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(1) Characterize existing E. ictaluri-specific bacteriophages to (A) determine factors influencing host-virus infection mechanism and kinetics, (B) identify E. ictaluri membrane receptor(s) for each phage, (C) annotate the genome for each bacteriophage, and (D) identify and characterize phage lysins for E. ictaluri<P> (2) Evaluate the impact of different parameters (e.g., Ca, temperature, multiplicity of infection) on biological control of E. ictaluri pathogenesis in catfish challenge models in laboratory aquaria to prepare for challenges in aquaculture ponds. <P>(3) Sample from aquaculture ponds and other freshwater habitats to discover and characterize additional bacteriophages specific for E. ictaluri, and select for phage variants that are adapted for infection at lower temperatures, within a catfish, and/or that can infect phage-resistant E. ictaluri strains.
Non-Technical Summary: Enteric septicemia of catfish (ESC), a bacterial infection caused by Edwardsiella ictaluri, costs the catfish industry between $20 and $30 million yearly in direct fish losses. The purpose of this project is to discover naturally occurring bacteriophages that are specific for E. ictaluri, to characterize the two existing E. ictaluri-specific bacteriophages and others that are isolated, and test the use of these bacteriophages and their encoded bacteriolysins in the prevention of enteric septicemia of channel catfish. <P> Approach: Expected Results / Outcomes We anticipate that this work will result in 1) A fully characterized host range and infection kinetics for each bacteriophage, 2) Complete bacteriophage genome sequence (estimated at ~45kb in size for each) for the two bacteriophages already discovered, 3) Identification of E. ictaluri lysins encoded by the bacteriophages and assessment of their ability to lyse E. ictaluri in the laboratory and in aquarium challenges, 4) Identification of key variables to be considered for effectiveness of phage biocontrol of ESC in aquarium and pond infections, and 5) A collection of novel bacteriophages lytic for E. ictaluri. The phages discovered will be useful not only in terms of ESC biocontrol, but also in E. ictaluri diagnostic tests and research efforts by other groups studying ESC disease.