.24), cis-linalool oxide (0.21)
Nutmeg (Myristica
fragans)
889 α-Pinene (18.35), myristicin (17.65), β-pinene (12.29), sabinene (10.15), terpinen-4-ol
(8.21), γ-terpinene (4.18), limonene (3.63), para-cymene (3.15), α-terpinolene (2.91),
safrole (2.68), 1.8 cineole (2.16), terpinolene (1.84), methyl eugenol (1.59), α-terpineol
(1.52), δ-3-carene (1.41), elemicin (0.74), eugenol (0.53)
Orange (Citrus aurantium
dulcis)
820 Limonene (96.25), myrcene (1.81), linalool (0.49), α-pinene (0.49), sabinene (0.32),
β-phellandrene (0.27)
Palmarosa (Cymbopogon
martinii)
874 Geraniol (57.49), geranyl acetate (13.56), linalool (1.71), beta-caryophyllene (1.07),
ocimene (0.27)
Patchouli (Pogostemon
patchouli)
1009 Patchoulol (25.21), δ-guaieno (11.49); gurjunene-α(11.26); seicheleno (9.61),
α-guaieno (9:56), benzyl alcohol (6.73), vidreno (3.12), aromadendrene (2.81),
α-cedrol (2.63), β-patchouleno (1.57)
(Continued )
Journal of Essential Oil Research 35
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performed by the dilution of EOs onto Mueller Hinton
agar (MHA) and the minimal inhibitory concentration
(MIC) against each and the MIC
50%
and MIC
90%
values were recorded.
Experimental
Essential oils
Twenty-seven samples of EOs, from the supplier By
Samia Aromatherapy (São Paulo-SP, Brazil) in amber
glass vials with a capacity of 10 mL, were selected
according to their frequent use in aromatherapy proce-
dures. These EOs were: bergamot (Citrus aurantium
bergamia), black pepper (Piper nigrum), Brazil’s
spearmint (Mentha arvensis), cardamom (Elettaria
cardamomum), cedar (Cedrus atlantica), cinnamon
(Cinnamomum cassia), clary sage (Salvia sclarea), clove
(Syzygium aromaticum), copaiba (Copaifera officinalis),
cypress (Cupressus sempervirens), eucalyptus (Eucalyp-
tus globulus), fennel (Foeniculum vulgare), geranium
(Pelargonium graveolens), ginger (Zingiber officinalis),
lavender (Lavandula officinalis), lemongrass (Cymbopo-
gon schoenanthus), marjoram (Origanum majorana),
nutmeg (Myristica fragans), orange (Citrus aurantium
dulcis), palmarosa (Cymbopogon martinii), patchouli
(Pogostemon patchouli), pine (Pinus sylvestris), rose-
mary (Rosmarinus officinallis), Tahiti lime (Citrus limo-
num), tea tree (Melaleuca alternifolia), vetiver (Vetiveria
zizanioides) and ylang ylang (Cananga odorata). The
samples were kept at room temperature and the chemical
characterization of the oils samples were provided by
supplier, including the gas chromatography–mass spec-
trometry (GC–MS) analysis (Table 1). Density values
from each studied oil were performed using methodology
recommended by Fonseca and Librandi (15)in
Eppendorf tubes, which were weighed (P1) on an
analytical balance and then weighed again (P2) after the
addition of 1 mL (V) of oil. The density (D) was
calculated using the formula below.
D¼
P2P1
V
¼
mg
mL
Bacterial strains
The bacterial strains from the American Type Culture
Collection (ATCC) standard strains (E.coli ATCC
25922, S.aureus ATCC 25923 and P.aeruginosa
ATCC 27853), as well as ten S.aureus, ten E.coli and
nine P.aeruginosa isolated from human clinical speci-
mens, were selected from strains stored at −80°C in the
Department of Microbiology and Immunology of Bio-
sciences Institute of UNESP, Botucatu-SP. Prior to use,
the strains were plated on blood agar medium to check
viability and purity, and maintained on nutrient agar for
use in bacterial susceptibility assays.
Antimicrobial activity of EOs by the agar dilution
method and MIC
Susceptibility tests for determining the MIC of EOs were
carried out following the agar dilution method, adapted
from CLSI (16) protocol, the plate discs were prepared
and antimicrobial assays were performed during one day.
Each EO was diluted alone in MHA plus 0.5% Tween
80 at 45°C in Petri dishes and equivalent concentrations
of 0.025, 0.05, 0.1, 0.2, 0.5, 0.8, 1.0, 1.5, 2.0, 2.5 and
3.0% v/v were established. The strains were grown at
35°C/18–24 hours in brain heart infusion (BHI) and
standard suspensions were performed in sterile saline
(0.85%) using scale 0.5 of MacFarland aiming a
Table 1. (Continued ).
