Cell surface of the fish pathogenic bacterium Aeromonas salmonicida: I. Relationship between autoagglutination and the presence of a major cell envelope protein

A comparison was made of membrane protein patterns of various Aeromonas salmonicida strains, initially isolated from different habitats with respect to fish species affected, pathological entity, and geographic location of the outbreak of the disease. A major protein with a molecular weight of 54 000 was found in all autoagglutinating strains, whereas this protein is present in low amounts, or not at all, in non-autoagglutinating strains. Evidence for a causal relationship between the presence of this protein and the phenomenon of autoagglutination came from the observation that a change of the growth medium led simultaneously to an almost complete loss of the additional cell envelope protein and the property of autoagglutination. As it has already been reported that autoagglutination is correlated with the presence of an additional cell surface layer, we hypothesize that the additional cell envelope protein is the (major) subunit of this layer. The application of the gel immuno radio assay, an immunological technique suited to detect antigens in a gel, revealed that the additional cell envelope proteins of all tested strains are immunologically related. The possibility to the use of this protein as a component of a vaccine against A. salmonicida infections is discussed.