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MALDI-TOF MS as a tool to identify foodborne yeasts and yeast-like fungi

Quintilla, Raquel, Kolecka, Anna, Casaregola, Serge, Daniel, Heide M., Houbraken, Jos, Kostrzewa, Markus, Boekhout, Teun, Groenewald, Marizeth
International journal of food microbiology 2018 v.266 pp. 109-118
Candida oleophila, Candida sake, Clavispora lusitaniae, Debaryomyces hansenii, Kazachstania, Meyerozyma caribbica, Mrakia, Pichia membranifaciens, Rhodotorula, databases, financial economics, food industry, food spoilage, matrix-assisted laser desorption-ionization mass spectrometry, sibling species, yeasts
Since food spoilage by yeasts causes high economic losses, fast and accurate identifications of yeasts associated with food and food-related products are important for the food industry. In this study the efficiency of the matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify food related yeasts was evaluated.A CBS in-house MALDI-TOF MS database was created and later challenged with a blinded test set of 146 yeast strains obtained from food and food related products. Ninety eight percent of the strains were correctly identified with log score values>1.7. One strain, Mrakia frigida, gained a correct identification with a score value<1.7. Two strains could not be identified at first as they represented a mix of two different species. These mixes were Rhodotorula babjevae with Meyerozyma caribbica and Clavispora lusitaniae with Debaryomyces hansenii. After separation, all four species could be correctly identified with scores>1.7. Ambiguous identifications were observed due to two incorrect reference mass spectra's found in the commercial database BDAL v.4.0, namely Candida sake DSM 70763 which was re-identified as Candida oleophila, and Candida inconspicua DSM 70631 which was re-identified as Pichia membranifaciens. MALDI-TOF MS can distinguish between most of the species, but for some species complexes, such as the Kazachstania telluris and Mrakia frigida complexes, MALDI-TOF MS showed limited resolution and identification of sibling species was sometimes problematic. Despite this, we showed that the MALDI-TOF MS is applicable for routine identification and validation of foodborne yeasts, but a further update of the commercial reference databases is needed.