Molecular and Cellular Biochemistry 228: 111–117, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.

111

Antifungal activities of origanum oil against
Candida albicans
Vijaya Manohar,1 Cass Ingram,2 Judy Gray,2 Nadeem A. Talpur,1 Bobby
W. Echard,1 Debasis Bagchi3 and Harry G. Preuss1
1

Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC; 2North American
Herbs and Spices, Waukeegan, IL; 3Department of Pharmacy Sciences, Creighton University School of Pharmacy and AHP,
Omaha, NE, USA
Received 27 June 2001; accepted 14 September 2001

Abstract
The antimicrobial properties of volatile aromatic oils from medicinal as well as other edible plants has been recognized since
antiquity. Origanum oil, which is used as a food flavoring agent, possesses a broad spectrum of in vitro antimicrobial activities
attributed to the high content of phenolic derivatives such as carvacrol and thymol. In the present study, antifungal propertiesof origanum oil were examined both in vitro and in vivo. Using Candida albicans in broth cultures and a micro dilution method,comparative efficacy of origanum oil, carvacrol, nystatin and amphotericin B were examined in vitro. Origanum oil at 0.25
mg/ml was found to completely inhibit the growth of C. albicans in culture. Growth inhibitions of 75% and >50% were observed at 0.125 mg/ml and 0.0625 mg/ml level, respectively. In addition, both the germination and the mycelial growth of C.
albicans were found to be inhibited by origanum oil and carvacrol in a dose-dependent manner. Furthermore, the therapeutic
efficacy of origanum oil was examined in an experimental murine systemic candidiasis model. Groups of mice (n = 6) infectedwith C. albicans (5 × LD50) were fed varying amounts of origanum oil in a final vol. of 0.1 ml of olive oil (vehicle). The dailyadministration of 8.6 mg of origanum oil in 100 µl of olive oil/kg body weight for 30 days resulted in 80% survivability, withno renal burden of C. albicans as opposed to the group of mice fed olive oil alone, who died within 10 days. Similar results
were obtained with carvacrol. However, mice fed origanum oil exhibited cosmetically better clinical appearance compared tothose cured with carvacrol. The results from our study encourage examination of the efficacy of origanum oil in other formsof systemic and superficial fungal infections and exploration of its broad spectrum effect against other pathogenic manifestations including malignancy. (Mol Cell Biochem 228: 111–117, 2001
Key words: antifungal activity, in vitro, in vivo, female BALB/c mice, origanum oil, Candida albicans, carvacrol, nystatin,
amphotericin B

Introduction
The antimicrobial properties of volatile aromatic oils fromedible plants have been recognized since antiquity. Origanum oil, which is used as a food flavoring agent, has beenshown to possess a broad spectrum of antimicrobial activity due to its high content of phenolic derivatives such as
carvacrol and thymol [1–3]. Earlier studies have demonstrated the ability of origanum oil to retard and inhibit thegrowth of various food spoiling organisms including thespecies of Aspergillus (mycotoxinogenic filamentous fungi)and Hansenula (industrial yeasts) [4–7]. While the oil andmany of its constituents have been demonstrated to be antifungal in vitro against non-pathogenic yeasts [8, 9], a few
studies have suggested a potential therapeutic effect against
experimental infections in rats due to Trichophyton rubrum,
a human dermatophytic filamentous fungus) [10]. Nevertheless, very little information is available on its compara-

Address for offprints: H.G. Preuss, Department of Physiology and Biophysics, Georgetown University Medical Center, Med-Dent Building, SE103, 3900
Reservoir Road, NW, Washington, DC 20007, USA (E-mail: preusshg@georgetown.edu)

112tive antifungal activity on the growth and physiology ofhuman pathogenic yeasts or filamentous fungi either in vitro
or in vivo. Furthermore, its direct therapeutic use either insuperficial or systemic infections due to bacteria or fungi has
not been clearly established. In the present study, we examined the antifungal properties of origanum oil and its major
chemical constituent carvacrol against Candida albicans, a dimorphic yeast-like fungus. C. albicans which resides as commensal in the mucocutaneous cavities of skin, vagina andintestine of humans [11], can cause infections under alteredphysiological and pathological conditions such as infancy,
pregnancy, diabetes, prolonged broad spectrum antibiotic administration, steroidal chemotherapy as well as AIDS [12–18]. We have demonstrated that origanum oil inhibits thegrowth of C. albicans in vitro as well as in vivo. We conclude
that the daily oral administration of origanum oil may be highly
effective in the prevention and treatment of candidiasis.

