In vitro antibacterial activity of some plant essential oils

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BMC Complementary and
Alternative Medicine
Open Access
Research article
In vitro antibacterial activity of some plant essential oils
Seenivasan Prabuseenivasan, Manickkam Jayakumar and
Savarimuthu Ignacimuthu*
Address: Entomology Research Institute, Loyola College, Chennai – 600 034, India.
Email: Seenivasan Prabuseenivasan - prabsri@gmail.com; Manickkam Jayakumar - jaismohai@gmail.com;
Savarimuthu Ignacimuthu* - eri_lc@hotmail.com
* Corresponding author
Abstract
Background: To evaluate the antibacterial activity of 21 plant essential oils against six bacterial
species.
Methods: 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.
Results: 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.
Conclusion: 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.
Background
The spread of drug resistant pathogens is one of the most
serious threats to successful treatment of microbial dis-
eases. Down the ages essential oils and other extracts of
plants have evoked interest as sources of natural products.
They have been screened for their potential uses as alter-
native remedies for the treatment of many infectious dis-
eases [1]. World Health Organization (WHO) noted that
majority of the world's population depends on traditional
medicine for primary healthcare. Medicinal and aromatic
plants which are widely used as medicine and constitute a
major source of natural organic compounds.
Essential oils have been shown to possess antibacterial,
antifungal, antiviral insecticidal and antioxidant proper-
ties [2,3]. Some oils have been used in cancer treatment
[4]. Some other oils have been used in food preservation
[5], aromatherapy [6] and fragrance industries [7]. Essen-
tial oils are a rich source of biologically active com-
pounds. There has been an increased interest in looking at
Published: 30 November 2006
BMC Complementary and Alternative Medicine 2006, 6:39 doi:10.1186/1472-6882-6-39
Received: 29 July 2006
Accepted: 30 November 2006
This article is available from: http://www.biomedcentral.com/1472-6882/6/39
© 2006 Prabuseenivasan et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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antimicrobial properties of extracts from aromatic plants
particularly essential oils [8]. Therefore, it is reasonable to
expect a variety of plant compounds in these oils with spe-
cific as well as general antimicrobial activity and antibi-
otic potential [9].
Essential oils (also called volatile oils) are aromatic oily
liquids obtained from plant materials (flowers, buds,
seeds, leaves, twigs, bark, herbs, wood, fruits and roots).
They can be obtained by expression, fermentation or
extraction but the method of steam distillation is most
commonly used for commercial production. An estimated
3000 essential oils are known, of which 300 are commer-
cially important in fragrance market [7]. Essential oils are
complex mixers comprising many single compounds.
Chemically they are derived from terpenes and their oxy-
genated compounds. Each of these constituents contrib-
utes to the beneficial or adverse effects.
Essential oils such as aniseed, calamus, camphor, cedar-
wood, cinnamon, citronella, clove, eucalyptus, geranium,
lavender, lemon, lemongrass, lime, mint, nutmeg, orange,
palmarosa, rosemary, basil, vetiver and wintergreen have
been traditionally used by people for various purposes in
different parts of the world (Table 1). Cinnamon, clove
and rosemary oils had shown antibacterial and antifungal
activity [10]; cinnamon oil also possesses antidiabetic
property [11]. Anti-inflammatory activity has been found
in basil [12]. Lemon and rosemary oils possess antioxi-
dant property [13,14]. Peppermint and orange oils have
shown anticancer activity [15,16]. Citronella oil has
shown inhibitory effect on biodegrading and storage-con-
taminating fungi [17]. Lime oil has shown immunomod-
ulatory effect in humans [16]. Lavender oil has shown
antibacterial and antifungal activity; it was also found to
be effective to treat burns and insect bites [18].
In spite of all the information available on the 21 oils
selected for this study, we were not able to find antibacte-
rial activity for all those oils. Hence this study was under-
taken with the intention of finding out the efficacy of
these essential oils as antimicrobial agents for commercial
purposes.
