Molecules 2010, 15, 3200-3210; doi:10.3390/molecules15053200
Activities of Ten Essential Oils towards Propionibacterium acnes
and PC-3, A-549 and MCF-7 Cancer Cells
Yuangang Zu 1,2,†, Huimin Yu 3,†, Lu Liang 1,2, Yujie Fu 1,2,*, Thomas Efferth 4, Xia Liu 1,2 and
Nan Wu 1,2
1 Key Laboratory of Forest Plant Ecology, Ministry of Education, Northeast Forestry University,
Harbin 150040, China; E-Mails: firstname.lastname@example.org (Y.Z.); email@example.com (L.L.);
firstname.lastname@example.org (X.L.); email@example.com (N.W.)
2 Engineering Research Center of Forest Bio-preparation, Ministry of Education, Northeast Forestry
University, Harbin 150040, China
3 Chinese Medicine Department, The Second Hospital of Harbin Medical University, Harbin 150086,
China; E-Mail: firstname.lastname@example.org (H.Y.)
4 Department of Pharmaceutical Biology, Institute of Pharmacy, University of Mainz, 55099 Mainz,
Germany; E-Mail: email@example.com (T.E.)
† These authors contributed equally to this work.
* Author to whom correspondence should be addressed; E-Mail: firstname.lastname@example.org;
Received: 25 February 2010; in revised form: 20 April 2010 / Accepted: 20 April 2010 /
Published: 30 April 2010
Abstract: Ten essential oils, namely, mint (Mentha spicata L., Lamiaceae), ginger
(Zingiber officinale Rosc., Zingiberaceae), lemon (Citrus limon Burm.f., Rutaceae),
grapefruit (Citrus paradisi Macf., Rutaceae), jasmine (Jasminum grandiflora L.,
Oleaceae), lavender (Mill., Lamiaceae), chamomile (Matricaria chamomilla L.,
Compositae), thyme (Thymus vulgaris L., Lamiaceae), rose (Rosa damascena Mill.,
Rosaceae) and cinnamon (Cinnamomum zeylanicum N. Lauraceae) were tested for their
antibacterial activities towards Propionibacterium acnes and in vitro toxicology against
three human cancer cell lines. Thyme, cinnamon and rose essential oils exhibited the best
antibacterial activities towards P. acnes, with inhibition diameters of 40 ± 1.2 mm, 33.5 ±
1.5 mm and 16.5 ± 0.7 mm, and minimal inhibitory concentrations of 0.016% (v/v),
0.016% (v/v) and 0.031% (v/v), respectively. Time-kill dynamic procedures showed that
Molecules 2010, 15
thyme, cinnamon, rose, and lavender essential oils exhibited the strongest bactericidal
activities at a concentration of 0.25% (v/v), and P. acnes was completely killed after 5 min.
The thyme essential oil exhibited the strongest cytotoxicity towards three human cancer
cells. Its inhibition concentration 50% (IC50) values on PC-3, A549 and MCF-7 tumor cell
lines were 0.010% (v/v), 0.011% (v/v) and 0.030% (v/v), respectively. The cytotoxicity of
10 essential oils on human prostate carcinoma cell (PC-3) was significantly stronger than
on human lung carcinoma (A549) and human breast cancer (MCF-7) cell lines.
Keywords: essential oils; activities; Propionibacterium acnes; cytotoxicity; cancer cell lines
During recent years, plant essential oils have come more into the focus of phytomedicine [1,2].
Their widespread use has raised the interest of scientists in basic research of essential oils. Especially,
the anti-microbial and anti-oxidant activities of essential oils as well as their potential anti-cancer
activity have been investigated in recent years [3,4].
Acne is an inflammatory chronic disease, whose clinical presentation can range from a mild
comedonal form to severe cystic acne of the face, chest, and back. Factors which contribute to the
development of acne include hormonal imbalance, bacterial infection, stress, food, or cosmetic
application . Propionibacterium acnes is a Gram-positive, anaerobic microorganism, which has
been most recognized as a key factor for the development of acne . For many years antibiotics and
hormones were usually applied to treat acne [7,8]. However, these agents are often accompanied by
severe side effects and drug resistance [9,10]. Therefore, phytotherapeutic approaches with high anti-
bacterial activity and without side effects have been extensively studied as an alternative. In this
context, essential oils extracted from herbs have also been investigated for the treatment of acne .
Standard cancer chemotherapy is frequently compromised by the development of drug resistance
and unwanted, partly life-threatening side effects. There is, therefore, an urgent need for novel
treatment options with improved features. Interestingly many plant-derived compounds, i.e., paclitaxel,
vinblastine, or vincristine, and semi-synthetic derivatives of natural products, i.e., etoposide and
teniposide, are used as anti-cancer drugs. As pointed out recently, natural products from medicinal
plants represent a fertile ground for the development of novel anticancer agents .
