176
to fi sh cells but contribute more signifi cantly to cell invasion (Merino et al. 1997 ).
A group II capsule gene cluster has been recognized, and the purifi ed polysaccharide increased the ability of an avirulent culture to survive in (tilapia) serum and
phagocytosis (Zhang et al. 2003 ). With attachment, the host cell will be at the mercy
of the pathogen. Although the precise mechanism of cell damage and tissue damage
remains unproven, the available evidence points to the involvement of both endoand exo-toxins. Experiments with fi sh epidermal cells revealed that Aer. hydrophila
could survive internally (Tan et al. 1998 ). Here, a role for tyrosine phosphorylation
in the internalisation process was suggested (Tan et al. 1998 ). Indeed, subsequent
work documented the ability of Aer. hydrophila to be internalized and survive in
macrophages of eel ( Anguilla japonica ) with the mode of action refl ecting the presence of fl agella and thus motility (Qin et al. 2014 ).
Outer Membrane Proteins (OMPs)
Differences in the OMP according to incubation temperature has been documented,
with a 40 kDa band produced following incubation at 17 and 25 °C, which also
coincided with the greatest virulence and least phagocytic activity by goldfi sh macrophages (Rahman et al. 2001 ).
Extracellular Products (ECPs)
In comparison with Aer. salmonicida, fi sh pathogenic strains of Aer. hydrophila
produce ECP, which contains considerable enzymatic activity (Shotts et al. 1984 ;
Santos et al. 1987 ), including haemolysins and proteases (Angka et al. 1995 ; Khalil
and Mansour 1997 ), and in particular a 64 kDa serine protease (Cascón et al. 2000 )
with optimum production [of protease] at 27.6 +/− 4.9 °C (Uddin et al. 1997 ).
Interestingly, the highest mortalities were reported to occur in goldfi sh at 17 and
25 °C (compared to 10 and 32 °C) (Rahman et al. 2001 ). The relevance of the ECP
was highlighted by Allan and Stevenson ( 1981 ) and Stevenson and Allan ( 1981 ),
who succeeded in causing a pathology in fi sh as a result of injection of the material.
Yet, the role of ECP is debatable with contrasting views of the importance of ‘haemolysins’ in virulence (Thune et al. 1986 ; Toranzo et al. 1989 ; Karunasagar et al.
1990 ; Paniagua et al. 1990 ). Stevenson and colleagues reported haemolytic (heatlabile) and proteolytic activity, the former of which was concluded to be of greater
importance in pathogenesis. Kanai and Takagi ( 1986 ) recovered an a-type haemolysin which was deemed to be heat-stable and stable at pH 4–1.2, but inactivated by
EDTA, trypsin and papain. The crude preparation caused swelling and reddening of
the body surface following injection into carp. Previously, Boulanger et al. ( 1977 )
isolated two types of haemolysins. The reasons then for the conclusion about the
4 Aeromonadaceae Representatives (Motile Aeromonads)
to fi sh cells but contribute more signifi cantly to cell invasion (Merino et al. 1997 ).
A group II capsule gene cluster has been recognized, and the purifi ed polysaccharide increased the ability of an avirulent culture to survive in (tilapia) serum and
phagocytosis (Zhang et al. 2003 ). With attachment, the host cell will be at the mercy
of the pathogen. Although the precise mechanism of cell damage and tissue damage
remains unproven, the available evidence points to the involvement of both endoand exo-toxins. Experiments with fi sh epidermal cells revealed that Aer. hydrophila
could survive internally (Tan et al. 1998 ). Here, a role for tyrosine phosphorylation
in the internalisation process was suggested (Tan et al. 1998 ). Indeed, subsequent
work documented the ability of Aer. hydrophila to be internalized and survive in
macrophages of eel ( Anguilla japonica ) with the mode of action refl ecting the presence of fl agella and thus motility (Qin et al. 2014 ).
Outer Membrane Proteins (OMPs)
Differences in the OMP according to incubation temperature has been documented,
with a 40 kDa band produced following incubation at 17 and 25 °C, which also
coincided with the greatest virulence and least phagocytic activity by goldfi sh macrophages (Rahman et al. 2001 ).
Extracellular Products (ECPs)
In comparison with Aer. salmonicida, fi sh pathogenic strains of Aer. hydrophila
produce ECP, which contains considerable enzymatic activity (Shotts et al. 1984 ;
Santos et al. 1987 ), including haemolysins and proteases (Angka et al. 1995 ; Khalil
and Mansour 1997 ), and in particular a 64 kDa serine protease (Cascón et al. 2000 )
with optimum production [of protease] at 27.6 +/− 4.9 °C (Uddin et al. 1997 ).
Interestingly, the highest mortalities were reported to occur in goldfi sh at 17 and
25 °C (compared to 10 and 32 °C) (Rahman et al. 2001 ). The relevance of the ECP
was highlighted by Allan and Stevenson ( 1981 ) and Stevenson and Allan ( 1981 ),
who succeeded in causing a pathology in fi sh as a result of injection of the material.
Yet, the role of ECP is debatable with contrasting views of the importance of ‘haemolysins’ in virulence (Thune et al. 1986 ; Toranzo et al. 1989 ; Karunasagar et al.
1990 ; Paniagua et al. 1990 ). Stevenson and colleagues reported haemolytic (heatlabile) and proteolytic activity, the former of which was concluded to be of greater
importance in pathogenesis. Kanai and Takagi ( 1986 ) recovered an a-type haemolysin which was deemed to be heat-stable and stable at pH 4–1.2, but inactivated by
EDTA, trypsin and papain. The crude preparation caused swelling and reddening of
the body surface following injection into carp. Previously, Boulanger et al. ( 1977 )
isolated two types of haemolysins. The reasons then for the conclusion about the
4 Aeromonadaceae Representatives (Motile Aeromonads)