Methods
Essential oils
Twenty-one essential oils obtained from Tegraj & Co (P)
Ltd, India (commercial producers of plant essential oils
and aromatic substances) were used in this study (Table
1). These oils were selected based on literature survey and
their use in traditional medicine. Quality of the oils was
ascertained to be more than 98% pure.
Test organism
Microorganisms were obtained from the Department of
Microbiology, Christian Medical College, Vellore, India
and Institute of Basic Medical Sciences (IBMS), Chennai,
India. Four strains of gram-negative bacteria [Escherichia
coli (ATCC 25922), Klebsiella pneumoniae (ATCC 15380),
Pseudomonas aeruginosa (ATCC 27853), Proteus vulgaris
(MTCC 1771)] and two strains of gram-positive bacteria
[Bacillus subtilis (MTCC 441) and Staphylococcus aureus
Table 1: List of selected essential oils and their properties.
Common name Botanical name (Family) Properties [37, 42, 43]
Aniseed oil Pimpinella anisum (Umbelliferae) Carminative, stimulant, expectorant, condiment and flavouring agent.
Calamus oil Acorus calamus (Araceae) Carminative, bitter stimulant, vermifuge and insect repellent
Camphor oil Cinnamomuum camphora (Lauraceae) Rubefacient, tooth powder and cosmetic agent.
Cedarwood oil Cedrus atlantica (Coniferae) Antiseptic, astringent, diuretic, fungicidal, sedative and stimulant.
Cinnamon oil Cinnamomum zeylanicum (Lauraceae) Carminative, stomachic, astringent, stimulant and antiseptic.
Citronella oil Cymbopogon nardus (Gramineae) Perfumery, mosquito repellent and flavouring agent.
Clove oil Eugenia caryophyllus (Myrtaceae) Dental analgesic, carminative, stimulant and antiseptic.
Eucalyptus oil Eucalyptus globulus (Myrtaceae) Counter-irritant, antiseptic, expectorant, cough reliever.
Geranium oil Pelargonium graveolens (Geraniaceae) Flavouring agent and stimulant.
Lavender oil Lavandula angustifolia (Labiatae) Stimulant and flavouring agent.
Lemon oil Citrus limon (Rutaceae) Carminative, stimulant, perfuming and flavouring agent.
Lemongrass oil Cymbopogon citratus (Graminae) Flavouring agent, antiseptic and deodorant.
Lime oil Citrus aurantium (Rutaceae) Stomachic, carminative and flavouring agent.
Nutmeg oil Myristica fragrans (Myristicaceae) Stimulant, anti rheumatic and carminative.
Orange oil Citrus sinensis (Rutaceae) Stomachic, carminative and flavouring agent.
Palmarosa oil Cymbopogon martini (Graminae) Cosmetic, anti rheumatism and insect repellent.
Peppermint oil Mentha piperita (Labiatae) Digestent, stimulant and tonic.
Rosemary oil Rosmarinus officinalis (Labiatae) Carminative, stimulant and flavouring agent.
Basil oil Ocimum sanctum (Labiatae) Antibacterial, insecticidal, stimulant, stomachic and diaphoretic.
Vetiver oil Vetiveria zizanioides (Graminae) Stimulant, refrigerant, flavouring agent, stomachic and fixative.
Wintergreen oil Gaultheria fragrantissima (Ericaceae) Irritant, vermicide agent and flavouring agent.

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(ATCC 25923)] were used. The cultures of bacteria were
maintained in their appropriate agar slants at 4°C
throughout the study and used as stock cultures.
Antibacterial assay
Screening of essential oils for antibacterial activity was
done by the disk diffusion method, which is normally
used as a preliminary check and to select between efficient
essential oils [2]. It was performed using an 18 h culture
at 37°C in 10 ml of Mueller Hinton Broth. The cultures
were adjusted to approximately 105CFU/ml with sterile
saline solution. Five hundred microliters of the suspen-
sions were spread over the plates containing Mueller-Hin-
ton agar using a sterile cotton swab in order to get a
uniform microbial growth on both control and test plates.
