Possibilities of dermatophyte identification with the MALDI Biotyper – new and old approaches
Moulds and dermatophytes keep appearing more frequently in the microbiological routine. The diagnosis of mould infections is often based on morphological criteria. These may encounter time-consuming sporulation as a prerequisite for identification. Based on this, molecular methods like DNA sequencing are more frequently used for identification to species and/or genus level.
MALDI-TOF MS has improved microbial identification, especially of yeasts and bacteria, dramatically in recent years. The identification of filamentous fungi and dermatophytes by MALDI has not increased as fast due to e.g. difficulties in handling and databases with limited entries. However, MALDI shows a high species resolution similar to sequencing and is faster. Here we give an overview of the current state and possibilities of identifying filamentous fungi and dermatophytes with the MALDI Biotyper, MBT (Bruker Daltonik, Bremen). Samples can either be identified directly from an agar plate, applying a protein extraction step using material from the agar plate or applying a protein extraction step from liquid cultivation. Depending on the growth behaviour of the fungus, the most suitable identification approach can be chosen. Identification success with the MALDI Biotyper also depends on the quality of the acquired spectra. Hence using a new spectrum acquisition method enables the performance of more direct identification approach and efficient measurements of samples, which will be also presented here.
As mentioned, besides the preparation and acquisition method used, the MALDI library plays an important role. In the past years, the commercially available MBT RUO filamentous fungus library has been expanded, starting from 364 database entries (44 dermatophytes, comprising 13 different dermatophyte species) to the current 786 entries (124 dermatophytes with 33 different dermatophytes). The current dermatophyte species can be divided into about 25 separate species, with the genus Trichophyton as the largest coherent group.
Since the taxonomy in filamentous fungi and dermatophytes is rapidly evolving, cooperation with various groups interested in the identification of fungi is highly appreciated. To provide an up-to-date and wide-ranging database, impact from the scientific community is necessary.