Materials and methods
Animals and treatment
Female BALB/c mice (15–18 g) were obtained from Taconic
Farms (Germantown, NY, USA). The animals were maintained in a controlled environment at 25°C with a 12 h lightand 12 h dark cycle, and were acclimatized for 3–5 days
before use. The mice were housed in groups of five, fed commercial rodent pellets and given water ad libitum throughout the experiments. The protocol for the entire investigation
was approved by the Animal Welfare Board at Georgetown
University Medical Center.

Susceptibility testing
A micro-broth dilution technique was employed to determine
the susceptibility of the strains of C. albicans to oil of origanum and carvacrol [19, 20]. Susceptibility was expressed asminimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC). The stock solutions of origanum oil, olive oil and carvacrol (63% v/v adjusted in oliveoil) were dissolved in ethanol-Tween 80 solvent. Nystatin andamphotericin B were dissolved in 50% ethanol, and used as
positive controls. Solvent and media controls were also included for reference. The Sabouraud’s glucose (S.g) brothcontaining varying amounts (logarithmic, serially and 2-folddiluted) of origanum oil and carvacrol and the various controls were inoculated with actively dividing C. albicans cells.
The cultures were incubated for 24 and 48 h at 30°C on ametabolic rotary shaker (200 rev/min), and the growth wasmonitored both visually and colorimetrically (at 540 nM).
The minimum inhibitory concentration (MIC) was definedas the lowest concentration required to arrest the growth of
the fungi at the end of 24 h of incubation. Minimum fungicidal concentration (MFC) was determined by sub-culturinga 0.01 ml aliquot of the medium drawn from the culture tubes
showing no macroscopic growth at the end of 48 h of culture on S.g. agar plates and incubated further for the appearance of yeast-like growth. The plates were scored for growthof the yeast colonies. The lowest concentration of the antifungal agent from which negative growth or fewer than 3colonies were recorded was considered as minimum fungicidal concentration (MFC).

Effect on yeast and mycelial forms of C. albicans

Origanum (P73 OreganolTM) and olive oil were provided by
North American Herbs and Spices, Waukegan, IL, USA. Carvacrol, nystatin and amphotericin B were purchased from
Sigma Chemical Co. (St. Louis, MO, USA). Sabouraud’s glucose (S.g) broth and agar media were purchased from Difco
Laboratories (Detroit, MI, USA). All other chemicals usedin this study were obtained from Sigma Chemical Co. (StLouis, MO, USA) and were of analytical grade or the highest commercial grade available.

The effect of origanum oil on the formation of germ tubes(filament initiation) by C. albicans was examined, by incubating the blastospores with various concentrations of origanum oil, carvacrol and other agents in 20% egg albumin at
37°C [21]. The comparative percentage inhibition of germtube formation was determined by microscopic examination.
The effect on the mycelial formation (filament elongation) was
carried out by incubating the previously germinated blastospores of C. albicans in the presence of varying amounts of
antifungal agents at 37°C for an additional 24 h and 48 h. Boththe germination and the filament elongation were microscopically monitored. The MIC and MFC were determined as above.

Organisms

Toxicity tests with miceStandard strain of Candida albicans (ATCC No. 48274) obtained from ATCC, Fairfax, VA, USA, was grown and maintained on S.g. agar slants.

Since origanum oil is known to be pungent and corrosive, atitration of the doses of origanum oil was conducted to determine the tolerable dose to be given orally. Both the neat

Plant oils and chemicals

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oil and the dilutions in olive oil (vehicle) were orally administered to the mice according to the body weight using a ball
tip gavage needle (Harvard Apparatus, South Natick, MA,
USA). Higher concentrations of the oil were given as single
bolus dose, while the lower concentrations were given dailyfor 7 days. The overall health of the animals such as coatcolor, body weight, other side effects such as scruffiness, anddeath were recorded for 14 days. At the end of the experiment, mice were sacrificed to visually examine the internalorgans for any abnormalities.

