An orally delivered, live-attenuated Edwardsiella ictaluri vaccine efficiently protects channel catfish fingerlings against multiple Edwardsiella ictaluri field isolates

Authors: AARATTUTHODIYIL, SUJA - Mississippi State University; GRIFFIN, MATT - Mississippi State University; GREENWAY, TERRENCE - Mississippi State University; KHOO, LESTER - Mississippi State University; BYARS, TODD - Mississippi State University; LEWIS, MARSHA - Mississippi State University; STEADMAN, JAMES - Mississippi State University; WISE, DAVID - Mississippi State University

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2020
Publication Date: 4/30/2020
Citation: Aarattuthodiyil, S., Griffin, M.J., Greenway, T.E., Khoo, L.H., Byars, T.S., Lewis, M., Steadman, J., Wise, D.J. 2020. An orally delivered, live-attenuated Edwardsiella ictaluri vaccine efficiently protects channel catfish fingerlings against multiple Edwardsiella ictaluri field isolates. Journal of the World Aquaculture Society. 51(6)1354-1372. https://doi.org/10.1111/jwas.12693.
DOI: https://doi.org/10.1111/jwas.12693

Interpretive Summary: Enteric septicemia of catfish (ESC), caused by Edwardsiella ictaluri, remains a major challenge for the commercial Channel Catfish industry, leading to significant losses. To improve disease management, researchers investigated the effectiveness of a live-attenuated E. ictaluri oral vaccine over a three-year period. The vaccine was tested against a diverse set of archived E. ictaluri isolates collected from catfish farms in Mississippi and Alabama between 1993 and 2016, including samples from both vaccinated and nonvaccinated populations.Molecular analysis revealed that E. ictaluri populations in catfish aquaculture have remained genetically stable over time, despite the presence of at least four distinct plasmid types. Importantly, the vaccine provided protection against all tested isolates, regardless of their genetic or plasmid differences. Furthermore, antimicrobial sensitivity testing confirmed that the vaccine strain does not carry multidrug resistance genes.These findings suggest that a multivalent vaccine, designed to target multiple strains, may not be necessary, as the current E. ictaluri vaccine is broadly protective. This research provides valuable insight into vaccine efficacy and supports the continued use of this oral vaccination strategy to control ESC in farm-raised catfish.

Technical Abstract: The commercial channel catfish (Ictalurus punctatus) industry is adversely impacted by enteric septicemia of catfish (ESC), caused by the Gram-negative enteric rod Edwardsiella ictaluri. In efforts to develop more effective management strategies, the use of a live-attenuated E. ictaluri isolate as an oral vaccine was investigated. The utility and broad application of a vaccine is dependent on the protection offered against multiple field isolates. Immunization trials, followed by bacterial challenge with archived virulent E. ictaluri isolates from the catfish farming region of the southeastern United States, were conducted over a 3-year period. These isolates were archived from 1993 to 2016 and included representatives from nonvaccinated and vaccinated populations of diseased channel catfish in Mississippi, an isolate from nonvaccinated hybrid catfish raised in Mississippi, and an isolate from nonvaccinated channel catfish from Alabama. Molecular characterization of the isolates revealed a high degree of genetic similarity evidenced by repetitive sequence-mediated polymerase chain reaction (rep-PCR) fingerprinting and virulence gene amplification, suggesting that the population of E. ictaluri within catfish aquaculture in Mississippi and Alabama has been genetically stable over time. Plasmid profiling revealed the existence of at least four distinct plasmids among field isolates. Nevertheless, the E. ictaluri vaccine protected fish against all isolates, irrespective of heterogeneous or homogeneous plasmid profiles. In addition, plasmid profiles were supported by antimicrobial sensitivity testing, indicating that the E. ictaluri vaccine strain does not carry natural or plasmid-mediated multidrug resistance to the three antibiotics approved for use in U.S. food fish aquaculture. Challenge data from this study argue against the need for multivalent E. ictaluri vaccines to account for presumed antigenic or genetic variation among wild-type E. ictaluri isolates as the vaccine was effective against all archived isolates.