The essential oils were dissolved in 10% aqueous dimeth-
ylsulfoxide (DMSO) with Tween 80 (0.5% v/v for easy dif-
fusion) and sterilized by filtration through a 0.45 μm
membrane filter. Under aseptic conditions, empty steri-
lized discs (Whatman no. 5, 6 mm dia) were impregnated
with 50 μL of different concentrations (1:1, 1:5, 1:10,
1:20) of the respective essential oils and placed on the
agar surface [19]. Paper disc moistened with aqueous
DMSO was placed on the seeded petriplate as a vehicle
control. A standard disc containing streptomycin (25 μg/
disc) was used as reference control. All petridishes were
sealed with sterile laboratory parafilm to avoid eventual
evaporation of the test samples. The plates were left for 30
min at room temperature to allow the diffusion of oil, and
then they were incubated at 37°C for 18 h (18 h was fixed
as the optimum since there was no change in the inhibi-
tion up to 24 h) After the incubation period, the zone of
inhibition was measured with a calliper. Studies were per-
formed in triplicate, and mean value was calculated. The
means were analysed by one way analysis of variance
(ANOVA) followed by Tukey's post hoc multiple compar-
ison test using SPSS software package version 13.0 for
windows. The results were expressed as mean ± SD. P val-
ues <0.05 were considered as significant.
MIC assay
Based on the previous screening seven essential oils (Cin-
namon, clove, geranium, lemon, lime, orange and rose-
mary oils) were identified to have potent antibacterial
activity and their Minimum Inhibitory Concentrations
(MIC) were determined. The agar dilution method recom-
mended by the National Committee for Clinical Labora-
tory Standards [20] was used with the following
modification; a final concentration of 0.5% (v/v) Tween-
20 (Sigma) was incorporated into the agar medium to
enhance oil solubility. A series of two fold dilution of each
oil, ranging from 0.2 to 25.6 mg/ml, was prepared in
Muellur Hinton agar at 48°C. Plates were dried at room
temperature for 30 min prior to spot inoculation with 3 μl
aliquots of culture containing approximately 105 CFU/ml
of each organism. Inoculated plates were incubated at
37°C for 18 h and the MIC was determined. Experiments
were carried out in triplicate. Inhibition of bacterial
growth in the plates containing test oil was judged by
comparison with growth in blank control plates. The
MICs were determined as the lowest concentration of oil
inhibiting visible growth of each organism on the agar
plate [21].
Gas chromatography mass spectrometry (GC/MS)
The most potent oil, (cinnamon oil) was analysed using
GC/MS (Shimadzu capillary GC-quadrupole MS system
QP 5000) with two fused silica capillary column DB-5 (30
μm, 0.25 mm i.d, film thickness 0.25 μm) and a flame
ionization detector (FID) which was operated in EI mode
at 70 eV. Injector and detector temperatures were set at
220°C and 250°C, respectively. One microliter essential
oil solution in hexane was injected and analyzed with the
column held initially at 60°C for 2 min and then
increased by 3°C/min up to 300°C. Helium was
employed as carrier gas (1 ml/min). The relative amount
of individual components of the total oil is expressed as
percentage peak area relative to total peak area. Qualita-
tive identification of the different constituents was per-
formed by comparison of their relative retention times
and mass spectra with those of authentic reference com-
pounds, or by retention indices (RI) and mass spectra.
Results
The anti-bacterial activity of twenty-one selected essential
oils against six bacterial species is summarized in Table 2
and 3. The results revealed that the selected essential oils
showed antibacterial activity with varying magnitudes.
