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MALDI-TOF MS for species identification in single laboratories or laboratory networks

Guidelines for the validation of identifications of taxonomically defined species using MALDI-TOF MS in such laboratories have been published in Germany. Here, Jörg Rau outlines the basics of what you need to know.

In food microbiology or veterinary diagnostics, MALDI-TOF MS already has a central role in many laboratories. Further applications, such as the identification of animal species in meat or cheese by means of user-made databases, were also developed by labs interested in food control. In general, MALDI‑TOF MS is operated with several goals: as a qualitative method for non-directed identification (screening), for the identification of concrete microbial parameters, or as a confirmation test eg, for relevant bacterial pathogens.

MALDI‑TOF MS systems generate mass spectra of biomolecules (eg, proteins) of unknown samples. These mass spectra are compared with reference spectral patterns organised in databases. Through a computer-aided ranking of the best match with the reference patterns, and the application of empirical decision rules, the sample is assigned a taxonomic level, like species or genus, and thus identified. A well sorted, fitting and maintained database is vital for reliable and successful identification.

For such previously non-standardised solutions and technologies, method validations are particularly relevant for laboratories. Validations are intended to prove the usability of the methods for the respective application. Therefore, in 2021, a German expert group published guidelines for the validation of identifications of taxonomically defined species (eg, bacteria, fungi or animal species) using MALDI-TOF MS in single laboratories or laboratory networks.1,2

In this article, we introduce a selection of ideas and criteria and briefly summarise them from the user’s perspective.