Interestingly essential oils from some herbs and spices possess both anti-bacterial and cancer
chemopreventive activities . In previous studies, 10 essential oils including mint, ginger, lemon,
grapefruit, jasmine, lavender, chamomile, thyme, rose and cinnamon showed good pharmacological
activity [14–20]. In the present study, the anti-bacterial activities of a panel of 10 essential oils towards
P. acnes was investigated by the disc diffusion and broth dilution methods as well as detection of
dynamic bactericidal processes. Furthermore, we analyzed the cytotoxicity of these 10 essential oils
against the human cancer lines, A549, PC-3 and MCF-7, by means of the MTT (3-(4,5)-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.
Molecules 2010, 15
2. Results and Discussion
2.1. Anti-bacterial activity
We first analyzed the anti-bacterial activities of essential oils towards P. acnes. The data obtained
from the disc diffusion method indicated that thyme essential oil exhibited the strongest inhibitory
activities. The inhibition zone diameter measured was 40.0 ± 1.2 mm. Cinnamon essential oil also
possessed considerable antibacterial activity, and the inhibition diameter determined was 33.5 ± 1.5 mm.
Jasmine essential oil exhibited the lowest inhibitory activity (Figure 1). The results of minimum
inhibitory concentrations (MICs) revealed that the thyme, cinnamon and rose essential oils exhibited
the best anti-bacterial activities towards P. acnes. The MIC values were 0.016% (v/v), 0.016% (v/v)
and 0.031% (v/v), respectively (Table 1). The anti-bacterial activity of jasmine essential oil was lower
than that of other essential oils, and its minimum bactericidal concentration (MBC) was 0.5% (v/v).
The MBC values of all 10 essential oils were comparable to their corresponding MIC
values (Table 1).
Figure 1 1. Inhibition diameters of 10 essential oils towards P. acnes.
Table1. Minimal inhibitory concentrations (MICs, %v/v) and minimal bactericidal
concentrations (MBCs, %v/v) of 10 essential oils towards P. acnes.
Molecules 2010, 15
2.2. Time-kill curves
The time-kill curves of the 10 essential oils are shown in Figure 2. Rose, cinnamon, thyme, and
lavender essential oils exhibited the strongest bactericidal activities at a concentration of 0.25% (v/v);
the bacteria were completely killed within 5 min. The bactericidal activities of the other essential oils
decreased in the order: chamomile > grapefruit = lemon > ginger > mint > jasmine. The bacteria were
completely killed after 20 min by chamomile essential oil, 30 min by grapefruit and lemon essential
oils, and 45 min by ginger essential oil. However, mint essential oil did not kill bacteria even after
120 min. The jasmine essential oil exhibited the lowest bactericidal activity, and the number of
P.acnes still retained 105 CFU/mL after 120 min.
Figure 2. Time-kill curves of 10 essential oils (0.25% v/v) towards P.acnes in 2h.
(A): essential oils of mint, ginger, rose, cinnamon, and grapefruit; (B): essential oils of
jasmine, lavender, chamomile, thyme, and lemon.
2.3. Cytotoxic activity towards cancer cells
To investigate the cytotoxic activities, three human tumor cell lines, A-549, PC- 3 and MCF-7,
were exposed to increasing concentrations of essential oils. Cell viability was determined by the MTT
assay. As shown in Figure 3 and Table 2 the essential oils revealed different cytotoxic activities
towards the three human cancer cell lines investigated. In general, a dose-dependent decrease in the
survival of the three tumor cell lines was observed. However, mint essential oil exhibited no effect on
A549 cell over a concentration range of 0.002% to 0.2% (v/v).
At a concentration of 0.002% (v/v), the essential oils did not considerably affect the viability of the
three human tumor cell lines compared with untreated control cells. The cell survival after treatment
with essential oils was more than 80%.
At a concentration of 0.200% (v/v), however, all essential oils exhibited strong cytotoxicities
towards PC-3 cells. Cell viability was lower than 4%. Most essential oils exhibited strong
cytotoxicities towards A549 cells. However, cells treated with mint essential oil still grew well, and
the number of survival cells was comparable to that of untreated control cells. For MCF-7 cell, the
cytotoxictiies of cinnamon, thyme, chamomile, and jasmine essential oils was significantly stronger
than that of the other six essential oils. The fractions of viable cells were reduced to 5.31%, 3.47%,
6.93% and 4.34%, respectively. Essential oils from grapefruit and ginger exhibited the lowest
Molecules 2010, 15
cytotoxicities towards MCF-7 cells. The percentages of cells viability were 75.03% and
Of all essential oils investigated, thyme essential oil exhibited the strongest cytotoxicities towards
cancer cells. The IC50 values for thyme essential oil against PC-3, A549 and MCF-7 cells were
0.010%, 0.011% and 0.030% (v/v), respectively. Moreover, cinnamon and jasmine essential oils
possessed stronger cytotoxic activities towards PC-3 and A549 cell lines. IC50 values for cinnamon
essential oil against PC-3 and A549 cells were 0.012% (v/v) and 0.017% (v/v). The IC50 values for
jasmine essential oil against these two cell lines were 0.022% (v/v) and 0.012% (v/v) respectively.