Effect on experimental murine systemic candidiasis
A murine systemic candidiasis model developed previously[22], was employed to evaluate the in vivo anti fungal activities of origanum oil and carvacrol. Initially, the concentrations of C. albicans needed to achieve 50% mortality of theanimals (LD50) were determined. Mice were injected i.v. withvarying doses of actively growing C. albicans in a final vol.
of 0.1 ml. Mortality of mice was monitored for 30 days. The
death of the mice due to C. albicans was confirmed by anatomical evidence for organ involvement, i.e. the histologicalpresence of yeasts and/or pseudomycelia. Furthermore, renal burden of C. albicans was assessed by culturing an aliquot of the kidney homogenate on S.g. agar plates. The dose
titration revealed that 2.5 × 106 C. albicans cells were needed
to kill 50% of the mice. Subsequently, batches of mice injected with 5 × LD50 dose of C. albicans were used to assesstherapeutic activity.

Treatment protocol
In two separate experiments, groups of mice (6 each) infected with C. albicans (5 × LD50) were gavaged, daily withoriganum oil or carvacrol in 0.1 ml of olive oil for 8 daysand 30 days. The amount of antifungal agents administered
was calculated based on the body weight of the mice. Control mice received either olive oil orally alone (negative
control), or olive oil orally plus amphotericin B 25 µg i.p.
(positive control). The experiments were terminated at theend of 30 days. The body weights, the disease status andthe overall health of the mice during the experiment wererecorded. The pathological status of the mice was determined by visual examination of the internal organs after
their death or sacrifice at the completion of the experiment.
For histology, kidney smears were examined microscopically after staining with 1% methylene blue for the presenceof fungal elements. Renal burden of C. albicans was further tested by culturing aliquots of kidney homogenates on
S.g. agar plates.

Results
Origanum oil is fungicidal to C. albicans in vitro
In the present study, we have examined the antifungal properties of origanum oil and one of its major constituents, carvacrol and thymol, both in vitro and in vivo. Using Candida
albicans in broth cultures and a micro-dilution method, comparative efficacies of origanum oil, carvacrol, nystatin andamphotericin B were examined in vitro. Origanum oil at 0.25
mg/ml was found to completely inhibit the growth of C. albicans in culture. Growth inhibitions of 75% and >50% wereobserved at 0.125 mg/ml and 0.0625 mg/ml level, respectively (Table 1). Figure 1 provides a pictorial presentation of
the inhibitory effect. A 2-fold higher concentration of carvacrol was required to be fungicidal.

Both the germination and mycelial elongation of C.
albicans are inhibited in vitro
Origanum oil and carvacrol both inhibit germ-tube formationby the blastospores of C. albicans (Table 2). The productionof germ tubes and subsequent mycelial formation when exposed to either serum or hen’s egg albumen is an in vitro
correlate of the in vivo tissue invasive capabilities of thepathogenic strains of C. albicans. Origanum oil inhibited
Table1. Effect of origanum oil on the growth of Candida albicans
Agent

24 h MIC(mg/ml)48 h MFC(mg/ml)Origanum oil
Carvacrol
Amphotericin B
Nystatin
Olive oil

0.125
0.25
0. 0015
0. 005
No effect

0.25
0.5
0.00150.005
No effect

MIC = minimum inhibitory concentration; MFC = minimum fungicidal
concentration.

Table 2. Effect of origanum oil on germ tube formation and filament elongation
Agent

Origanum oil
Carvacrol
Olive oilGerm tube formation

Filament elongation

MIC
mg/ml

MFC
mg/ml

MIC
mg/ml

MFC
mg/ml

0. 062
0. 125
NE

0.125
0.125
NE

0.125
0.125
NE

0.125
0.25
NE

NE = no effect; MIC and MFC for nystatin and amphotericin B = 2.5 and5.0 µg/ml respectively.

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Fig. 1. In vitro antifungal activity of origanum oil against Candida albicans. Exponentially growing C. albicans cells were cultured with varying concentrations of antifungal agents. Aliquots from the cultures drawn at the end of 48 h of culturing were plated on to Sabouraud’s glucose agar. The plates were
further incubated for an additional 48 h for the appearance of yeast like colonies.

germ-tube production by blastospores of C. albicans in a dosedependent manner. The MIC required to inhibit the productionof germ tube formation was 0.062 mg/ml (24 h) and the fungicidal effect (at 48 h) required double the concentration(MFC = 0.125 mg/ml). Carvacrol exerted effects similar tooriganum oil at twice the concentrations. Origanum oil andcarvacrol were also found to affect filament elongation. The
mycelial forms of C. albicans were also inhibited by origanum oil at 0.125 mg/ml (MIC) and 0.125 mg/ml (MFC) levels, and by carvacrol at 0.125 mg/ml (MIC) and 0.25 mg/ml(MFC) levels, respectively.

