22Bacteria from the genus Flavobacteriaceae often show low susceptibility to antibiotics. With the 23 exception of two Chryseobacterium spp. isolates that were positive for the florfenicol resistance 24 gene floR, no clinical resistance genes were identified by microarray in 36 Flavobacteriaceae isolates 25 from salmonid fish that could grow in ≥ 4 mg/L florfenicol. Whole genome sequence analysis of the 26 floR positive isolates revealed the presence of a region that contained the antimicrobial resistance 27 (AMR) genes floR, a tet(X) tetracycline resistance gene, a streptothricin resistance gene and a 28 chloramphenicol acetyltransferase gene. In silico analysis of 377 published genomes for 29Flavobacteriaceae isolates from a range of sources, confirmed that well-characterized resistance 30 gene cassettes were not widely distributed in bacteria from this group. Efflux pump-mediated 31 decreased susceptibility to a range of antimicrobials was confirmed in both floR positive isolates 32 using an efflux pump inhibitor (phenylalanine-arginine β-naphthylamide) assay. The floR isolates 33 possessed putative virulence factors, including production of siderophores and, haemolysins, and 34 were mildly pathogenic in rainbow trout. Results support the suggestion that, despite the detection 35 of floR, susceptibility to antimicrobials in Flavobacteriaceae is mostly mediated via intrinsic 36 mechanisms rather than the horizontally acquired resistance genes more normally associated with 37Gram-negative bacterial pathogens such as Enterobacteriaceae. 38 39