Interlaboratory Proficiency Test Using MALDI-TOF MS for Identification of Food-Associated Bacteria

An interlaboratory proficiency test using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify food-associated bacteria was performed with 16 food microbiological laboratories, comprising ten authorities, four companies, and two academic institutions using either the Bruker Daltonics MALDI Biotyper system, the VITEK MS Ruo SARAMIS, VITEK MS IVD Ruo (bioMerieux, France) or PAPMID (Mabritec AG, Switzerland). A blinded set of 15 reference strains was selected from the Bavarian Health and Food Safety Authority strain collection, comprising common food-associated bacteria. Depending on the presence in the databases and appropriate interpretation of data, mean accuracy rates between 34 and 100% were achieved for the respective bacterial species. Percentages of correct identifications were compared independence of the platform and the databases used. The influence of the sample preparation method and interpretation of results were also considered. Our results showed that the platform itself had no significant impact on credit points achieved. The use of an adequate sample preparation method, as well as correct interpretation of results, was much more decisive for the results achieved. In-house databases improved correct identifications when the demanded species was not mapped in the commercial databases.