The zone of inhibition above 7 mm in diameter was taken
as positive result. Generally most of the tested organisms
were sensitive to many of the essential oils. Out of 21
essential oils tested, 19 showed antibacterial activity
against one or more bacteria. Cinnamon oil, lime oil,
geranium oil, rosemary oil, orange oil, lemon oil and
clove oil showed maximum activity against all the bacte-
rial species tested. On the other hand, aniseed oil, euca-
lyptus oil and camphor oil failed to inhibit any of the
tested strains. Both gram-positive and gram-negative bac-
teria were sensitive to the potent essential oils. P. aerugi-
nosa and P. vulgaris were inhibited by 19 oils, followed by
B. subtilis (18 oils), S. aureus (14 oils), E. coli (12 oils) and
K. pneumoniae (9 oils). In general cinnamon oil showed
significant inhibitory effect against P. aeruginosa (33.3
mm), B. subtilis (29.9 mm), P. vulgaris (29.4 mm), K. pneu-
moniae (27.5 mm) and S. aureus (20.8 mm). Moderate
effects were seen in lime oil, clove oil and lemon oil. No
obvious difference in susceptibility was found between
gram-negative and gram-positive bacteria. There was no
inhibition of growth with the vehicle control (10%
DMSO).

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Table 2: Antimicrobial activity of 21 essential oils against S. aureus, B. subtilis and K. pneumoniae using disc diffusion method
Oil Name S. aureus B. subtilis K. pneumoniae
Concentration 1:1 1:5 1:10 1:20 1:1 1:5 1:10 1:20 1:1 1:5 1:10 1:20
Aniseed oil - - - - 12.1 ± 1.0klm 10.8 ± 0.2ij - -----
Calamus oil - - - - 17.9 ± 0.9def 14.7 ± 0.5cd 12.6 ± 0.5 c11.3 ± 1.2d----
Camphor oil - - - - - - - - 8.5 ± 0.5e---
Cedar wood - - - - 13.4 ± 0.5jkl 12.2 ± 0.5ghi 99 ± 0fg -----
Cinnamon oil 20.8 ± 0.5 a18.7 ± 0.2a14.8 ± 0.2b13.7 ± 0.28b29.9 ± 0.7 a27.8 ± 1.1 a24.1 ± 1.1 a22.8 ± 0.2b27.5 ± 0.5a23.5 ± 0.5a20.9 ± 0.2a18.6 ± 0.5a
Citronella oil 15.8 ± 0.3bc 10.3 ± 0.5de - - 14.6 ± 0.5ij 12.5 ± 0.5ghi 10.3 ± 0.5de 9.3 ± 0.5ef ----
Clove oil 16.3 ± 0.5 b14.0 ± 0bc 8.1 ± 1.1d9.8 ± 0.57c14.5 ± 0.2hij 13.1 ± 0.2ef 10.1 ± 1.0def 8.9 ± 0.2f16.2 ± 0.5c14.4 ± 0.5b8.4 ± 0.5c-
Eucalyptus oil - - - - - - - -----
Geranium oil 10.4 ± 0.5e8.9 ± 0.2e- - 17.2 ± 0.2defg 14.7 ± 0.5cde - - 10.8 ± 0.2d9 ± 0c--
Lavender - - - - 12.5 ± 0.4jk 11.1 ± 0.2hi - -----
Lemon oil 17.5 ± 1.1b14.5 ± 0.2b8.3 ± 0.2d- 16.9 ± 0.2efgh 14.5 ± 0.5cdef 8.9 ± 0.5 g- 16.5 ± 0.5c15.3 ± 1.1b8.7 ± 0.5c-
Lemongrass oil 11.4 ± 1.0 de 8.9 ± 0.2e- - 16.7 ± 0.5fghi 15.1 ± 0.7 c8.9 ± 1.0fg - 8.3 ± 0.5e---
