Identification of Francisella tularensis Subspecies in a Clinical Setting Using MALDI-TOF MS: An In-House Francisella Library and Biomarkers

is a zoonotic bacterium that is endemic in large parts of the world. It is absent in the standard library of the most applied matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) systems: the Vitek MS and the Bruker Biotyper system. The additional Bruker MALDI Biotyper Security library contains without subspecies differentiation. The virulence of differs between the subspecies. The subspecies (ssp.) is highly pathogenic, whereas the subspecies displays lower virulence and subspecies and ssp. are hardly virulent. To differentiate the and the -subspecies, an in-house library was built with the Bruker Biotyper system and validated together with the existing Bruker databases. In addition, specific biomarkers were defined based on the main spectra of the strains supplemented with in silico genome data. Our in-house library accurately differentiates the subspecies and the other . The biomarkers correctly differentiate the various species within the genus and the subspecies. These MALDI-TOF MS strategies can successfully be applied in a clinical laboratory setting as a fast and specific method to identify to subspecies level.