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. 2018 Aug 28;23(9):2164.
doi: 10.3390/molecules23092164.

Origanum vulgare L. Essential Oil as a Potential Anti-Acne Topical Nanoemulsion-In Vitro and In Vivo Study

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Origanum vulgare L. Essential Oil as a Potential Anti-Acne Topical Nanoemulsion-In Vitro and In Vivo Study

Mohammed H Taleb et al. Molecules. .
Free PMC article

Abstract

Antibiotics are often prescribed in acne treatment; however, Propionibacterium acnes and Staphylococcus epidermidis, the two of the major acne-associated bacteria, developed antibiotic resistance. Essential oils (EOs) present a natural, safe, efficacious and multifunctional alternative treatment. This study aimed to assess the potential anti-acne activity of selected seven EOs commonly used in Mediterranean folk medicine. Antimicrobial activity screening of these oils showed oregano to exhibit the strongest antimicrobial activity with minimum inhibitory concentration (MIC) of 0.34 mg/mL and minimum bactericidal concentration (MBC) of 0.67 mg/mL against P. acnes; and MIC of 0.67 mg/mL and MBC of 1.34 mg/mL against S. epidermidis. The composition of the most effective EOs (oregano and thyme) was determined using gas chromatography-mass spectrometry (GC-MS). Monoterpenoid phenols predominated oregano and thyme EO with thymol percentile 99 and 72, respectively. Thymol showed MIC 0.70 mg/mL against both P. acnes and S. epidermidis whereas MBC was 1.40 and 2.80 mg/mL against P. acnes and S. epidermidis, respectively. Moreover, oregano exhibited the strongest anti-biofilm effect against S. epidermidis with MBIC 1.34 mg/mL and killing dynamic time of 12 and 8 h against P. acnes and S. epidermidis, respectively. Oregano, the most effective EO, was formulated and tested as a nanoemulsion in an acne animal mouse model. The formulation showed superior healing and antimicrobial effects compared to the reference antibiotic. Collectively, our data suggested that oregano oil nanoemulsion is a potential natural and effective alternative for treating acne and overcoming the emerging antibiotic resistance.

Keywords: P. acnes; S. epidermidis; acne vulgaris; antibiotic resistance; antimicrobial activity; essential oils; nanoemulsion; oregano; thymol.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Oregano EO exhibited the largest inhibition zone among the tested oils. Antibacterial activity of the screened EOs using agar disc diffusion method against (a) S. epidermidis with EOs at concentration of 0.7%; (b) S. epidermidis with EOs at concentration of 1.4%; (c) P. acnes with EOs at concentration of 0.7%; (d) P. acnes with EOs at concentration of 1.4%. Data is represented as means of inhibition zones (mm) ± SD. Controls used were clindamycin and erythromycin as positive control, while DMSO as negative control.
Figure 2
Figure 2
Oregano EO inhibited the growth of S. epidermidis faster than P. acnes. Oregano EO at concentrations of 0.672, 1.34, 2.68 mg/mL (1, 2, 4 MIC) and no EO control was used for assaying the killing rate of bacterial cells at 0, 2, 4, 8 and 12 h and expressed as the surviving bacteria (log10 CFU/mL) at different exposure times. We used starting bacterial suspension concentration 108 CFU/mL. Oregano EO killing rate against (a) S. epidermidis and (b) P. acnes.
Figure 3
Figure 3
Thymol exhibited lower inhibition zone than oregano EO. Antibacterial activity of thymol and the most bioactive EOs using disc diffusion method (zone of inhibition in mm) against (a) S. epidermidis with thymol and EOs at concentration of 0.7%; (b) S. epidermidis with thymol and EOs at concentration of 1.4%; (c) P. acnes with thymol and EOs at concentration of 0.7%; (d) P. acnes with thymol and EOs at concentration of 1.4%. Data is represented as means of inhibition zones (mm) ± SD. Controls used were clindamycin and erythromycin as positive control with DMSO as negative control.
Figure 4
Figure 4
Oregano EO nanoemulsion showed stronger inhibition of inflammation than erythromycin control in acne mouse model. The acne mouse model was induced by intradermal injection of BALB/c mice’s left ears with 108 CFU in 20 mL of P. acnes. The mice’s right ears served as uninfected control. We applied epicutanously either oregano EO nanoemulsion or 2% Erythromycin solution on the infected mice ears. A third group of mice served as untreated control. (a) Percent inflammation was assessed post epicutaneous application of treatment as the difference between each mouse ear thickness of infected and uninfected ears. Oregano nanoemulsion showed higher rate of reduction in inflammation than 2% erythromycin during the treatment time interval. (b) Oregano nanoemulsion showed significantly higher percent of inhibition of inflammation (>60%) at the end of treatment period than 2% erythromycin control (20%). Data represented as mean ± standard deviation of three independent experiments, total mice per group 15 mice. We used t-test for comparing groups with p < 0.05 consider significant.
Figure 5
Figure 5
Oregano nanoemulsion as a potent anti-acne agent tested in vivo model of P. acnes infection Photo images of BALB/c mice ear skin at the end of the experiment showing (a) untreated control mice, one ear injected with 20 μL of 108 CFU P. acnes suspension showing microcomedones and inflammation in infected left ear compared to the uninfected right ear; (b) inflammation in left infected ear disappeared after treatment with erythromycin solution comparable to the right uninfected ear; (c) absence of inflammatory appearance in left infected ear treated by oregano formula; (d) histopathological analysis of uninfected mice ear skin tissue stained with hematoxylin and eosin showing normal histology of mouse ear tissue with basal layer and epidermal cell maturation preserved; (e) histopathology of infected untreated control mice ear showing necrotic dermatitis character; note the severe dermal necrosis (arrow head), and lymphocytic infiltrate (arrow); (f) ear showing acute dermatitis character; note the congested blood vessels (arrow head), and slight lymphocytic cells infiltration (arrow) treated by erythromycin solution; (g) ear showing apparently normal histology of mouse ear tissue with the absence of inflammatory reaction, treated with oregano formula.
Figure 6
Figure 6
Oregano EO nanoemulsion showed higher antimicrobial effect against P. acnes than erythromycin control in acne mouse model. We induced acne in a mouse model by intradermal injection of BALB/c mice left ears with 108 CFU in 20 µL of P. acnes. The mice’s right ears served as uninfected control. We applied epicutanously either oregano EO nanoemulsion or 2% Erythromycin solution on infected mice ears. A third group of mice served as untreated control. Viable counts of P. acnes load in mice ears at the end of the treatment of various mice groups were performed. Oregano nanoemulsion significantly lowered bacterial load in treated mice ears than 2% Erythromycin. Bacterial load was expressed as Log10 CFU/mL. Data represented as mean ± standard deviation of three independent experiments, total mice per group 15 mice. T-test was used for comparing groups with p < 0.05 considered significant.

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