Abstract
The aim of this study was to evaluate the influence of tea tree oil (TTO) and “Mentha of Pancalieri” essential oil (MPP) on intracellular killing of Candida krusei, often resistant to conventional drugs, by polymorphonuclear leucocytes (PMNs). Intracellular killing was investigated by incubating yeasts and PMNs with essential oils (EOs) at 1/4 and 1/8 × MIC (Minimal Inhibitory Concentration), in comparison with anidulafungin, used as a reference drug. Killing values were expressed as Survival Index (SI) values. The cytotoxicity of EOs was evaluated by 3-[4,-5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Both EOs were more efficaceous at 1/8 × MIC than 1/4 × MIC, with killing values higher than observed in EO-free systems and in presence of anidulafungin, indicating that the decreasing concentrations did not cause lower candidacidal activity. This better activity at 1/8 × MIC is probably due to the EOs’ toxicity at 1/4 × MIC, suggesting that at higher concentrations EOs might interfere with PMNs functionality. TTO and MPP at 1/8 × MIC significantly increased intracellular killing by PMNs through their direct action on the yeasts (both EOs) or on phagocytic cells (MPP), suggesting a positive interaction between EOs and PMNs to eradicate intracellular C. krusei. These data showed a promising potential application of TTO and “Mentha of Pancalieri” EO as natural adjuvants in C. krusei infection management.
Highlights
The growing threat of antimicrobial drug resistance to conventional antimicrobial drugs has stimulated the search for new therapeutic alternatives, including many extracts of medicinal plants and essential oils (EOs) that are well recognized for their potential antimicrobial role against microorganisms [1,2]
The purpose of this study was to evaluate the influence of the tea tree (Melaleuca alternifolia) oil (TTO) and the “Mentha of Pancalieri” (MPP) EO on intracellular killing by human polymorphonuclear leucocytes (PMNs), the first cell line of host defence, against Candida krusei, a yeast pathogen usual resistant to conventional drugs, in comparison with anidulafungin (AND), one of the antifungal drugs used in candidiasis management
Comparison of MIC data demonstrated that both TTO and MPP EO displayed low MICs (% v/v) with a standard yeast inoculum of 103 cfu/mL and possessed a significant fungicidal activity against C.krusei
Summary
The growing threat of antimicrobial drug resistance to conventional antimicrobial drugs has stimulated the search for new therapeutic alternatives, including many extracts of medicinal plants and essential oils (EOs) that are well recognized for their potential antimicrobial role against microorganisms [1,2]. Clinical experience showed that the efficacy of conventional antimicrobial drugs depends both on their direct effect on microorganisms and on the activity of the host immune system to find compounds. To make a valid assessment of EOs activity for use in pharmaceutical applications and an effective comparison with conventional drugs, it is important to evaluate the classic microbiological parameters for assessing the antimicrobial efficacy and the influence of the EOs on host defence mechanisms. The identification of substances, other than antibiotics, that can positively modulate these phagocytes is of great interest [7]
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