Essential oil
Density
(mg/mL) Compounds in essential oils (%)
Pine (Pinus sylvestris) 874 Bornyl acetate (32.74), camphene (21.67), α-pinene (10.95), limonene (4.42), 1.8
cineole (3.15), borneol (3.11), β-pinene (1.82), β-caryophyllene (1.53), terpinolene
(1.01), myrcene (0.54), geranyl acetate (12:34), camphor (0.22), para-cymene (0.14),
γ-terpinene (0.12)
Rosemary (Rosmarinus
officinallis)
885 1.8 Cineole (31.57), camphor (20:42), α-pinene (15.78), camphene (4.93), limonene
(3.76), geraniol (2.43), myrcene (2.02), linalool (1.70), para-cymene (1.66), γ-terpinene
(1.14), α-terpinolene (0.99), bornyl acetate (0.41), borneol (0.15)
Tahiti lime (Citrus
limonum)
840 Limonene (62.34), γ-terpinene (11.96), β-pinene (10.23), β-bisabolene (2.68), α-pinene
(1.97), geraniol (1.84), myrcene (1.49), para-cymene (1.18), neral (1.04), trans-α-
bergamotene (1.02), α-tujeno (0.50)
Tea tree (Melaleuca
alternifolia)
858 1-Terpinen-4-ol (53.40), p-cymene (8.9), gamma-terpinene (5.34), 1.8 cineole (3.18),
alpha-pinene (1.40), terpinolene (1.05), limonene (0.70)
Vetiver (Vetiveria
zizanioides)
977 n/d
Ylang ylang (Cananga
odorata)
904 trans-β-Caryophyllene (12.92), linalool (11.38), germacrene-d (11.21), benzyl acetate
(10.34), geranyl acetate (9.87).
Note: n/d, information not obtained.
36 B.F.M.T. Andrade et al.
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bacterial concentration about 1.5 × 10
8
colony forming
units (CFU)/mL. The inoculation of thirty-two strains,
from standardized suspensions, was made using a Sterr
multi-inoculator using suspensions standardized at 0.5
MacFarland, with a second dilution performed onto BHI
to obtain inoculum of an approximate concentration of
10
5
–10
6
CFU/mL. After Petri dishes were inoculated
and incubated at 35°C/18–24 hours, bacterial growth
was assessed and the MIC values were recorded for each
strain. The conversion of values from % v/v to mg/mL,
using the density values of each oil, and their
calculations of the MIC
50%
and MIC
90%
for each tested
bacterial strains were performed.
Statistical analysis
The results obtained were used to compare three
or more independent testing treatments via the
Kruskal–Wallis test. For meaningful analysis (p≤0.001),
we apply the Student–Newman–Keuls test for multiple
comparisons tests between treatments.
Results and discussion
The research about antimicrobial activity, the action
mechanism and potential use of volatile plant oils has
received prominence in recent decades in parallel with
advances in traditional approaches to protecting the
health of humans, animals and food against the
presence of pathogenic and spoilage microorganisms.
Thus, investigations on the antimicrobial activity of
plant extracts against different pathogens have been
performed worldwide (17); our results have importance
because they provide information about this subject.
The density (mg/mL), chemical compounds and
their percentages in the total composition of the each
EO (twenty-seven samples) were found; results are
presented in Table 1. We emphasize that the data about
chemical analysis of the oils studied were received
from the company By Samia Aromatherapy who
supplied the EO samples. All of the oils studied
showed a density above 800 mg/mL, with orange oil
having the lowest value (820 mg/mL) and patchouli
(1009 mg/mL), cinnamon (1008 mg/mL) and clove
(988mg/mL) presenting the highest density values.
Although the chemical characterization of the oils plays
a role in studies of this nature, according to some
authors, it cannot be concluded that the major compo-
nent is the biologically active compound of this study,
so the effect can be attributed to a constituent or lesser
extent a synergy between existing compounds in the oil
(18–21). In general, the EO showed diversity in their
chemical characterization, but these are in agreement
with the literature in question.
A total of twenty-seven oils were assayed by the
agar dilution method. The MIC
90%
values against bac-
terial strain tested (Table 2) show that S.aureus strains
were susceptible to a high number of EOs, and eight of
the twenty-seven oils tested showed inhibitory activity
with MIC
90%
values below 0.30 mg/mL (e.g. eucalyp-
tus, lemongrass, patchouli, black pepper, clary sage, tea
tree, vetiver, ylang ylang).
With the tests using the agar dilution methodology
at the concentrations tested, it was not possible to
achieve MIC values for P.aeruginosa strains, except
for cinnamon; these results corroborate those reported
by Hammer et al. (21), who determined the MIC
against E.coli and S.aureus but failed to find results
for P.aeruginosa strains.
