"The fish pathogen, Flavobacterium psychrophilum, has caused substantial economic losses, particularly to farm/hatchery reared salmonids on at least five continents. F. psychrophilum genetic diversity has been explored using several techniques, including multilocus sequence typing (MLST), which has proven to be superior to other molecular typing assays. Although isolates of F. psychrophilum have been MLST genotyped in Europe, Asia, and South America, the genetic diversity of North American (NA) F. psychrophilum is largely unexplored. To address this knowledge gap, I genotyped 314 F. psychrophilum isolates that were recovered from 20 US states and 1 Canadian province from 10 fish species over nearly 4 decades, which revealed 66 sequence types (STs), 47 of which were novel, and 7 novel clonal complexes (CCs). CC-ST10 was the predominant CC in NA and its genotypes were recovered from rainbow trout/steelhead (Oncorhynchus mykiss) from nearly every sampled state. Several other CCs were also discovered, some of which appeared host specific, whereas others appeared to be "generalists". Recombination is hypothesized to have caused most variations among isolates of this study, although the mechanism by which this occurs remains unknown. To explore CC-ST10 pathogenicity in rainbow trout, I intramuscularly injected juvenile rainbow trout with several of its genotypes and compared them to the world's second largest CC, CC-ST191, which resulted in significant mortality. Overall, both CC-ST10 and CC-ST191 were highly pathogenic to rainbow trout, yet significant differences in mean times to death were observed among the genotypes."--Abstract.
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