However, the IC50 values for cinnamon and jasmine essential oils against MCF-7 cells were 0.076%
(v/v) and 0.077% (v/v). MCF-7 cell was less sensitive than the other cell lines towards the essential oils.
Figure 3. Dose-dependent cytotoxicity of 10 essential oils (72 h exposure) towards PC-3
(A), A549 (B) and MCF-7 (C) cell lines as determined by the MTT assay. Values are
expressed as means ± SD of three independent experiments. Standard deviations were less
Table 2. Inhibition concentrations 50% (IC50, %v/v) values for 10 essential oils of PC-3,
A549 and MCF-7 cancer cell lines as determined by the MTT assay.
thyme chamomile lavender jasmine
grapefruit lemon ginger
Anti-bacterial and cytotoxic activities of essential oils can be attributed to their different
constituents. Essential oils comprise complex mixtures, including monoterpenes and sesquiterpenes,
such as limonene, menthol, α-pinene, 3-carene, and α-farnesol, etc. Some compositions have been
reported for their anti-bacterial activities towards bacteria and fungi [21,22]. The anti-cancer activities
of some monoterpenes and sesquiterpenes was also reported in the literature [23,24].
Until now, various authors have reported antitumor activities of essential oils as well as their
components. For instance, the lavender essential oil was found to be active against COL-2 , the
aldehyde compounds of Citrus paradisi essential oil induced apoptosis strongly in HL-60 cells ,
and thyme essential oil, which contains carvacrol, as the major component has an important in vitro
cytotoxic activity against tumor cells . In our results, ten essential oils (except for grapefruit,
Molecules 2010, 15
ginger and mint) also showed excellent antitumor activities against PC-3, A549, MCF-7. However,
further studies are urgently needed for screening for the mechanism of the antitumor activity.
3.1. Essential oils
Essential oils of mint (Mentha spicata), ginger (Zingiber officinale), lemon (Citrus limonum),
grapefruit (Citrus paradisi), jasmine (Jasminum grandiflora), lavender (Lavandula stoechas),
chamomile (Anthemis nobilis), thyme (Thymus vulgaris), rose (Rosa centifolia) and cinnamon
(Cinnamomum zeylanicum) were obtained from a commercial source (Xiamen Denyla Essential Ooil
Co., Ltd., Xiamen, China).
3.2. Maintenance of Proprionibacterium acnes
P. acnes (CMCC 65002) was purchased from China General Microbiological Culture Collection
Center (CGMCC, Beijing, China). The organism was incubated in brain heart infusion medium (BHI)
with 1% glucose (Aoboxing Biotech Company Ltd., Bejing, China) at 37 °C for 72 h under anaerobic
conditions and adjusted concentration by direct microscopic counts before the assay.
3.3. Disc diffusion assay
The determination of inhibition diameters of P. acnes colonies by essential oils was carried out by
the agar disc diffusion method . The BHI agar media plate was swabbed with the bacterial
suspension (108 CFU/mL) and kept for 30 min at 4 °C. Filter paper discs (6.0 mm in diameter) were
soaked with 5 µL essential oil and placed on the surface of the inoculated BHI agar plates. Plates were
incubated under anaerobic condition at 37 °C for 24 h. Three independent experiments were
performed, and the diameters were recorded as mean values.
3.4. Determinition of MICs and MBCs values
The MIC (minimal inhibitory concentration) and MBC (minimal bactericidal concentration) tests
were performed by the broth microdilution method . The essential oils were dissolved in sterilized
physiological saline solution (0.9%) supplemented with Tween-80 (Sigma) at final concentration of
0.5% (v/v). Serial two-fold dilutions from 1.000%–0.008% (v/v) of the essential oils were prepared
and placed into a 96-well micro-titer plate. One hundred µL of sample of each concentration were
dispensed into the wells of a micro-titer plate. Each well was then inoculated with 100 µL of the
bacterial suspension. The final concentration of the suspension was adjusted to 105 CFU/mL, and the
plate was incubated under anaerobic condition at 37 °C for 24 h. After incubation, the wells were
examined for growth of microorganisms and the MIC was determined. The MIC is defined as the
lowest concentration of the essential oil at which the bacterium does not demonstrate visible growth.
