Abstract
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 demonstrated that the dominant mucosal IgM antibody response to F. columnare is to the chaperone protein DnaK that is found in the extracellular fraction. To establish the efficacy of using recombinant protein technology to develop a new vaccine against columnaris disease, we are reporting on two consecutive years of vaccine trials using a recombinant F. columnare DnaK protein (rDnaK). In year one, three groups of channel catfish (n = 300) were immunized by bath immersion with a live attenuated F. columnare isolate, rDnaK or sham immunized. After 6 weeks, an F. columnare laboratory challenge showed a significant increase in survival (>30%) 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 in the skin of catfish immunized with rDnaK at 4- and 6-weeks post immunization. In the second year, three groups of channel catfish (n = 300) were bath immunized with rDnaK alone or with rDnaK after a brief osmotic shock or sham immunized. After 6 weeks a laboratory challenge with F. columnare was conducted and showed a significant increase in survival in the rDnaK (> 25%) and in rDnaK with osmotic shock (>35%) groups when compared to the non-immunized control. The rDnaK-specific ELISA demonstrated significant levels of mucosal IgM antibodies in the skin of catfish groups immunized with rDnaK at 4- and 6-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 (n = 6) and rDnaK treated channel catfish at 1-week (n = 6) and 6 weeks (n = 6) post immunization. Significantly altered gene expression was identified and results will be discussed. Work to further enhance the catfish immune response to F. columnare rDnaK is underway as this protein remains a promising candidate for additional optimization and experimental trials in a production setting.
Highlights
Flavobacterium columnare, the causative agent of columnaris disease generates substantial mortality during the production of freshwater farmed finfish species [1, 2]
An alignment of DnaK amino acid sequences from recently released F. columnare genomes and protein sequences from other Gram-negative bacteria were compared to that identified in F. columnare ATCC 49512 (Table S1)
Columnaris disease continues to be a significant issue among the different production systems of warmwater finfish
Summary
Flavobacterium columnare, the causative agent of columnaris disease generates substantial mortality during the production of freshwater farmed finfish species [1, 2]. Columnaris disease has been shown to predominantly involve the external mucosal surfaces of fish, which can lead to the rapid and widespread destruction of the gills, skin, and fins. Intensive rearing of food fish is well-suited for the transmission of F. columnare and in these settings the pathogen is opportunistic and outbreaks are common, as fish experience stressors including increased rearing density, unnecessary handling and poor water quality [5,6,7]. As food fish production continues to expand, the frequency of columnaris disease will only continue to increase within the aquaculture industry. The regulation of treatments and resistance to available antibiotics means that alternative methods of disease protection will be required [8]
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