Antibody responses of rainbow trout (Oncorhynchus mykiss, Walbaum) to liveAeromonas hydrophilaas assessed by various antigen preparations

Sera from rainbow trout (Oncorhynchus mykiss, Walbaum), which had been immunised with live cells ofAeromonas hydrophila, caused strong agglutination of formalised and live cells ofA. hydrophila. In contrast, lower titres were recorded with sheared and pasteurised cells. Extremely weak agglutination occurred with boiled or lipopolysaccharide (LPS) deficient cells. By means of enzyme linked immunosorbent assays (ELISA), it was revealed that trout antiserum reacted with LPS, extracellular products (ECP), exopolysaccharides (EPS), and subcellular components derived from cells which had been pasteurised, sheared, boiled or extracted with EDTA and/or guanidine. It was concluded that LPS is the major antigenic component of whole cells, whereas EPS and a haemolytic component of the ECP could have induced an antibody response in the fish.