MBC was confirmed by reinoculating on agar plates with 10 µL of each culture medium from the
microplates. The number of CFU/mL was determined after 24 h of incubation at 37 °C. MBC is
Molecules 2010, 15
defined as the lowest concentration of the essential oil at which incubated microorganisms are
completely killed. Each experiment was repeated three times.
3.5. Time-kill dynamic curves
Time-kill dynamic procedures were performed as described by Avila et al.  with minor
modifications. The final concentration of suspension of the strain was adjusted to 105–106 CFU/mL.
According to the results of MIC and MBC of 10 essential oils, the 0.25% (v/v) concentration of each
essential oil was selected for use in the time-kill dynamic procedure. After incubating for 0, 5, 10, 20,
30, 45, 60, 90 and 120 min. with the broth micro dilution method, liquids (50 µL) were removed from
the test solution for ten-fold serial dilution. Thereafter, a 25 µL liquid from each dilution was spread
on the surface of the BHI agar plates and incubated at 37 °C under anaerobic condition for 24 h, and
the number of CFU/mL was counted. The solution with no essential oil was used as a control.
Experiments were carried out in triplicate. Time-kill curves were constructed by plotting the number of
CFU/mL against time (min).
3.6. Maintenance of human cancer cell lines
Human lung carcinoma (A549), human prostate carcinoma (PC-3) and human breast cancer cell
lines (MCF-7) were purchased from China Center for Type Culture Collection (Wuhan, China). These
cell lines were grown and maintained in a humidified incubator at 37°C with a 5% CO2 atmosphere.
Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS),
100 U/mL penicillin and 100 µg/mL streptomycin was used for the A549 cell cultures. Roswell Park
Memorial Institute Medium (RPMI) 1640 medium supplemented with 10% FBS, 100 U/mL penicillin
and 100 µg/mL streptomycin was used as the culture medium for PC-3 and MCF-7 cells.
3.7. Cytotoxicity assay
The cytotoxic effects of the essential oils on three human tumor cell lines were assayed by the
MTT assay . The cells were seeded at a density of 5 × 104 cells/well. The 10 essential oils were
serially double diluted from 0.200% to 0.002% (v/v), and 100 μl liquid of each concentration was applied
to the wells of a 96-well plate containing confluent cell monolayers (six wells per concentration). The
dilution medium without the sample served as a control. After 72 h of incubation, MTT solution
(5 mg/mL) was then added to each well. and the formazan precipitate was dissolved in 100 μL
dimethyl sulfoxide after 4 h incubation, After shaking for 5 min, the content of the wells was
homogenized on a microplate shaker. The optical densities (OD) were measured on a microplate
ELISA reader at 570 nm. All tests and analyses were run in triplicate and mean values were recorded.
The cell survival curves were calculated after comparing with the control. The percentage viability was
calculated as follows:
oil) (no wells control of absorbance mean
wells treatedof absorbance mean
Molecules 2010, 15
Among the 10 essential oils investigated in the present study, thyme and cinnamon essential oils
exhibited the strongest anti-bacterial activities towards P. acnes and cytotoxic activities towards A549,
PC-3, and MCF-7 human tumor cell lines. The main components of thyme essential oil is thymol ,
whose anti-microbial activities have been previously reported . Its mechanism of action towards S.
aureus and E. coli was also reported . The main component of cinnamon is eugenol , which
possesses notable anti-bacterial and anti-oxidant effects . It was also found to be a potent inhibitor
of melanoma cell proliferation . We hypothesize that these two constituents may also be
responsible for the antibacterial and cytotoxic activities of thyme or cinnamon essential oil observed in
this investigation. Other essential oils also comprise monoterpenes, such as limonene and menthol, that
possess bioactivity. On the basis of our results, 10 ten essential oils analyzed in this study may be used as
alternative for food, cosmetics and medicine. In addition to their use for food and cosmetics, the
potential of essential oils for the treatment of acne and cancer merits further exploration in the future.
The authors gratefully acknowledge the financial supports by National Natural Science Foundation
of China (30770231), Heilongjiang Province Science Foundation for Excellent Youths (JC200704),
Agricultural Science and Technology Achievements
(2009GB23600514), Key Project of Chinese Ministry of Education (108049), National Key
Technology R & D Program (2006BAD18B0405), Innovative Program for Importation of
International Advanced Agricultural Science and Technology, National Forestry Bureau (2006-4-75),
Key Program for Science and Technology Development of Harbin (2009AA3BS083), Research
Foundation for Science, Technology Innovation Talents of Harbin (2006RFXXS001) and Fundamental
Research Funds for the Central Universities (DL09EA04).
Transformation Fund Program
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