Protective immunity against enteric septicaemia in channel catfish, Ictalurus punctatus (Rafinesque), following controlled exposure to Edwardsiella ictaluri

Protective immunity against enteric septicaemia of catfish (ESC) following immunization with Edwardsiella ictaluri bacterins and exposure to live E. ictaluri was investigated. Mean cumulative percentage survival was significantly higher (P less than or equal to 0.05) in controlled live vaccinates (100%) than in immersion and oral bacterin vaccinates (68.3% and 50.0%, respectively). Bactericidal activity against E. ictaluri by peritoneal macrophages from controlled live vaccinates (85.9%) was significantly greater (P less than or equal to 0.05) than bactericidal activity of macrophages from immersion bacterin vaccinates (71.4%) or non-vaccinates (68.1%). No significant (P > 0.05) difference was found in the bactericidal activity of macrophages from oral bacterin vaccinates and macrophages from controlled live vaccinates. The E. ictaluri-specific antibody response of controlled li ie (0.08 OD) and immersion bacterin vaccinates (0.11 OD) was significantly higher (P less than or equal to 0.05) than that of oral bacterin vaccinates and non-vaccinates (0.01 OD) 15 days post-vaccination. A significantly higher antibody response was seen in controlled live vaccinates (0.17 OD), when compared re other vaccinates or non-vaccinates 33 days after vaccination. Neither immersion nor oral bacterins protected the vaccinates against ESC. Controlled live E. ictaluri immunization of channel catfish resulted in production of specific antibodies, increased macrophage bactericidal activity and protection against ESC.