Protection against enteric septicemia of catfish (Ictalurus punctatus) by immunization with the R-mutant, Escherichia coli (J5).

The protective effects of immunization with the rough (R) mutant, Escherichia coli (J5), were evaluated in an experimental model of Edwardsiella ictaluri-induced enteric septicemia of catfish (Ictalurus punctatus). Groups of 18 to 25 fish were administered killed E coli (J5) with or without an aluminum hydroxide (alum) adjuvant by intraperitoneal (i.p.) or IM route. Vaccinated fish were experimentally infected with virulent Ed ictaluri. Fish were monitored to determine survival after Ed ictaluri infection. Fish that received E coli (J5) in alum i.p. had enhanced survival (92%), compared with fish given E coli (J5) i.p. only (54%, P < 0.05) or fish given saline solution i.p. (56%, P < 0.05). Fish given E coli (J5) in alum i.m. had intermediate survival (77%), which did not differ significantly (P > 0.05) from survival of fish in the other 3 vaccination groups. Serologic responses to Ed ictaluri and E coli (J5) before and after immunization with E coli (J5) were determined, using whole-cell ELISA. Serologic recognition of both whole cell antigens increased significantly (P < 0.10) in all groups; however, the most pronounced increase was observed in fish that received E coli (J5) in alum i.p.. These results indicate the i.p. administration of E coli (J5) in alum protects against enteric septicemia of catfish.