The Infection Dynamics of Experimental Edwardsiella ictaluri and Flavobacterium covae Coinfection in Channel Catfish (Ictalurus punctatus)

Authors: WISE, ALLISON - Auburn University; LAFRENTZ, BENJAMIN - USDA-ARS Sino-american Biological Control Laboratory; KELLY, ANITA - Auburn University; LILES, MARK - Auburn University; GRIFFIN, MATT - Mississippi State University; BECK, BENJAMIN - USDA-ARS Sino-american Biological Control Laboratory; BRUCE, TIMOTHY - Auburn University

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2023
Publication Date: 3/15/2023
Citation: Wise, A.L., Lafrentz, B.R., Kely, A.M., Liles, M.R., Griffin, M.J., Beck, B.H., Bruce, T.J. 2023. The Infection Dynamics of Experimental Edwardsiella ictaluri and Flavobacterium covae Coinfection in Channel Catfish (Ictalurus punctatus). Pathogens. 12(3)462. https://doi.org/10.3390/pathogens12030462.
DOI: https://doi.org/10.3390/pathogens12030462

Interpretive Summary: This study examines the impact of Edwardsiella ictaluri and Flavobacterium covae coinfections in channel catfish, demonstrating that E. ictaluri largely drives mortality outcomes, regardless of infection order. However, prior exposure to F. covae delayed peak mortality, suggesting potential interactions between these pathogens. These findings improve our understanding of bacterial coinfection dynamics in catfish aquaculture, helping inform targeted disease management strategies to mitigate losses.

Technical Abstract: Edwardsiella ictaluri and Flavobacterium covae are pervasive bacterial pathogens associated with significant losses in catfish aquaculture. Bacterial coinfections have the potential to increase outbreak severity and can worsen on-farm mortality. A preliminary assessment of in vivo bacterial coinfection with E. ictaluri (S97-773) and F. covae (ALG-00-530) was conducted using juvenile channel catfish (Ictalurus punctatus). Catfish were divided into five treatment groups: (1) mock control; (2) E. ictaluri full dose (immersion; 5.4 × 10e5 CFU mL-1); (3) F. covae full dose (immersion; 3.6 × 10e6 CFU mL-1); (4) E. ictaluri half dose (immersion; 2.7 × 10e5 CFU mL-1) followed by half dose F. covae (immersion; 1.8 × 10e6 CFU mL-1); and (5) F. covae half dose followed by half dose E. ictaluri. In the coinfection challenges, the second inoculum was delivered 48 h after the initial exposure. At 21 days post-challenge (DPC), the single dose E. ictaluri infection yielded a cumulative percent mortality (CPM) of 90.0 ± 4.1%, compared with 13.3 ± 5.9% in the F. covae group. Mortality patterns in coinfection challenges mimicked the single dose E. ictaluri challenge, with CPM of 93.3 ± 5.4% for fish initially challenged with E. ictaluri followed by F. covae, and 93.3 ± 2.7% for fish exposed to F. covae and subsequently challenged with E. ictaluri. Despite similarities in the final CPM within the coinfection groups, the onset of peak mortality was delayed in fish exposed to F. covae first but was congruent with mortality trends in the E. ictaluri challenge. Catfish exposed to E. ictaluri in both the single and coinfected treatments displayed increased serum lysozyme activity at 4-DPC (p < 0.001). Three pro-inflammatory cytokines (il8, tnfa, il1ß) were evaluated for gene expression, revealing an increase in expression at 7-DPC in all E. ictaluri exposed treatments (p < 0.05). These data enhance our understanding of the dynamics of E. ictaluri and F. covae coinfections in US farm-raised catfish.