Thus, the S.aureus strains showed high susceptibil-
ity to natural products, which again confirms the results
from the literature (22,23), or in other words, Gram-
positive species are more sensitive to natural products
that Gram-negative bacteria.
These data are important for the treatment of infec-
tions caused by these bacteria; S.aureus is described as
one of the main agents responsible for infection, as its
virulence and ability to acquire antimicrobial resistance
results in a serious problem throughout the world for
hospitals and health professionals (24).
Pseudomonas aeruginosa is a Gram-negative bacte-
rium that produces water-soluble pigments, which is
widely distributed in soil and water, and is a hospital
pathogen that grows in damp areas such as sinks, bath-
tubs and showers; it is also considered a resistant bacte-
rium (25). Despite the fact that E.coli is a Gram-
negative bacteria as well as P.aeruginosa, this bacte-
rium showed sensitivity to fourteen oils at the highest
concentrations tested. These results corroborate with
those reported by Duarte et al. (26), who concluded
that the C.martini (palmarosa) EO and its major com-
ponent, geraniol, may be useful for the treatment of
diarrhoea caused by E.coli.
EOs mainly include two biosynthetic groups, all
characterized by low molecular weight, including aro-
matic and aliphatic constituents, and terpenes and terpe-
noids (27).
As a typical lipophilic compound, EOs cross the cell
wall and cytoplasmic membrane and the cytotoxic
activity appears to be linked to disruption of the struc-
tures of the different layers of polysaccharides, fatty
acids and phospholipids, due to its mechanism of action
that hits multiple targets at the same time (22). Perme-
ability, composition and charge of the outer structures of
the microorganisms mainly determined these differences;
the lipophilic character of terpenes is associated with the
antimicrobial mechanism (28). Numerous reports have
been made about the mechanisms of antimicrobial action
of the oils, and some cases have been partly elucidated,
Journal of Essential Oil Research 37
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e.g. the tea tree EO (M.alternifolia) and its major
compound, terpinen-4-ol, which causes lysis and loss of
membrane integrity due to output ions and cellular
respiration inhibition (29,30).
Cypress (C.sempervirens) was the only species that
showed no antibacterial activity according the suscepti-
bility assay performed. According to Hammer et al.
(21), this oil also showed no activity against E.coli
and P.aeruginosa, although it has some effect on the
growth of strains of S.aureus with an MIC value of
2% v/v. However, the authors report that a single stan-
dard NCTC strain (National Collection of Type Cul-
tures) was used, which may explain the different results
obtained, while this study tested strains isolated from
human clinical cases, and therefore distinct phenotypes
itself. However, C.arizonica, from the same family as
C.sempervirens, has been attributed weak antimicrobial
activity for this EO because of the high hydrocarbon
content (31).
EO contain complex mixtures of components and
thus have multiple antimicrobial properties; most of this
action appears to derive from oxygenated terpenoids,
particularly phenolic terpenes, phenylpropanoids and
alcohols; other constituents, e.g. hydrocarbons that
typically showed low activities, can be used in
combinations to increase their bioactivities (27).
In general, the oils of cinnamon and clove oils were
those with the highest potential inhibitors against the
three bacterial strains used. According to Prabuseeniva-
san et al. (32), these oils were able to inhibit the
growth of both Gram-positive and Gram-negative
species. Both oils showed eugenol, i.e. phenylpropa-
noid, to be the main compound.
The clove EO exhibited the best activity among the
twenty-seven oils tested against both Gram-negative
strains, but for the strains of S.aureus, this was black
pepper oil with an MIC
90%
of 0.21 mg/mL.
Most of the EOs used in this study has terpinen-
4-ol, linalool and eugenol as part of their compounds.
The antimicrobial mechanism involved with linalool
is related to its high water solubility and to its ability
to penetrate the bacteria cell wall (33). One hypothesis
is that linalool has the potential to act as either a pro-
tein denaturing agent or as a solvent dehydrating agent,
Table 2. Minimal inhibitory concentration 50% (MIC
50%
) and 90% (MIC
90%
) (mg/mL) found on essential oils samples against
ATCC standard and Staphylococcus aureus,Escherichia coli and Pseudomonas aeruginosa strains isolated from clinical human
specimens.
