Tissue persistence and vaccine efficacy of tricarboxylic acid cycle and one-carbon metabolism mutant strains of Edwardsiella ictaluri.

Abstract

Edwardsiella ictaluri causes enteric septicemia in fish. Recently, we reported construction of E. ictaluri mutants with single and double gene deletions in tricarboxylic acid cycle (TCA) and one-carbon (C-1) metabolism. Here, we report the tissue persistence, virulence, and vaccine efficacy of TCA cycle (Ei&#x394;sdhC, Ei&#x394;frdA, and Ei&#x394;mdh), C-1 metabolism (Ei&#x394;gcvP and Ei&#x394;glyA), and combination mutants (Ei&#x394;frdA&#x394;sdhC, Ei&#x394;gcvP&#x394;sdhC, Ei&#x394;mdh&#x394;sdhC, and Ei&#x394;gcvP&#x394;glyA) in channel catfish. The tissue persistence study showed that Ei&#x394;sdhC, Ei&#x394;frdA, Ei&#x394;frdA&#x394;sdhC, and Ei&#x394;gcvP&#x394;sdhC were able to invade catfish and persist until 11 days post-infection. Vaccination of catfish fingerlings with all nine mutants provided significant (P<0.05) protection against subsequent challenge with the virulent parental strain. Vaccinated catfish fingerlings had 100% survival when subsequently challenged by immersion with wild-type E. ictaluri except for Ei&#x394;gcvP&#x394;glyA and Ei&#x394;gcvP. Mutant Ei&#x394;gcvP&#x394;sdhC was found to be very good at protecting catfish fry, as evidenced by 10-fold higher survival compared to non-vaccinated fish.