Table 3. Toxicity of origanum oil to BALB/c mice

Origanum oil can protect mice from systemic candidiasis*Oil was mixed with 100 µl olive oil and gavaged.

The therapeutic efficacy of origanum oil was examined in anexperimental murine systemic candidiasis model. Toxicity
studies to determine the least toxic dose of origanum oil thatcan be fed safely to mice were conducted (Table 3). A single
bolus dose of 650 mg/kg body weight caused uniform mortality. However, daily administration of smaller doses of origanum oil mixed with olive oil was well tolerated, showing
no apparent clinical abnormalities (Table 3).
In the first in vivo study, the therapeutic ability of origanum oil given only for 8 days to prevent the mortality of micewith systemic infection due to C. albicans was tested (Table
4). Groups of mice (n = 6) infected with C. albicans (5 × LD50)
were gavaged with varying amounts of origanum oil in a final vol. of 0.1 ml. An 8-day treatment with 162.5 mg and 325

Concentration of oil*
(mg/kg)No. of mice
(tested/survived)

Bolus dose

2600
1300
650
325.0
162.5

5/0
5/0
5/0
5/5
5/5

Daily dose for 1 week

26
52
78
104
130

6/6
6/6
6/6
6/6
6/6

Table 4. Therapeutic efficacy of origanum oil: 8-day treatment
Agent

Conc. @ per
No. of mice
No. of mice withkg body wt. (mg) tested/survived renal burden#

Origanum oil

325. 5162. 5
1. 0

Amphotericin B
Olive oil (vehicle)

6/6
6/6
6/6
6/0*

4/6
6/6
2/6
–

*Died within 10 days. #Renal burden+ = kidney smear+ culture+.

mg per kg body weight was found to rescue the mice frommortality with 100% survival rate over the 30 days of observation, similar to mice that received amphotericin B (1 mg/

115
Table 5. Therapeutic efficacy of origanum oil: 30-day treatment
Agent

Conc. @ per
No. of mice
kg body wt. (mg) tested/survived

Origanum oil

52. 0043. 3331. 0026. 0017. 33
8. 66
Carvacrol
17. 33
8. 66
Amphotericin B 1. 0
Olive oil

6/6
6/6
6/6
6/6
6/6
6/5
6/6
6/5
6/6
6/0*

No. of mice withrenal burden#
0/6
0/6
0/6
0/6
0/6
0/5
0/6
0/5
0/6
6/6

*Died within 10 days. #Renal burden+ = kidney smear+ culture+. One mouse
treated with 8.66 mg origanum oil/kg b.w. died on day 15, while one mouse
treated with 8.66 mg carvacrol/kg b.w. died on day 13.

kg body weight). In contrast, the control group of mice who
received 0.1 ml of olive oil alone died within 10 days. At theend of 30 days, the surviving animals appeared to be clinically
healthy, without scruffiness and with regain of normal coatluster. Internally, no abnormalities of organs were noted. Furthermore, the kidney smears failed to demonstrate the presence of either yeasts or pseudomycelia. However, the cultureof their kidney homogenates on S.g. agar revealed the presence of C. albicans. (Table 4).
The results from the second experiment to determine theoptimal dose over a 30-day treatment course required forclinical cure and to completely eliminate the renal burden of
C. albicans are shown in Table 5. A daily administration oforiganum oil as low as 8.66 mg/kg body weight (equivalentof 1 µl per mouse) was found to cure 80% of the infected
mice. Initially all groups of infected mice, exhibited scruffiness, loss of body weight, and lack of coat luster. In the vehicle-control mice, the average body weight was found to
decrease 7 days after injection from approximately 16–11 g.
In contrast, mice receiving treatment had a gradual increasein body weight after injection from 15–17 to 16–19 g by theend of 30 days (Fig. 2). The daily administration of equivalent amounts (8.66 and 17.33 mg/kg body weight) of carvacrol was found to confer similar therapeutic properties (datanot shown). However, the overall clinical appearance of themice receiving origanum oil was cosmetically better thanthose receiving carvacrol, as evidenced by the improved coatluster and minimal scruffiness.

