[The Effect of Different Media on MALDI-TOF MS Analysis Data Based on the Composite Correlation Index of Malassezia...

Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is widely used in microbiology. Composite index (CI) analyses, which involve evaluating spectra obtained from the device as well as small peak data, are a crucial method for examining microbial differences. When analysing the impact of external factors on cell composition, the composite correlation index (CCI) facilitates the grouping of spectrum data. In recent years, a significant increase in the isolation of Malassezia furfur strains from clinical specimens has been observed. Due to its lipid-dependent growth characteristics, this pathogen does not grow on the media typically used in routine mycology, such as Sabouraud’s dextrose agar. It is therefore recommended that each laboratory prepare and use its own appropriate media when necessary. However, the contents and their quantities in media used to cultivate Malassezia yeasts can vary considerably. Modified Dixon agar (mDA), modified Leeming & Notman agar (mLNA) and Fast Fung agar (FFA) are widely used as both primary culture media and in research. The variation in the composition of these media may lead to different spectra forming. This study aimed to investigate the relationship between MALDI-TOF MS spectra obtained from cultivating lipophilic M.furfur strains on different media and to assess their usability in routine practice. Seventeen M.furfur isolates included in the study were grown on mDA, mLNA and FFA agar. CI analyses of MALDI-TOF MS spectra of the strains were performed and CCI data were compared. While no difference was found in the CI values of the FFA and mLNA media for the strains included in the study (p> 0.05), the CI values of both media were higher than those of the mDA media (p< 0.05). Kurtosis values for the media were calculated as 1.83, -0.56, and -1.16, respectively, for FFA, mLNA and mDA. The platykurtic distribution of the mDA medium data in the study suggests that, despite its widespread use, it may lead to time-consuming spectroscopic analyses. The high CI values observed in FFA and mLNA media prepared with tween 60 indicate that methods such as MALDI-TOF MS are more suitable for standardization in the analysis of M.furfur. Differences in tween will also affect the efficiency of tween removal protocols in MALDI-TOF MS analyses. The acquisition of variable data and the requirement to process minor spectral parameters, such as CI values, underscore the importance of standardizing culture media protocols. Achieving consistency in media formulation will further support the generation of comparable data between laboratories.