Lime oil 14.2 ± 0.5cd 12.7 ± .2bcd 10.3 ± 0. 9 ± 0.00c23.9 ± 1.1 c20.8 ± 0.7 b15.8 ± 0.2 b14.1 ± 1.1c16.1 ± 1.1c14.6 ± 0.5b12.9 ± 0.5b12.6 ± 0.5b
Nutmeg 11.7 ± 0.8de 9.1 ± 0.2e- - 11.5 ± 0.5mn 10.9 ± 0.2hij - -----
Orange oil 12.8 ± 0.2cd 10.6 ± 0.2cde - - 18.6 ± 0.8de 15.7 ± 1.2 c 9.4 ± 0.5efg 10.6 ± .5e11.9 ± 0.7d9.31.1c--
Palmarosa oil 12.5 ± 0.2cd 10.9 ± 0.5de 8 ± 0d- 15.4 ± 0.5ghi 14.2 ± 1cdef 12.5 ± 0.4 c11.3 ± 0.5d----
Peppermint oil 8.1 ± 0.5f- - - 10.6 ± 0.5mn 8.6 ± 0.4k- -----
Rosemary oil 12.5 ± 1d10.6 ± 1.0e8.6 ± 0.2d- 14.7 ± 1hi 12.8 ± 0.5efg 11.2 ± 0.5cd 8.9 ± 0.2f11.9 ± 0.5d9.9 ± 0.7c--
Basil oil 10.3 ± 0.5e8.3 ± 0.5e- - - - - -----
Vetiver oil - - - - 18.9 ± 0.9 d15.6 ± 0.5c12.8 ± 0.2 c11.6 ± 0.7d----
Wintergreen 8.7 ± 0.51f- - - 9.9 ± 0.5 n9.1 ± 0.1jk - -----
Streptomycin** 20.9 ± 0.5 26.9 ± 0.5 20.9 ± 0.9
Vehicle control - - -
** Streptomycin disc (25 μg) as a positive reference standard; Values are mean inhibition zone (mm) ± S.D of three replicates
Means within a column followed by different letters are statistically significant by tukey's test at p = 0.05; - no activity.

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Table 3: Antimicrobial activity of 21 essential oils against P. vulgaris, P. aeruginosa and E. coli using disc diffusion method
Oil Name P. vulgaris P. aeruginosa E. coli
Concentration 1:1 1:5 1:10 1:20 1:1 1:5 1:10 1:20 1:1 1:5 1:10 1:20
Aniseed oil - - - - - - ------
Calamus oil 11.1 ± 0.7gh 9.2 ± 0.5h- - 13.8 ± 0.5ef 12.8 ± 0.4f9.2 ± 0.7 d8.3 ± 0.5 d----
Camphor oil 8.8 ± 0.7 hi - - - 10 ± 0.5gh ---8.8 ± 1
d---
Cedar wood 14.1 ± 1.1f12.9 ± 0.5g8.2 ± 0.5f- 15.6 ± 0.5de 14.1 ± 0.9ef 8.23 ± 0.5d-----
Cinnamon oil 29.4 ± 0.5a27 ± 0a18.6 ± 1.52a14.1 ± 0.4b33.3 ± 1.6a32.2 ± 0.5a24.4 ± 0.5a21 ± 0a29.8 ± 0.7a26 ± 1a23.8 ± 1a21 ± 0.2a
Citronella oil 19.5 ± 0.5cd 11.3 ± 0.7g- - 12.1 ± 0.5fg 10.4 ± 0.5g------
Clove oil 20.1 ± 1c18.2 ± 0.5d11.8 ± 0.5d8 ± 0e17.4 ± 0.7d15.5 ± 0.2e8.5 ± 0.5d- 17.4 ± 2c15.1 ± 0.5c10.8 ± 0.5e8 ± 0c
Eucalyptus oil - - - - - - - - 8.5 ± 1d---
Geranium oil 19 ± 0.2de 14.6 ± 0.2e11 ± 1.5ef 8.3 ± 0e21.5 ± 0.2c19.2 ± 1.2d9.4 ± 0.5d- 14.1 ± 1c10.4 ± 1d--
Lavender 10.8 ± 0.5ghi 9.3 ± 0.5h- - 12.1 ± 0.9fg 9.9 ± 0.7g------
Lemon oil 22.5 ± 0.5b18.9 ± 0.5d15.5 ± 0.5c10.7 ± 0.2d21.4 ± 1.1c19.9 ± 0.7cd 9.1 ± 0.2d- 21.6 ± 0.5b18.9 ± 0.5b10.6 ± 0.2e-
Lemongrass oil 14.6 ± 0.7f12.1 ± 0.2g9.5 ± 0.5ef - 23.4 ± 1c19.6 ± 0.5d9.1 ± 0.5d-----
Lime oil 27.8 ± 0.5a24 ± 0b17.9 ± 0.1ab 13 ± 1c25.5 ± 1b23.5 ± 0.5b13.6 ± 0.7c9.3 ± 0.8c22.7 ± 0.5b18.9 ± 1b15.6 ± 0.5c17.6 ± 1.5b
