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Research Project: Integrated Research to Improve On-Farm Animal Health in Salmonid Aquaculture

Location: Cool and Cold Water Aquaculture Research

Title: Genetic diversity of Flavobacterium psychrophilum isolates from three Oncorhynchus spp. in the United States, as revealed by multilocus sequence typing

item VAN VLIET, DANIELLE - Michigan State University
item Wiens, Gregory - Greg
item LOCH, THOMAS - Michigan State University
item NICOLAS, PIERRE - Inra, Génétique Animale Et Biologie Intégrative , Jouy-En-josas, France
item FAISAL, MOHAMED - Michigan State University

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2016
Publication Date: 6/1/2016
Citation: Van Vliet, D., Wiens, G.D., Loch, T.P., Nicolas, P., Faisal, M. 2016. Genetic diversity of Flavobacterium psychrophilum isolates from three Oncorhynchus spp. in the United States, as revealed by multilocus sequence typing. Applied and Environmental Microbiology. 82:3246-3255.

Interpretive Summary: A frequent cause of fish loss at salmonid aquaculture facilities is bacterial cold water disease (BCWD). This disease is caused by the microorganism Flavobacterium psychrophium. This study describes the analysis of 96 Flavobacterium psychrophium isolates obtained from three salmonid species originating from nine states in the USA. To determine the relatedness of the isolates, we utilized multilocus sequence typing (MLST). MLST compares the DNA sequences of internal fragments of seven housekeeping genes amplified and sequenced from each isolate. Different sequences are assigned an allele number and the combination of alleles from an isolate allow assignment of a numerical sequence type (ST) designation. In our study, we identified 34 different ST. This information will be used to more appropriately develop control measures to monitor and reduce the severity of BCWD.

Technical Abstract: Flavobacterium psychrophilum is an important pathogen of salmonids worldwide. Multilocus sequence typing (MLST) has identified a recombinogenic population structure from which emerged a few epidemic clonal complexes particularly threatening for salmonid aquaculture. To date, MLST genotypes for this bacterium have been collected in three major areas of salmonid aquaculture (Europe, Asia, and South America) but information on North America has remained very scarce; in contrast with the historical and economical importance of this area for salmonid farming. Herein, MLST was used to investigate the genetic diversity of 96 F. psychrophilum isolates recovered from three Oncorhynchus spp., namely rainbow trout (O. mykiss), Coho salmon (O. kisutch), and Chinook salmon (O. tshawytscha) originating from nine states of the United States of America. A total of 34 distinct sequence types (STs) clustered in 5 clonal complexes (CCs) or were designated as singletons. The distribution of the STs varied clearly between the three fish hosts. The largest CC was CC-ST10, which included 6 STs recovered exclusively from captive rainbow trout. Although the majority of STs described herein are novel, some STs have previously been found on other continents, and always in the same host fish (e.g., ST10 and ST31 in rainbow trout, and ST9, ST13, and ST30 in Coho salmon). Collectively, this study characterizes widespread and diverse F. psychrophilum lineages within the United States and sheds light on the links between F. psychrophilum populations worldwide.