Genus‐level identification of dermatophytes by MALDI‐TOF MS after 2 days of colony growth

Matrix‐assisted laser desorption‐ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) is becoming a popular technology in clinical microbiology. It is a fast and highly specific method for the routine identification of micro‐organisms. In this study, we evaluated the suitability of dermatophyte identification after only 2 days of colony growth using MALDI‐TOF MS. Two protein extraction protocols were also evaluated consisting of either formic acid alone or of ethanol‐formic acid‐acetonitrile to achieve a complete protein extraction. Morphology‐based techniques were used as the diagnostic standard methods and MALDI‐TOF MS results were obtained using the manufacturer's spectral library. Using the formic acid protein extraction protocol after 2 days of colony growth, 70 and 46% of dermatophytes were properly identified at the genus and species‐level respectively. The addition of ethanol‐formic acid‐acetonitrile extraction protocol increased the identification to 90 and 62%. Based on our observations, we propose a two‐step workflow for the fast and reliable identification of dermatophytes after only 2 days of colony growth. This flow chart consists of a first direct deposition procedure with the addition of formic acid, followed by a complete protein extraction when dermatophyte identification is not successful.

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