Use of a Flavobacterium columnare DnaK recombinant protein vaccine to guard against columnaris disease in channel catfish

Authors: Lange, Miles

Submitted to: Proceedings of US-Japan Natural Resources Panel on Aquaculture
Publication Type: Abstract Only
Publication Acceptance Date: 10/20/2021
Publication Date: 10/28/2021
Citation: Lange, M.D. 2021. Use of a Flavobacterium columnare DnaK recombinant protein vaccine to guard against columnaris disease in channel catfish. Proceedings of US-Japan Natural Resources Panel on Aquaculture [abstract]. 13-14.

Interpretive Summary:

Technical Abstract: The incidence of different bacterial diseases and their ongoing contribution to on-farm losses including the cost of therapeutants during the production cycle persists among the U.S. catfish industry accounting for as much $17 million in overall annual lost revenue. Flavobacterium columnare causes substantial losses among cultured finfish species. The Gram-negative bacterium is an opportunistic pathogen that manifests as biofilms on the host’s mucosal surfaces as the disease progresses. We previously established that the dominant mucosal IgM antibody response to F. columnare is to the DnaK protein found in the extracellular fraction (Lange et al. 2016). Recent advances in recombinant protein technology have made the production and subsequent testing of individual immunogens quite effective. To establish the efficacy of using recombinant protein technology to develop a new vaccine against columnaris disease, we are reporting on several vaccine trials using a recombinant F. columnare DnaK protein (rDnaK). In the first study, three groups of channel catfish were immunized by bath immersion with a live attenuated F. columnare isolate, rDnaK or sham immunized. After six weeks, an F. columnare laboratory challenge showed a significant increase in survival in both the live attenuated and rDnaK vaccines when compared to the non-immunized control. A rDnaK-specific ELISA revealed significant levels of mucosal IgM antibodies present in the skin of catfish immunized with rDnaK at four- and six-weeks post immunization. In the second study, three groups of channel catfish were bath immunized with rDnaK alone or with rDnaK after a brief osmotic shock or sham immunized. In study two, after six weeks a laboratory challenge with F. columnare was conducted and showed a significant increase in survival in the rDnaK and in rDnaK with osmotic shock when compared to the non-immunized control. The rDnaK ELISA demonstrated significant levels of mucosal IgM antibodies in the skin of catfish groups immunized with rDnaK at six weeks post immunization. To further understand the processes which have conferred immune protection in the rDnaK group, we conducted RNA sequencing of skin samples from the non-immunized and rDnaK treated channel catfish at one-week and six weeks post immunization. Differential gene expression was identified between the non-immunized and immunized skin and gene ontology analyses (Lange et al. 2019). We next confirmed and extended these findings by evaluating the efficacy of the recombinant F. columnare DnaK protein vaccine when using different immersion adjuvant strategies. The results demonstrate significant protection of channel catfish at after 6 to 8 weeks post vaccination (Lange et al. 2021). Experimental methods to enhance the catfish immune response to recombinant F. columnare DnaK protein under different strategies continues as this vaccine remains a promising candidate for experimental trials in a production setting.