Discussion
Aromatic herbal oils used for cooking and flavoring are increasingly claimed to have broad spectrum antimicrobialactivities. Origanum oil has been suggested to have potent

Fig. 2. In vivo effect of origanum oil in experimental murine candidiasis.
Infected mice were fed orally with varying amounts of origanum oil in 0.1
ml vol. of olive oil (vehicle). The control animals received either olive oilalone or olive oil plus amphotericin B (i.p.). The body weights and theoverall health of the mice were recorded daily.

antimicrobial activity, including anthelmintic properties, due
to its phenolic, alcoholic and terpenoid constituents [4]. The
objective of the present study was to assess the antifungal
properties of origanum oil against C. albicans in both in vitro
and in vivo. Furthermore, the comparative efficacy of origanum oil, carvacrol, nystatin and amphotericin B was also
examined. The results clearly demonstrate that the origanum
oil can act as a potent antifungal agent against C. albicans,and can function similar to antifungal antibiotics such as
nystatin or amphotericin B.
C . albicans is a harmless commensal yeast-like fungus in
healthy humans, which can cause superficial as well as lifethreatening systemic infections under immune compromised
situations. C .albicans can colonize or infect virtually all bodysites because of its high adaptability to different host niches
by the activation of appropriate sets of genes in response tocomplex environmental signals [21–25]. Thus, our objective was to assess the possible therapeutic potential of thecommonly used origanum oil against this human dimorphic
commensal, which can become a facultative pathogen under altered physiological situations.
Previous studies to assess the inhibitory effect of origanum
oil against twenty-five different genera of microorganisms
including animal and plant pathogens, food poisoning andspoilage bacteria, have demonstrated the growth inhibition
properties by origanum oil [26]. Essential oils of oregano(Origanum vulgare) were found to inhibit the growth andproduction of ochratoxin A by Aspergillus ochraceus NRRL
3174 up to 21 days in culture [27].
Origanum oil has been shown to delay or inhibit the growthof saprophytic food spoiling fungi such as Aspergillus flavus (mycotoxogenic) and industrial yeasts such as Hansenula

116
anoma [8]. Furthermore, origanum oil, and carvacrol havebeen reported to have some promising effect on rats infectedwith a human dermatophytic fungus, Trichophyton rubrum[10]. However, the essential oils including origanum oil at
100 ppm had no effect on the pseudomycelial formation by
Candida lipolytica [10,11].
In this paper we have demonstrated, that origanum oil effectively inhibits the in vitro growth of C. albicans, a humanyeast-like fungus which can cause both systemic and superficial infections in debilitated individuals. In addition we haveshown that origanum oil directly inhibits germination andfilament formation (the two phases required for tissue invasion) by C. albicans. Nevertheless, the novel fungicidal property of origanum oil was of superior efficacy as compared tocarvacrol against the germination and mycelial elongation ofpathogenic strain of C. albicans in vitro. Furthermore, selectedconcentrations of origanum oil demonstrated therapeutic efficacy comparable to the effective examined dose for amphotericin B (1.0 mg) in protecting the mice from systemic
candidiasis. The overall clinical appearance of the mice receiving origanum oil was cosmetically better than those receiving carvacrol (data not shown), although this difference
in appearance could possibly be attributed to the presence ofadditional constituent phenols such as thymol, terpenes andflavonoids in origanum oil [4]. It has been demonstrated thatsome of these components of origanum oil have antispasmodic and antioxidant activities, in addition to their antimicrobial potentials [23, 28, 29]. A comparative study of thesecomponents may shed more light not only on the antifungal
potentials, but also on the pharmacological effects of each ofthese components. It is interesting to speculate that secondary
infections due to C. albicans in debilitated individuals such as
those having diabetes and HIV infection may be prophylactically controlled by the daily intake of small amounts oforegano oil, either alone or added to a food.
In summary, the results presented in this paper conclusively
demonstrate the antifungal potential of edible origanum oil.
Origanum oil is shown to be both fungistatic and fungicidal
to C. albicans, the human pathogenic yeast. Both the germination and the pseudomycelial phase of the yeast are inhibited in vitro. Further, the daily oral administration of as little
1.0 µl of oil for 30 days completely freed 80% of the laboratory mice from experimental systemic candidiasis, which isfatal if not treated. Thus, daily oral administration of origanum
oil may be highly effective in the prevention and treatment ofcandidiasis. The results from our study not only encourage
examination of the efficacy of origanum oil in other formsof systemic and superficial fungal infections, but also to explore its broad spectrum effect against other pathogenic
manifestations including malignancies.

Acknowledgement
This work was supported by a generous grant from North
American Herb and Spice located in Waukeegan, IL, USA.
Oreganum oil was a generous gift from the North American
Herb and Spice, Waukeegan, IL, USA.

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