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bioRxiv · 10.1101/2023.02.23.529686

Interplay between a bacterial pathogen and its host in rainbow trout isogenic lines with contrasted susceptibility to Cold Water Disease

Lee, B.-H.·Quillet, E.·Rigaudeau, D.·Dechamp, N.·Duchaud, E.·Bernardet, J.-F.·Boudinot, P.·Rochat, T.
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Abstract

Infectious diseases are a major constraint on aquaculture. Genetic lines with different susceptibilities to diseases are useful models to identify resistance mechanisms to pathogens and to improve prophylaxis. Bacterial cold-water disease (BCWD) caused by Flavobacterium psychrophilum represents a major threat for freshwater salmonid farming worldwide. A collection of rainbow trout (Oncorhynchus mykiss) isogenic lines was previously produced from a French domestic population. Here, we compared BCWD resistance phenotypes using a subset of isogenic lines chosen for their contrasted susceptibilities to F. psychrophilum. We applied individual monitoring to document the infection process, including time-course quantification of bacteremia and innate immune response. Strikingly, BCWD resistance was correlated with a lower bacterial growth rate in blood. Several immune genes were expressed at higher levels in resistant fish regardless of infection: the Type II arginase (arg2), a marker for M2 macrophages involved in anti-inflammatory responses and tissue repair, and two Toll-like receptors (tlr2/tlr7), responsible for pathogen detection and inflammatory responses. This study highlights the importance of innate and intrinsic defense mechanisms in determining the outcome of F. psychrophilum infections, and illustrates that non-lethal time-course blood sampling for individual monitoring of bacteremia is a powerful tool to resolve within-host pathogen behavior in bacterial fish diseases.

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Lee, B.-H., Quillet, E., Rigaudeau, D., Dechamp, N., Duchaud, E., Bernardet, J.-F., Boudinot, P., Rochat, T.. 2023-02-23. Interplay between a bacterial pathogen and its host in rainbow trout isogenic lines with contrasted susceptibility to Cold Water Disease. https://doi.org/10.1101/2023.02.23.529686

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