Abstract
The epidemiology of yeast infections and resistance to available antifungal drugs are rapidly increasing, and non-albicans Candida species and rare yeast species are increasingly emerging as major opportunistic pathogens. In order to identify new strategies to counter the threat of antimicrobial resistant microorganisms, essential oils (EOs) have become an important potential in the treatment of fungal infections. EOs and their bioactive pure compounds have been found to exhibit a wide range of remarkable biological activities. We investigated the in vitro antifungal activity of nine commercial EOs such as Thymus vulgaris (thyme red), Origanum vulgare (oregano), Lavandula vera (lavender), Pinus sylvestris (pine), Foeniculum vulgare (fennel), Melissa officinalis (lemon balm), Salvia officinalis (sage), Eugenia caryophyllata (clove) and Pelargonium asperum (geranium), and some of their main components (α-pinene, carvacrol, citronellal, eugenol, γ-terpinene, linalool, linalylacetate, terpinen-4-ol, thymol) against non-albicans Candida strains and uncommon yeasts. The EOs were analyzed by GC-MS, and their antifungal properties were evaluated by minimum inhibitory concentration and minimum fungicidal concentration parameters, in accordance with CLSI guidelines, with some modifications for EOs. Pine exhibited strong antifungal activity against the selected non-albicans Candida isolates and uncommon yeasts. In addition, lemon balm EOs and α-pinene exhibited strong antifungal activity against the selected non-albicans Candida yeasts. Thymol inhibited the growth of all uncommon yeasts. These data showed a promising potential application of EOs as natural adjuvant for management of infections by emerging non-albicans Candida species and uncommon pathogenic yeasts.
Highlights
To date, the majority of fungal infections in humans are still due to Candida albicans (63–70%)
The chemical compositions of F. vulgare, L. vera, M. officinalis, P. sylvestris, S. officinalis, T. vulgaris, E. caryophyllata, O. vulgare, and P. asperum essential oils (EOs) are presented in Table 1, in according to data gathered from GC-MS and GC-FID phytochemical analyses
Pinus sylvestris (Pine) and lemon balm EOs exhibited strong antifungal activity against the selected non-albicans Candida yeast pathogens, with Minimum inhibitory concentration (MIC) ranges of 0.03–0.12% (v/v), even against the FLC-resistant and/or VRC-resistant Candida strains (C. krusei, C. norvegensis and C. valida, respectively) (Table 2)
Summary
The majority of fungal infections in humans are still due to Candida albicans (63–70%). Other Candida species, such as C. krusei and C. parapsilosis, Cryptococcus neoformans and other uncommon yeasts, usually found in the environment and as skin or mucosal colonizers in humans, are emerging as opportunistic pathogens [1,2,3]. C. parapsilosis is currently one of the leading species of catheter-related candidemia and fungal infections in neonates and patients in intensive care units. Other rare yeast species such as Sporobolomyces spp. have been reported as a cause of sporadic invasive bloodstream infections in patients in intensive care units and with central venous catheters, as well as in AIDS patients [6]. Some common species, such as Saccharomyces cerevisiae can be responsible for uncommon clinical cases This yeast is generally considered a safe organism very useful in agro-alimentary and pharmaceutical fields. Several isolates have shown virulence features, being able to produce opportunistic infections, mainly in immunodeficient patients [6]
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