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Title: Development of a waterborne challenge model for Flavobacterium psychrophilum

Author
item LONG, AMY - University Of Idaho
item FEHRINGER, TYSON - University Of Idaho
item Lafrentz, Benjamin
item CALL, DOUGLAS R. - Washington State University
item CAIN, KENNETH - University Of Idaho

Submitted to: FEMS Microbiology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2014
Publication Date: 10/21/2014
Publication URL: http://handle.nal.usda.gov/10113/60393
Citation: Long, A., Fehringer, T.R., Lafrentz, B.R., Call, D., Cain, K.D. 2014. Development of a waterborne challenge model for Flavobacterium psychrophilum. FEMS Microbiology Letters. 359:154-160.

Interpretive Summary: Flavobacterium psychrophilum is a bacterial fish pathogen that can greatly impact the aquaculture production of salmonid fish such as rainbow trout and coho salmon. Laboratory research efforts are focused on developing improved methods for disease prevention. Such research involves administering a treatment to the fish (such as a vaccine) and then artificially infecting the fish with the pathogen to determine if the treatment provides any protection from the pathogen. The method most commonly used for artificially infecting the fish is injection of the pathogen into the fish. This method is reproducible; however, it does not mimic a natural infection that would occur in the fish under normal production conditions. Although it is not possible to completely mimic a natural infection in laboratory studies, a reproducible method that entails exposing fish to the pathogen through the water is needed and would represent an improvement over an injection method. In this study, we describe a waterborne method of artificially infecting rainbow trout with F. psychrophilum which combines inducing minor skin disruptions to fish and growing the bacteria in iron-limited media. Although further optimization is needed, this method more closely mimics a natural infection. Thus use of it in laboratory studies testing disease prevention strategies may provide more meaningful information concerning how the strategy may perform under normal production conditions.

Technical Abstract: Flavobacterium psychrophilum is the causative agent of bacterial coldwater disease and can cause significant mortality in salmonid aquaculture. To better evaluate disease prevention or treatment methods for F. psychrophilum in the laboratory, a waterborne challenge model that mimics a natural outbreak is needed. Here we report on the development of a waterborne challenge model for F. psychrophilum in which we incorporated variables that may influence challenge success, specifically scarification prior to bacterial exposure and culture of F. psychrophilum under iron-limited culture conditions to potentially increase the probability of establishing disease. Additionally, two F. psychrophilum isolates, CSF 259-93 and THC 02-90, were used in this model to test if there were virulence differences between isolates. Mortality was significantly higher (P < 0.05) in scarred fish supporting the hypothesis that disruptions in the dermal layer are necessary for a successful waterborne challenge. Although mortality differences were not significant between iron-replete and iron-limited treatments, mortality was high overall, > 30%. There was a significant difference in mortality between CSF 259-93 and THC 02-90 treatments (P < 0.05) although both isolates cause high mortality in injection challenges. In conclusion, this waterborne challenge model can be used to evaluate potential disease prevention and treatment methods.