With the wide use of synthetic and semi-synthetic antimicrobial drugs, pros and cons have been so far experienced, including the spread of drug resistant pathogens, and have directed research back to natural products as useful antimicrobial resources. Currently, there is evidence that essential oils (EOs) may exert remarkable biological activities against viruses, bacteria, fungi and parasites. The antimicrobial activity of EOs is due to a number of small terpenoids and phenol compounds. Several EOs are generally recognized as safe, do not accumulate in the liver or kidneys, can stimulate the immune system, and cause no resistance, since microbes are unable to adapt to their heterogeneous structure. The promising antimicrobial activity of EOs has led researchers to use them in combination with available antimicrobial drugs, in order to reduce drug toxicity and side effects, as well as to overcome drug resistance with single agents. Mentha x piperita L. (peppermint) EO is one of the most widely produced and consumed essential oils. Literature data have shown that peppermint EO and its main components (menthol and menthone) display antimicrobial properties, but their mechanism of action is still not clear. Near Torino, in Pancalieri, there is a typical local production of M.piperita [(Huds) species OFFICINALIS (Sole),RUBESCENS (Camus)kind], worldwide known as “Menta di Pancalieri”. This EO, thanks to its high quality, is actually considered by experts to be as one of the best peppermint EO in the world. In this study, we evaluated the antifungal activity of “Menta di Pancalieri” EO either alone or in combination with azole drugs against a wide panel of yeast and dermatophyte clinical isolates. The EO was analysed by GC-MS at Drug Science and Technology Dept., and its antifungal activity (MIC,MFC) was evaluated against 16 Candida spp.,15 non-Candida spp.,and 5 dermatophyte strains (Microsporum canis, M.gypseum, Trichophyton mentagrophytes) according to the CLSI guidelines, with some modifications. The interaction of peppermint EO with azole drugs (fluconazole, itraconazole, ketoconazole) was evaluated through the chequerboard and isobologram methods. The phytochemical composition of peppermint of Pancalieri EO was in agreement with the European Pharmacopoeia. Susceptibility test results suggest this EO exerts a fungicidal activity against yeasts, and a fungistatic activity against dermatophytes. Interaction studies with azole drugs indicate mainly synergistic profiles between itraconazole and peppermint EO vs. Candida spp., Cryptococcus neoformans and T.mentagrophytes. Peppermint of Pancalieri EO may act as a potential antifungal agent and may serve as a natural adjuvant for fungal infection treatment.
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