Antifungal susceptibility testing of Malassezia yeast: comparison of two different methodologies

Abstract

All Malassezia species are lipophilic; thus, modifications are required in susceptibility testing methods to ensure their growth. Antifungal susceptibility of Malassezia species using agar and broth dilution methods has been studied. Currently, few tests using disc diffusion methods are being performed. The aim was to evaluate the in vitro susceptibility of Malassezia yeast against antifungal agents using broth microdilution and disc diffusion methods, then to compare both methodologies. Fifty Malassezia isolates were studied. Microdilution method was performed as described in reference document and agar diffusion test was performed using antifungal tablets and discs. To support growth, culture media were supplemented. To correlate methods, linear regression analysis and categorical agreement was determined. The strongest linear association was observed for fluconazole and miconazole. The highest agreement between both methods was observed for itraconazole and voriconazole and the lowest for amphotericin B and fluconazole. Although modifications made to disc diffusion method allowed to obtain susceptibility data for Malassezia yeast, variables cannot be associated through a linear correlation model, indicating that inhibition zone values cannot predict MIC value. According to the results, disc diffusion assay may not represent an alternative to determine antifungal susceptibility of Malassezia yeast.

Antifungal Susceptibility of Malassezia Species Isolated From Pityriasis Versicolor Cases

“…[15] The good in vitro activity of itraconazole shown in this study makes it a possible choice for the treatment of Malassezia related infections in this particular geographic area. In agreement with other reports, this study also found higher in vitro antifungal activity against all the tested clinical isolates of Malassezia spp, with itraconazole.…”

“…These results are similar to or higher than those documented in various other studies. [15,18,19] MIC ranges against itraconazole shown in several studies are as follows: < 0.03-16µg/mL, [16] 0.007 -0.05μg/mL, [19] 3µg/mL -0.125µg/mL [6] and ≤ 0.03 -0.06 µg/mL. [4] Gupta AK et al [17] found the MIC data obtained for itraconazole were similar to MICs for itraconazole and ketoconazole with an MIC of 0.8µg/ml for both.…”

“…The ketoconazole MICs range from ≤ 0.03 -8 μg/mL with all the species tested, These values are similar to or higher than those documented in other studies. [14,15,8,17] Garau M et al [8] registered MICs of ≤0.03µg/mL against 70 isolates of Malassezia. Gupta AK et al [15] demonstrated that out of 55 of strains of Malassezia the MIC ranges as ≤ 0.03µg/mL -0.125μg/mL with 95% of them having an MIC of ≤ 0.03μg/mL.…”

“…[14,15,8,17] Garau M et al [8] registered MICs of ≤0.03µg/mL against 70 isolates of Malassezia. Gupta AK et al [15] demonstrated that out of 55 of strains of Malassezia the MIC ranges as ≤ 0.03µg/mL -0.125μg/mL with 95% of them having an MIC of ≤ 0.03μg/mL. This study is in contrast with the above mentioned studies as four M. furfur strains showed an increased MIC of 8μg/mL.…”

“…The overall MICs range for fluconazole, itraconazole and ketoconazole were ≤ 0.125-16μg/mL, ≤ 0.03-1µg/mL and ≤ 0.03-8µg/mL respectively. When all the strains were considered together, this [14,15] Hence, studying Malassezia susceptibility might provide better information about the susceptibility pattern of different species. The ketoconazole MICs range from ≤ 0.03 -8 μg/mL with all the species tested, These values are similar to or higher than those documented in other studies.…”