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Title: Flavobacterium columnare genomovar influences mortality in channel catfish (Ictalurus puncatus)

Author
item Shoemaker, Craig
item OLIVARES-FUSTER, OSCAR - AUBURN UNIVERSITY
item ARIAS, COVA - AUBURN UNIVERSITY
item Klesius, Phillip

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2007
Publication Date: 1/20/2008
Citation: Shoemaker, C.A., Olivares-Fuster, O., Arias, C.R., Klesius, P.H. 2008. Flavobacterium columnare genomovar influences mortality in channel catfish (Ictalurus puncatus). Veterinary Microbiology 127: 353-359.

Interpretive Summary: Genetic diversity has been documented and confirmed in Flavobacterium columnare, causal agent of columnaris disease. This aquatic bacterium is pathogenic to many species of freshwater fish throughout the world, and the United States channel catfish (Ictalurus punctatus) aquaculture industry is severely impacted by columnaris disease. The majority of the F. columnare isolates recovered from diseased channel catfish belonged to two genetic groups (either genomovar I or II). The objective of the present study was to determine if differences existed in the ability of these genomovars to cause disease in channel catfish. We were able to show that genomovar II isolates were more virulent for young catfish and that the ability of these isolates to stick (adhere) to the surface of the fish was higher. Our results suggest that although both genomovars are present in the aquatic environment and routinely isolated from channel catfish with columnaris disease, genomovar II appears to be more pathogenic (virulent) for channel catfish.

Technical Abstract: Genetic diversity has been documented and confirmed in Flavobacterium columnare, causal agent of columnaris disease. This aquatic bacterium is pathogenic to many species of freshwater fish throughout the world, and the United States channel catfish (Ictalurus punctatus) aquaculture industry is severely impacted by columnaris disease. The majority of the F. columnare isolates recovered from diseased channel catfish belonged to either genomovars I or II. The objective of the present study was to determine if differences existed in the ability of these genomovars to induce mortality in channel catfish. Single strand conformation polymorphism analysis (SSCP) was used to ascribe the isolates used in this study to the appropriate genomovar. Immersion challenge experiments, 15 minute immersion exposure to about one million, were carried out to assess virulence of genomovar I and II isolates to channel catfish. The results demonstrated genomovar II isolates were significantly (P < 0.05) more virulent in channel catfish fry (92-100% mortality) than genomovar I isolates (0-46% mortality). Genomovar effect in fingerling channel catfish was also significant (P < 0.05) with genomovar II resulting in greater mortality (74.7 % versus 30.2 %). In vivo adhesion of the genetically characterized F. columnare was also strongly correlated to increased mortality in the challenged catfish.