175
1988 ). Nevertheless in Aer. salmonicida, the S-layer has indeed been shown to be a
pre-requisite for virulence, by increasing hydrophobicity and enhancing macrophage association (Murray et al. 1988 ).
The detailed structure of the S-layer has been revealed in an excellent series of
publications (Dooley et al. 1986 , 1988 ; Dooley and Trust 1988 ). After studying 8
isolates of a serogroup with a high virulence to fi sh, Dooley and Trust ( 1988 ) concluded that the S-layer was tetragonally arrayed. SDS-PAGE revealed a protein of
52 kDa molecular weight, which was the major surface (protein) antigen. This protein effectively masked the underlying OMP.
Ascencio et al. ( 1991 ) investigated extracellular matrix protein binding to Aer
hydrophila. In particular, binding of
125 I-labelled collagen, fi bronectin and laminin
is common to isolates from diseased fi sh. Moreover, the binding property was specifi c, with cultural conditions infl uencing expression of the bacterial cell surface
binding structures. Experiments showed that calcium (in the growth medium)
enhanced expression of the bacterial extracellular matrix protein surface receptors.
The conclusion was reached that success in infecting/colonising a host depended on
the ability of the pathogen to bind to specifi c cell surface receptors of the mucus
layer, epithelial cells and subepithelial basement membranes.
“Adhesins”
The pathogen displays chemotaxis towards [gut] mucus, and adherence to and
growth in the mucus (van der Marel et al. 2008 ). It appears that the pathogen has the
ability to attach to selected host cells, e.g. erythrocytes, and tissue proteins, i.e. collagen, fi bronectin, serum proteins and glycoproteins, via the action of ‘adhesins’
(Trust et al. 1980a , b , c ; Toranzo et al. 1989 ; Ascencio et al. 1991 ; Lee et al. 1997 ;
Fang et al. 2004 ) and become internalised (Tan et al. 1998 ). The adhesins, of which
a 43 kDa (AHA1) adhesin has been cloned and shown to have high homology to two
OMPs (Fang et al. 2004 ), appear to be extremely selective, recognising D-mannose
and L-fucose side chains on polymers located on the surface of the eukaryotic cells.
The specifi city was further highlighted by the observation that human isolates of
Aer. hydrophila failed to bind (or bound poorly) to fi sh tissue culture cells (Krovacek
et al. 1987 ). Indeed using tissue culture cells from rainbow trout liver and chinook
salmon embryo, Krovacek et al. ( 1987 ) demonstrated that some (~33 %) isolates of
Aer. hydrophila from fi sh adhered to the tissue culture cells and glass surfaces
coated with rainbow trout mucus. Adhesion and adsorption were time dependent;
and the activities were lost after treatment of the bacteria with heat, proteolytic
enzymes or ultra-sound.
Invasion of Fish Cells
The 43 kDa protein has been regarded as important for the invasion of epithelial
cells, in vitro (Lee et al. 1997 ; Fang et al. 2004 ). Other workers have pointed to the
relevance of capsular polysaccharides, which appear to enhance slightly adherence
Aeromonas hydrophila
1988 ). Nevertheless in Aer. salmonicida, the S-layer has indeed been shown to be a
pre-requisite for virulence, by increasing hydrophobicity and enhancing macrophage association (Murray et al. 1988 ).
The detailed structure of the S-layer has been revealed in an excellent series of
publications (Dooley et al. 1986 , 1988 ; Dooley and Trust 1988 ). After studying 8
isolates of a serogroup with a high virulence to fi sh, Dooley and Trust ( 1988 ) concluded that the S-layer was tetragonally arrayed. SDS-PAGE revealed a protein of
52 kDa molecular weight, which was the major surface (protein) antigen. This protein effectively masked the underlying OMP.
Ascencio et al. ( 1991 ) investigated extracellular matrix protein binding to Aer
hydrophila. In particular, binding of
125 I-labelled collagen, fi bronectin and laminin
is common to isolates from diseased fi sh. Moreover, the binding property was specifi c, with cultural conditions infl uencing expression of the bacterial cell surface
binding structures. Experiments showed that calcium (in the growth medium)
enhanced expression of the bacterial extracellular matrix protein surface receptors.
The conclusion was reached that success in infecting/colonising a host depended on
the ability of the pathogen to bind to specifi c cell surface receptors of the mucus
layer, epithelial cells and subepithelial basement membranes.
“Adhesins”
The pathogen displays chemotaxis towards [gut] mucus, and adherence to and
growth in the mucus (van der Marel et al. 2008 ). It appears that the pathogen has the
ability to attach to selected host cells, e.g. erythrocytes, and tissue proteins, i.e. collagen, fi bronectin, serum proteins and glycoproteins, via the action of ‘adhesins’
(Trust et al. 1980a , b , c ; Toranzo et al. 1989 ; Ascencio et al. 1991 ; Lee et al. 1997 ;
Fang et al. 2004 ) and become internalised (Tan et al. 1998 ). The adhesins, of which
a 43 kDa (AHA1) adhesin has been cloned and shown to have high homology to two
OMPs (Fang et al. 2004 ), appear to be extremely selective, recognising D-mannose
and L-fucose side chains on polymers located on the surface of the eukaryotic cells.
The specifi city was further highlighted by the observation that human isolates of
Aer. hydrophila failed to bind (or bound poorly) to fi sh tissue culture cells (Krovacek
et al. 1987 ). Indeed using tissue culture cells from rainbow trout liver and chinook
salmon embryo, Krovacek et al. ( 1987 ) demonstrated that some (~33 %) isolates of
Aer. hydrophila from fi sh adhered to the tissue culture cells and glass surfaces
coated with rainbow trout mucus. Adhesion and adsorption were time dependent;
and the activities were lost after treatment of the bacteria with heat, proteolytic
enzymes or ultra-sound.
Invasion of Fish Cells
The 43 kDa protein has been regarded as important for the invasion of epithelial
cells, in vitro (Lee et al. 1997 ; Fang et al. 2004 ). Other workers have pointed to the
relevance of capsular polysaccharides, which appear to enhance slightly adherence
Aeromonas hydrophila