Epidemiological cutoff values for four clinical antifungal drugs against Malassezia furfur. Preliminary estimated data.

ROJAS, FLORENCIA D.; SOSA, MARÍA A.; MUSSIN, JAVIER E.; LATORRE, WENCESALO E.; ALEGRE, LILIANA; GIUSIANO, GE

Amsterdam

Workshop; Workshop Malassezia. 20th Congress of the International Society for Human and Animal Mycology; 2018

International Society for Human and Animal Mycology

Objectives: To estimate epidemiological cutoff values (ECVs) of fluconazole (FZ), voriconazole (VZ) and amphotericin B (AB) for Malassezia furfur.Material and methods. Minimal inhibitory concentration (MIC) of FZ, VZ and AB against 63 M. furfur clinical isolates was determined according to CLSI M27‐A3 reference document, with some modifications for support optimal growth of these lipo-dependent yeasts. ECVs were calculated using ECOFFinder MS Excel spreadsheet calculator considering the modal MIC, the MIC distribution, the assumption that the wild type (WT) population should cover three to five 2-fold dilutions around the modal MIC and that the ECV should include at least 95% of WT organisms. Strains with MICs ≤ ECVs were classified as WT strains, and those with MICs > ECVs were classified as non-WT strains.Results: All MIC distributions covered three to five 2-fold dilution steps surrounding the modal MIC. Table 1 shows (ECVs) for FZ, VZ and AB against 63 M. furfur isolates. Antifungal drugECV (µg/mL)Probability to harbor resistance% of non-WT isolatesWTNon-WTAmphotericin B≤ 16≥ 3299.05%4.90%≤ 32≥ 6499.9%0.00%Fluconazole≤ 64≥ 12899.05%3.20%Itraconazole≤ 0.06≥ 0.12595.01%6.80%Voriconazole≤ 0.06≥1.099.9%5.40%Conclusion: The role of the ECV is to discriminate WT from non-WT isolates. Non-WT isolates harbor intrinsic or acquired resistance mechanisms, which most often correlate with high MIC above the ECV for the species/agent corresponding. These values do not categorize a fungal isolate as susceptible or resistant as breakpoints do, that is because do not take into account antifungal agent pharmacology or clinical outcome findings. These cut off values may, with due caution, aid physicians in managing mycosis by species where breakpoints are not available, as in the case of Malassezia genus. Certain conditions have not been fulfilled when this statistical analysis was applied in the estimation of M. furfur ECVs, such as, the number of strains studied and that there should be more participating laboratories. The strict requirements and difficulties to growth and maintenance of Malassezia yeast lead to a few susceptibility studies carried out using a microdilution method based on the CLSI methodology. Moreover, few laboratories study Malassezia susceptibility using the same methodology, limiting comparison of the results and make difficult to carry out collaborative studies. Anyway, this study presents the first approach to estimate ECVs for M. furfur.Both Malassezia species showed high ECVs for FZ and AB. These are first-line drugs for treatment of systemic infection by Malassezia species. These high values could indicate intrinsic resistance of this species or potentially harbor acquired resistance mechanisms. Molecular techniques would allow validating these ECVs estimated from phenotypic data. Use a standardized technique is the first requirement in order to optimize the susceptibility data collection of these fastidious yeasts; in addition, molecular studies on mechanisms of resistance need to be examined. Collaborative investigations are required that allow set up susceptibility cut-off values of these Malassezia yeasts.