Evaluation of Edwardsiella piscicida basS and basR mutants as vaccine candidates in catfish against edwardsiellosis

Authors: SAYED, MOHAMED - Mississippi State University; GRIFFIN, MATT - Mississippi State University; WARE, CYNTHIA - Mississippi State University; OZDEMIR, OZAN - Mississippi State University; TEKEDAR, HASAN - Mississippi State University; ESSA, MANAL - Beni Suef University - Egypt; KARSI, ATTILA - Mississippi State University; LAWRENCE, MARK - Mississippi State University; ABDELHAMED, HOSSAM - Mississippi State University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2022
Publication Date: 8/21/2022
Citation: Sayed, M., Griffin, M., Ware, C., Ozdemir, O., Tekedar, H.C., Essa, M., Karsi, A., Lawrence, M.L., Abdelhamed, H. 2022. Evaluation of Edwardsiella piscicida basS and basR mutants as vaccine candidates in catfish against edwardsiellosis. Journal of Fish Diseases. 45(12)1817-1829. https://doi.org/10.1111/jfd.13703.
DOI: https://doi.org/10.1111/jfd.13703

Interpretive Summary: Two mutant strains of E. piscicida were constructed through gene deletion and assessed for virulence and potential as vaccines in channel catfish. The results revealed that both mutants exhibited increased sensitivity to acidic environments and produced significantly less biofilm compared to the wild-type strain. In catfish infection trials, both mutants showed decreased virulence and offered long term protection against virulent E. piscicida strains. In summary, this research offers valuable insights into the virulence mechanisms of E. piscicida and highlights the potential use of gene deleted mutants as a safe and protective vaccine for combating E. piscicida infections in catfish farming.

Technical Abstract: Catfish farming is the largest aquaculture industry in the United States and an important economic driver in several southeastern states. Edwardsiella piscicida is a Gram-negative pathogen associated with significant losses in catfish aquaculture. Several Gram-negative bacteria use the BasS/BasR two-component system (TCS) to adapt to environmental changes and the host immune system. Currently, the role of BasS/BasR system in E. piscicida virulence has not been characterized. In the present study, two mutants were constructed by deleting the basS and basR genes in E. piscicida strain C07-087. Both mutant strains were characterized for virulence and immune protection in catfish hosts. The Ep'basS and Ep'basR mutants were more sensitive to acidic environments and produced significantly less biofilm than the wild-type. In vivo studies in channel catfish (Ictalurus punctatus) revealed that both Ep'basS and Ep'basR were significantly attenuated compared with the parental wild-type (3.57% and 4.17% vs. 49.16% mortalities). Moreover, there was significant protection, 95.2% and 92.3% relative percent survival (RPS), in channel catfish vaccinated with Ep'basS and Ep'basR against E. piscicida infection. Protection in channel catfish was associated with a significantly higher level of antibodies and upregulation of immune-related genes (IgM, IL-8 and CD8-a) in channel catfish vaccinated with Ep'basS and Ep'basR strains compared with non-vaccinated fish. Hybrid catfish (channel catfish ''×'blue catfish ') challenges demonstrated long-term protection against subsequent challenges with E. piscicida and E. ictaluri. Our findings demonstrate BasS and BasR contribute to acid tolerance and biofilm formation, which may facilitate E. piscicida survival in harsh environments. Further, our results show that Ep'basS and Ep'basR mutants were safe and protective in channel catfish fingerlings, although their virulence and efficacy in hybrid catfish warrant further investigation. These data provide information regarding an important mechanism of E. piscicida virulence, and it suggests Ep'basS and Ep'basR strains have potential as vaccines against this emergent catfish pathogen.