Phylogenetic and genomic insights of Flavobacterium diversity in Quebec's fish farms.

The genus Flavobacterium constitutes a vast pool of microorganisms living in multiple environmental niches including fish pathogens and species in the fish microbiome. Veterinary reports have identified flavobacteria in fish from Quebec's fish farms, confirming their association with infections. However, these reports have not conducted in-depth characterization, and the diversity of nonpathogenic flavobacteria in Quebec remains unknown. This study is the first step in assessing the diversity of Flavobacterium in Quebec's fish farms, without focusing solely on pathogenic strains. Seventeen isolates were collected from different fish farms, from either the water or fish. Microbial species identification was performed using PCR genotyping of the gyrB gene, whole-genome sequencing, and phylogenetic analysis. Antimicrobial susceptibility tests for tetracycline and florfenicol, the two most commonly used antibiotics in Quebec aquaculture, along with predictive tools, were employed to assess resistance. This study revealed potential new species among the isolates. No known pathogenic species were detected, and all 17 isolates clustered within CIIIb or CIIIc, recently described phylogenetic clades of Flavobacterium found in various environments, and the majority showed resistance to antibiotics. This study highlights the expanding diversity of Flavobacterium, particularly among species associated with fish, and underscores the need for further research in Quebec.