Interactions between salmonid serum components and the extracellular haemolytic toxin of Aeromonas salrnonicida

The interactions between salmonid serum components and the lethal extracellular haemolytic toxin (glycerophospholipid:cholesterol acyltransferase complexed with lipopolysaccharide, GCAT/LPS) of Aeromonas salmonicida were studied. Low density Lipoprotein-like (LDL-like) fractions, h ~g h density lipoprotein (HDL) and serum albumin were punfled from Atlantic salmon Salrno salar L. serum using Fast Protein Liquid Chromatographygel filtration and/or anion exchange columns. LDLlike fractions, HDL, and albumin enhanced phospholipase activities of the GCAT/LPS. Rainbow trout Oncorhynchus mykiss serum and salmon LDL-like fractions, HDL, and albumin all inhibited the haemolytic activity of the GCAT/LPS in the short term (2 h); but after 24 h incubation, both albumin and trout serum markedly enhanced this activity. In electrophoretic studies, prior incubation with the GCAT/LPS significantly increased the mobility of the LDL-like fractions, HDL, and albumin fractions. These data indicate that the interaction between the fish serum components and the GCAT/LPS results in net activation of phospholipase and haemolytic activities of the toxin and causes disturbances in the properties of the serum albumin and lipoproteins. These complex events may significantly contribute to the pathogenicity of A. salmonicida.