Enhancement of bacterial adhesion by shear forces: characterization of the haemagglutination induced by Aeromonas salmonicida strain 438.

Application of a viscometric assay to the haemagglutination induced by Aeromonas salmonicida strain 438 showed that shear forces can enhance the strength of bacterial adhesion. The D-mannose/L-fucose-sensitive reaction proceeded in two phases, an initial phase in which the degree of aggregation remained constant during shearing and a second stage, induced by shear, in which agglutination was enhanced as shear was maintained. The results strongly paralleled those found in studies of concanavalin A-induced haemagglutination, providing good evidence that adhesion in this species took place via lectin-like molecules. Methyl-alpha-D-mannoside, which strongly inhibits haemagglutination in this system, would not fully reverse the shear-dependent reaction. EGTA inhibited and reversed both phases, however. The effects of bacterial concentration, temperature, time of growth, pH, and a spectrum of monosaccharide inhibitors were also studied. The results demonstrated that the shear-dependent reaction has a number of features which distinguish it from the initial stage of haemagglutination, implying differences in the underlying biochemical mechanisms involved.