P0320 Positive influence of tea tree oil on human PMN intracellular killing against Candida krusei

Narcisa Mandras1, Janira Roana*1, Daniela Scalas1, Anna Luganini4, Fabrizio D'amico1, Valeria Ghisetti3, Mario Rosario Rizzi2, Anna Maria Cuffini1, Vivian Tullio1

1University of Turin, Public Health and Pediatrics Department, 2Flora, Pisa, Italy, Pisa, Italy, 3Amedeo di Savoia Hospital, Turin, Microbiology and Virology Laboratory, Turin, Italy, 4University of Turin, Life Sciences and Systems Biology Department

Background: The growing threat of antimicrobial drug resistance has stimulated the search for new therapeutic alternatives, including essential oils that are now recognized for their potential antimicrobial role against microorganisms. The essential oil (EO) of Melaleuca alternifolia (Myrtaceae; Tea Tree Oil) was used early in last century to treat many pathological conditions, predominantly dermatoses (e.g., recurrent herpes labialis, acne, pustules, dandruff, and rash). Moreover, Tea Tree Oil (TTO) has recently received much attention for its antibacterial, antifungal and antiviral properties. Since clinical experience showed that the efficacy of antimicrobial drugs depends both on their direct effect on microorganisms and on the activity of the host immune system, the aim of the study was to evaluated the influence of TTO, at subinhibitory concentrations, on intracellular killing by PMNs against Candida krusei, in comparison with anidulafungin (AND), one of the antifungal drugs used in candidiasis management.

Materials/methods: A clinical C.krusei strain was used. The EO was purchased from Flora, Pisa, Italy, and analysed by GC (Drug Science and Technology Dept., University of Turin). AND was provided by Pfizer Italia.

Susceptibility testing was based on the CLSI M27-A3 method, with some modifications for EO. Intracellular killing was investigated by incubating yeasts (106 cfu/mL) and PMNs (106cells/mL) at 37°C for 30, 60, 90 min in presence of TTO subinhibitory concentrations (1/4 and 1/8 MIC), and 1/2MIC of AND. Killing values were expressed as Survival Index. EO/AND-free controls were included. Statistical evaluation of the differences between test and control results was performed by Tukey’s test. The cytotoxicity of various concentrations of TTO was evaluated with MTT test assay.

Results: TTO was more efficacy at ⅛ MIC than ¼ MIC, with killing values higher in comparison with those observed in free-EO systems and in presence of AND, indicating that the decreasing concentrations did not cause lower candidacidal activity. Moreover, TTO at 1/4 MIC was toxic, with decreased intracellular killing values, suggesting that TTO at higher concentrations could interfere with the functionality of PMNs.

Conclusions: These data show a promising potential application of TTO, as natural adjuvant against C.krusei, often resistant to conventional drugs.