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, 18 (1), 143

Use of Pinus Sylvestris L. (Pinaceae), Origanum Vulgare L. (Lamiaceae), and Thymus Vulgaris L. (Lamiaceae) Essential Oils and Their Main Components to Enhance Itraconazole Activity Against Azole Susceptible/Not-Susceptible Cryptococcus Neoformans Strains

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Use of Pinus Sylvestris L. (Pinaceae), Origanum Vulgare L. (Lamiaceae), and Thymus Vulgaris L. (Lamiaceae) Essential Oils and Their Main Components to Enhance Itraconazole Activity Against Azole Susceptible/Not-Susceptible Cryptococcus Neoformans Strains

Daniela Scalas et al. BMC Complement Altern Med.

Abstract

Background: Cryptococcal infections, besides being a problem for immunocompromised patients, are occasionally being a problem for immunocompetent patients. In addition, the lower susceptibility of this yeast to azoles is a growing problem in health care. To date, there are very few molecules with any activity towards Cryptococcus neoformans, leading to heightened interest in finding new alternatives or adjuvants to conventional drugs for the treatment of mycosis caused by this yeast. Since the essential oils (EOs) are considered as a potential rich source of bioactive antimicrobial compounds, we evaluated the antifungal activity of Origanum vulgare (oregano), Pinus sylvestris (pine), and Thymus vulgaris (thyme red) EOs, and their components (α-pinene, carvacrol, thymol) compared with fluconazole, itraconazole, and voriconazole, against C.neoformans clinical strains. Then, we investigated the effect of EOs and components in combination with itraconazole.

Methods: EO composition was analysed by Gas chromatography-mass spectrometry (GC-MS). A broth microdilution method was used to evaluate the susceptibility of C.neoformans to azoles, EOs and components. Checkerboard tests, isobolograms and time-kill assays were carried out for combination studies.

Results: Six C.neoformans isolates were susceptible to azoles, while one C.neoformans exhibited a reduced susceptibility to all tested azole drugs. All EOs exerted a good inhibitory activity against all C.neoformans strains. Pine EO was the most effective. Among components, thymol exerted the most remarkable activity. By checkerboard testing and isobolographic analysis, combinations of itraconazole with oregano, pine, or thyme EOs, and carvacrol were found to be synergistic (FICI≤0.5) against azole susceptible C.neoformans. Regarding the azole not susceptible C.neoformans strain, the synergistic effect with itraconazole was observed with thyme EO (chemotype: thymol 26.52%; carvacrol 7.85%), and carvacrol. Time-kill assays confirmed the synergistic effects of itraconazole and oregano or thyme EO against azole susceptible C.neoformans. Binary mixtures of itraconazole/thyme EO or carvacrol yielded additive effects on the azole not susceptible C.neoformans.

Conclusions: Our findings highlight the potential effectiveness of thyme, oregano EOs, and carvacrol as natural and cost-effective adjuvants when used in combination with itraconazole. Identification of EOs exerting these effects could be one of the feasible ways to overcome drug resistance, reducing drug concentration and side effects.

Keywords: Antifungal activity; Combinatorial interaction; Cryptococcus neoformans; Essential oils; Itraconazole.

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Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
Isobologram plots of ITC and EOs/EO main components against C.neoformans ADS 37 (azole-susceptible strain). Points along the isobolograms represent the growth no-growth interface: fractional inhibitory concentration (FIC) values of ITC are plotted on x-axis, and FIC values of EOs/EO main components are plotted on y-axis
Fig. 2
Fig. 2
Isobologram plots of ITC and EOs/EO main components against C.neoformans ADS 006 (azole not-susceptible strain). Points along the isobolograms represent the growth no-growth interface: fractional inhibitory concentration (FIC) values of ITC are plotted on x-axis, and FIC values of EOs/EO main components are plotted on y-axis
Fig. 3
Fig. 3
Time-kill curve of ITC, oregano and thyme red EOs alone and in combination against C.neoformans ADS 37 (azole-susceptible strain)
Fig. 4
Fig. 4
Time-kill curve of ITC, pine EO and carvacrol alone and in combination against C.neoformans ADS 37 (azole-susceptible strain)
Fig. 5
Fig. 5
Time-kill curve of ITC, thyme red EO and carvacrol alone and in combination against C.neoformans ADS 006 (azole not-susceptible strain)

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References

    1. Gullo FP, Rossi SA, Sardi Jde C, Teodoro VL, Mendes-Giannini MJ, Fusco-Almeida AM. Cryptococcosis: epidemiology, fungal resistance, and new alternatives for treatment. Eur J Clin Microbiol Infect Dis. 2013;32:1377–1391. doi: 10.1007/s10096-013-1915-8. - DOI - PubMed
    1. Mandras N, Roana J, Tullio V, Allizond V, Banche G, Scalas D, Fucale G, Cuffini AM. A case of fluconazole, voriconazole-resistant Cryptococcus neoformans isolated from an immunocompetent patient. J Chemother. 2011;23:379–380. doi: 10.1179/joc.2011.23.6.379. - DOI - PubMed
    1. Elkin I, Rabanel JM, Hildgen P. Influence of hydrophobic dendrimer core structure on the itraconazole encapsulation efficiency. Macromol Chem Phys. 2015;216:2356–2367. doi: 10.1002/macp.201500211. - DOI
    1. Mandras N, Roana J, Scalas D, Fucale G, Allizond V, Banche G, Barbui A, Li Vigni N, Newell VA, Cuffini AM, Tullio V. In vitro antifungal activity of fluconazole and voriconazole against non-Candida yeasts and yeast-like fungi clinical isolates. New Microbiol. 2015;38:583–587. - PubMed
    1. Cannas S, Usai D, Tardugno R, Benvenuti S, Pellati F, Zanetti S, Molicotti P. Chemical composition, cytotoxicity, antimicrobial and antifungal activity of several essential oils. Nat Prod Res. 2016;30:332–339. doi: 10.1080/14786419.2015.1060592. - DOI - PubMed

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