N STREPPARAVA¹, T WAHLI¹, H SEGNER¹, A CAMINADA², M TONOLLA², O PETRINI<sup>3

1</sup>Department of infectious diseases and pathobiology, Centre for Fish and Wildlife Health, Bern, Switzerland, ²Department of Environment Building and Design, Laboratory of Applied Microbiology, Bellinzona, Switzerland, ³POLE Pharma Consulting, Breganzona, Switzerland

Flavobacterium species are widespread in natural and artificial ecosystems. These species are ubiquitous, opportunistic pathogens that may infect gills, skin, fins and internal organs of a range of injured or immunologically compromised or stressed individuals that are particularly susceptible. Infection often leads to high mortality rates, with large economic losses for fish farmers. Their taxonomy and phylogenetic relationships, however, are still unclear. MALDI-TOF MS is increasingly used in clinical microbiology laboratories to identify bacteria. This study aimed to assess the reliability of MALDI-TOF MS for the identification of Flavobacteria, using the fish pathogenic species F. psychrophilum as an example. We studied 119 Flavobacteriaceae samples including 115 Flavobacterium spp. isolates collected in fish farms in Switzerland and reference strains of F. psychrophilum, F. columnare, F. branchiophilum, F. johnsoniae, F. succinicans, F. frigidimaris, F. pectinovorum, F. aquidurense, F. hercynium, F. fryxellicola, F. limicola, F. psychrolimnae and F. aquatile obtained from culture collections. A dendrogram was prepared using MALDI-TOF MS data and was compared to phylogenetic trees constructed using the 16S rRNA and rpoC gene sequences. The MALDI-TOF MS dendrogram reflected the relationships seen in the 16S rRNA- and rpoC-based phylogenetic trees. Importantly, the MALDI-TOF analysis resulted in an unequivocal grouping of the F. psychrophilum isolates. MALDI-TOF MS can be used to identify Flavobacterium psychrophilum out of complex isolates. Still, the inclusion of additional spectra of well-characterized isolates of other fish pathogenic and environmental species in the MALDI-TOF database is needed. Flavobacterium environmental species are not yet well represented in the different databases, however, use of MALDI-TOF MS technology would implement fast and reliable identification saving time and improving fish management in both wild and fish farm environment.