Nutmeg 14.5 ± 0.7f11.9 ± 0.2g8 ± 0 f- 15.5 ± 0.5de 12.9 ± 1f------
Orange oil 23.7 ± 0.7b22.2 ± 0.7 c16.5 ± 0.2bc 10.7 ± 0.5d21.6 ± 0.2c18.8 ± 0.2d9.4 ± 0.5d- 22.9 ± 0.5b19.4 ± 0.7b12.4 ± 0.2d-
Palmarosa oil 19 ± 0cd 15.8 ± 0.2 e9.9 ± 0.2 def - 14.4 ± 0.5ef 13.2 ± 0.5ef 9.2 ± 0.2d-8.2 ± 0.5
d---
Peppermint oil 8.5 ± 0.2i- - - 13.4 ± .52ef 11.2 ± 0.8g------
Rosemary oil 17.4 ± 1cd 15.9 ± 0.5ef 9.7 ± 0de - 23.4 ± 0.2c21.9 ± 0.5c14.5 ± 0.5b8.3 ± 0.5d17.5 ± 1c15.1 ± 0.7c9.1 ± 0.2f-
Basil oil 8.9 ± 0.7ghi - - - 8.23 ± 0.5h- - - 10.5 ± 0.5d8.2 ± 0.5e--
Vetiver oil 11.5 ± 0.5g10.3 ± 0.2 11.4 ± 0.5de - 13.5 ± 0.5ef 11.7 ± 0.5g8.2 ± 0.2d-----
Wintergreen 15.8 ± 0.7ef 14.8 ± 0.5 f9.5 ± 1 def - 10.2 - - - 8.9 ± 1d---
Streptomycin** 18.4 ± 0.7 16.4 ± 0.2 21.2 ± 0.1
Vehicle control - - -
** Streptomycin disc (25 μg) as a positive reference standard; Values are mean inhibition zone(mm) ± S.D of three replicates
Means within a column followed by different letters are statistically significant by tukey's test at p = 0.05; - no activity.

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Minimum inhibitory concentration (MIC) for selected
seven oils ranged from 0.8 to 12.8 mg/ml (Table 4). This
study revealed that cinnamon oil showed maximum activ-
ity with MIC values ranging from 0.8 to 3.2 mg/ml fol-
lowed by clove oil with MIC values ranging from 1.6 to
6.4 mg/ml against all the tested strains where as remain-
ing oils showed moderate MIC values.
GC/MS analysis of cinnamon oil identified thirty-eight
phytochemicals as constituents; of these cinnamaldehyde
was the major compound (52.4%) followed by Benzalde-
hyde (12.31%), benzoic acid (8.20%) and benzyl alcohol
(2.23%). Remaining chemical compounds were in trace
amounts. The major components and their retention
times are summarized in Table 5.
Discussion
Plant essential oils and extracts have been used for many
thousands of years [22], in food preservation, pharmaceu-
ticals, alternative medicine and natural therapies [23,24].
It is necessary to investigate those plants scientifically
which have been used in traditional medicine to improve
the quality of healthcare. Essential oils are potential
sources of novel antimicrobial compounds [25] especially
against bacterial pathogens. In vitro studies in this work
showed that the essential oils inhibited bacterial growth
but their effectiveness varied. The antimicrobial activity of
many essential oils has been previously reviewed and clas-
sified as strong, medium or weak [26].
