Coinfection of channel catfish (Ictalurus punctatus) with virulent Aeromonas hydrophila and Flavobacterium covae exacerbates mortality

Authors: WISE, ALLISON - Auburn University; Lafrentz, Benjamin; KELLY, ANITA - Auburn University; LILES, MARK - Auburn University; GRIFFIN, MATT - Mississippi State University; Beck, Benjamin; BRUCE, TIMOTHY - Auburn University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2023
Publication Date: 1/12/2024
Citation: Wise, A.L., Lafrentz, B.R., Kelly, A.M., Liles, M.R., Griffin, M.J., Beck, B.H., Bruce, T.J. 2024. Coinfection of channel catfish (Ictalurus punctatus) with virulent Aeromonas hydrophila and Flavobacterium covae exacerbates mortality. Journal of Fish Diseases. 2024:e13912. https://doi.org/10.1111/jfd.13912.
DOI: https://doi.org/10.1111/jfd.13912

Interpretive Summary: Flavobacterium covae and virulent Aeromonas hydrophila are prevalent bacterial pathogens within the U.S. catfish industry that can cause high mortality in production ponds. Coinfections between these two pathogens potentially augment mortality causing catastrophic economic losses. In order to evaluate both the immunological effects and the effects coinfections have on mortality, Flavobacterium covae and virulent Aeromonas hydrophila were concurrently exposed to channel catfish. Catfish were divided into seven treatments: 1) mock control; 2 and 3) high and low doses of virulent A. hydrophila; 4 and 5) high and low doses of F. covae; 6 and 7) simultaneous challenge with high and low doses of virulent A. hydrophila and F. covae. Cumulative percent mortality, bacterial load, lysozyme activity, and gene expression were evaluated during the experimental challenge. The results demonstrated the additive effects on mortality when these two pathogens are combined. The synthesis of these mortality and health metrics advances our understanding of coinfections of these two important catfish pathogens and will aid fish health diagnosticians and channel catfish producers in developing therapeutants and prevention methods to control bacterial coinfections.

Technical Abstract: Flavobacterium covae and virulent Aeromonas hydrophila are prevalent bacterial pathogens within the U.S. catfish industry that can cause high mortality in production ponds. An assessment of in vivo bacterial coinfection with virulent A. hydrophila (ML09-119) and F. covae (ALG-00-530) was conducted in juvenile channel catfish (Ictalurus punctatus). Catfish were divided into seven treatments: 1) mock control; 2 and 3) high and low doses of virulent A. hydrophila; 4 and 5) high and low doses of F. covae; 6 and 7) simultaneous challenge with high and low doses of virulent A. hydrophila and F. covae. In addition to the mortality assessment, anterior kidney and spleen were collected to evaluate immune gene expression, as well as quantify bacterial load by qPCR. At 96 h post-challenge (hpc), the high dose of virulent A. hydrophila infection (immersed in 2.3 x 10^7 CFU mL-1) resulted in cumulative percent mortality (CPM) of 28.3 ± 9.5 %, while the high dose of F. covae (immersed in 5.2 x 10^6 CFU mL-1) yielded CPM of 23.3 ± 12.9 %. When these pathogens were delivered in combination, CPM significantly increased for both the high (98.3 ± 1.36) and low dose combinations (76.7 ± 17.05 %) (P< 0.001). There were no differences in sera lysozyme activity among treatment groups; however, a significant increase (P<0.002) in lysozyme activity was observed at 12 hpc, followed by a decrease at 96 hpc (P<0.001). Three proinflammatory cytokines (tnf-alpha, il8, il1b demonstrated increased expression levels at 48 hpc. These results demonstrate the additive effects on mortality when these two pathogens are combined. The synthesis of these mortality and health metrics advances our understanding of co-infections of these two important catfish pathogens and will aid fish health diagnosticians and channel catfish producers in developing therapeutants and prevention methods to control bacterial coinfections.