Essential oil
S.aureus (n=11)*,
CIM
50%
–CIM
90%
E.coli (n=11)*,
CIM
50%
–CIM
90%
P.aeruginosa (n=10)**,
CIM
50%
–CIM
90%
Bergamot (Citrus aurantium bergamia) 10.50–19.81
w
>26.13–>26.13 >26.13–>26.13
Black pepper (Piper nigrum) 0.21–0.21
a
>25.38–>25.38 >25.38–>25.38
Brazil’s spearmint (Mentha arvensis) 1.90–2.26
l
5.52 -5.52 >25.47–>25.47
Cardamom (Elettaria cardamomum) 7.58–7.58
s
>26.07–>26.07 >26.07- >26.07
Cedar (Cedrus atlantica) 1.78–2.76
nl
22.27–26.73
k_
>26.73–>26.73
Cinnamon (Cinnamomum cassia) 1.00–1.14
ok
2.00–2.00
b
25.00 –30.0
ba
Clary sage (Salvia sclarea) 0.29–0.29
hf
>25.71–>25.71 >25.71–>25.71
Clove (Syzygium aromaticum) 0.67 -1.21
k
1.11–2.00
a
4.60–8.29
a
Copaiba (Copaifera officinalis) 24.07–26.52
z
>26.52–>26.52 >26.52–>26.52
Cypress (Cupressus sempervirens) >25.2–>25.2 >25.20–>25.20 >25.20–>25.20
Eucalyptus (Eucalyptus globulus) 0.22–0.22
c
11.00–14.35
h
>26.49–>26.49
Fennel (Foeniculum vulgare) 7.81–7.81
us
13.08–20.22
l
>27.57–>27.57
Geranium (Pelargonium graveolens) 0.20- 0.31
ge
3.90–4.24
ec
>25.40–>25.40
Ginger (Zingiber officinalis) 3.23–4.93
qp
>25.5–>25.5 >25.50–>25.50
Lavender (Lavandula officinalis officinalis) 2.37–4.27
r
21.3–25.59
mL
>25.59–>25.59
Lemongrass (Cymbopogon schoenanthus) 0.15–0.22
i
1,98–2.10
gc
>25.74–>25.74
Marjoram (Origanum majorana) 4.21–4.21
p
4.21–4.21
dc
>25.23 ->25.23
Nutmeg (Myristica fragans) 13.96–13.96
yx
18.52–18.52
j
>26.67- >26.67
Orange (Citrus aurantium dulcis) 12.50–16.5
x
>24.63–>24.63 >24.63–>24.63
Palmarosa (Cymbopogon martinii) 0.48–0.59
m
1.90–2.09
fc
>26.22- >26.22
Patchouli (Pogostemon patchouli) 0.25–0.25
f
>30.27–>30.27 >30.27–>30.27
Pine (Pinus sylvestris) 2.58–2.58
ji
>26.22–>26.22 >26.22–>26.22
Rosemary (Rosmarinus officinallis) 6.40–7.26
t
17.70–22.12
i
>26.55–>26.55
Tahiti lime (Citrus limonum) 10.0–14.91
v
>25.2–>25.2 >25.2–>25.2
Tea tree (Melaleuca alternifolia) 0.21–0.21
b
4.29–4.29
c
>25.74–>25.74
Vetiver (Vetiveria zizanioides) 0.24–0.24
e
>29.31–>29.31 >29.31–>29.31
Ylang ylang (Cananga odorata) 0.23–0.23
d
>27.12–>27.12 >27.12–>27.12
Note:*ATCC and plus ten clinical isolated; **ATCC and plus nine clinical isolated. Values preceded by ‘>’were not considered in the statistical
analysis because they did not show inhibitory capacity up to the maximum concentration tested in the trials. Different letters in columns represent
statistical differences for antibacterial activities of essential oils (mg/mL) when p≤0.001.
38 B.F.M.T. Andrade et al.
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which may also contribute to its antimicrobial activity
(34).
The antimicrobial activity of some EOs could be
explained by the significant amount of linalool, which
is an oxygenated monoterpenoid (35). Knobloch et al.
(36) related that linalool had a significantly increased
antimicrobial activity when compared to eugenol. Over-
all, the antibacterial activity of the EOs can be related
to the content of many of the compounds identified in
the oils, including eugenol (17,37).
Although linalool presents important antioxidant
and antimicrobial effects (38), it must be noted that the
antimicrobial effect of an EO depends on all of its
chemical components (35).
Thus, we concluded that P.aeruginosa strains were
highly resistant to the EOs, while the S.aureus strains
were considerably sensitive, although the potential use
of EOs can be applied to both Gram-positive and
Gram-negative bacteria.
Acknowledgements
The authors are grateful to the company By Samia Aroma-
therapy for providing the samples of essential oils as well as
by chemical analysis of the samples. Also thank Prof. Dr. Lu-
ciano Barbosa of Department of Biostatistics/Biosciences
Institute, UNESP, by statistics analysis of the results from the
study.
Conflict of interest
The authors have declared no conflict of interest
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