In our study, cinnamon, clove, geranium, lemon, lime,
orange and rosemary oils exhibited strong activity against
the selected bacterial strains. Several studies [27,28] have
shown that cinnamon, clove and rosemary oils had strong
and consistent inhibitory effects against various patho-
gens. Even though earlier studies have reported better
antimicrobial activity for eucalyptus oil [29,30] our study
showed least inhibitory activity of eucalyptus in addition
to aniseed and camphor oils. Among all oils analyzed in
this work, the essential oil of cinnamon was the most
effective as an antibacterial agent. The antibacterial activ-
ity has been attributed to the presence of some active con-
stituents in the oils. Our GC-MS study revealed
cinnamaldehyde to be the major constituent of cinnamon
oil. Cinnamaldehyde was the predominant active com-
pound found in cinnamon oil [31,32]. Earlier studies sug-
gested that the antibacterial activity of cinnamon oil was
probably due to their major component, cinnamaldehyde
and their properties could be multiple. Cinnamaldehyde
is a natural antioxidant and the animal studies suggest
that an extract of cinnamon bark taken orally may help
prevent stomach ulcer [33]. Cinnamaldehyde was com-
pletely inhibiting both sensitive and resistant stain of
Helicobacter pylori [34]. Cinnamon oil was not harmful
when consumed in food products and it inhibited the
growth of molds, yeast and bacteria [27]. Cinnamon
extract had a regulatory role in blood glucose level and
lipids and it may also exert a blood glucose-suppressing
effect [35]. The use of commercial cinnamon preparation
produced an improvement of oral candidiasis of HIV-
infected patients [36]. Cinnamon oil is locally applied
with much benefit in neuralgia and headache. As an anti-
septic it is used as an injection in gonorrhea; as germicide
it is used internally in typhoid fever. This oil is also used
in the treatment of cancer and other microbial diseases
[37]. It can be incorporated into creams, lotions, drops,
etc. which are applied externally on the body to treat dis-
eases caused by Aspergillus niger [38].
An important characteristic of essential oils and their
components is their hydrophobicity, which enable them
to partition the lipids of the bacterial cell membrane and
mitochondria, disturbing the cell structures and rendering
them more permeable [39,40]. Extensive leakage from
bacterial cells or the exit of critical molecules and ions will
lead to death [41]. Gram-positive bacteria were more
resistant to the essential oils than gram-negative bacteria
[26]. In the present study, cinnamon, lime, geranium,
rosemary, orange, lemon and clove oils were found to be
equally effective against both gram-positive and gram-
negative organisms.
Conclusion
From this study it can be concluded that many essential
oils possess antibacterial activity. Cinnamon oil has the
most potential bactericidal properties. We believe that the
present investigation together with previous studies pro-
vide support to the antibacterial properties of cinnamon
Table 4: Minimum Inhibitory Concentration (MIC) of selected essential oils (mg/ml).
Oil name S. aureus B. subtilis K. pneumoniae P. vulgaris P. aeruginosa E. coli
Cinnamon oil 3.2 >1.6 3.2 >1.6 >0.8 >1.6
Clove oil>6.4>3.2>6.4>3.2>1.6>1.6
Geranium oil >12.8 >6.4 12.8 >12.8 >12.8 >6.4
Lemon oil >12.8 >12.8 >12.8 >6.4 12.8 >6.4
Lime oil12.8>6.4>6.4>3.2>6.4>6.4
Orange oil >12.8 >12.8 12.8 >6.4 >12.8 >12.8
Rosemary oil >12.8 >6.4 >12.8 >6.4 >6.4 >6.4

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oil. It can be used as antibacterial supplement in the
developing countries towards the development of new
therapeutic agents. Additional in vivo studies and clinical
trials would be needed to justify and further evaluate the
potential of this oil as an antibacterial agent in topical or
oral applications.
Competing interests
The author(s) declare that they have no competing inter-
ests.
Authors' contributions
SP and MJ have carried out the experimental part such as
selection of essential oils, inoculum preparation and anti-
microbial evaluation. SI supervised the work, evaluated
the results and corrected the manuscript for publication.
All authors read and approved the final manuscript.
Acknowledgements
We thank ICMR, New Delhi for providing financial support. We also thank
the Department of Microbiology, Institute of Basic Medical Sciences (IBMS),
University of Madras, Chennai and Christian Medical College, Vellore, India
for providing the bacterial cultures. We are thankful to Mr. Sankar AGM, R
& D Section, Nicholas Piramal India Limited, Chennai for helping in GC/MS
analysis.
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