271
Agglutination of Fish Cells
Another cell-associated factor, possibly relevant to virulence of Aer. salmonicida, is
the ability of the pathogen to agglutinate trout and mammalian erythrocytes
(Mellergaard and Larsen 1981 ). The haemagglutination capability is proported to be
related to the presence of adhesins, which are structures on the bacterial surface that
mediate the attachment of the pathogen to the host’s cell surface. Thus, the interest
in haemagglutination is due primarily to its use to provide semi-quantitative information on the adhesive potential of a bacterial strain, while the sugar inhibition of
haemagglutination has allowed adhesive specifi city to be demonstrated (Duguid
and Old 1980 ). There is good agreement in the literature on the haemagglutinating
ability of Aer. salmonicida. For instance, Jiwa ( 1983 ) reported mannose-resistant
agglutination of bovine, chicken, human group A and guinea-pig erythrocytes by
two Aer. salmonicida isolates which were recovered from diseased brown trout. It
has also been demonstrated that smooth strains were unable to agglutinate erythrocytes, whereas rough strains showed a broad spectrum of haemagglutinating activity. Similarly, Parker and Munn ( 1985 ) observed that virulent, auto-agglutinating
A-layer
+ cells agglutinated trout erythrocytes as well as a range of mammalian
erythrocytes. They also noted that the process was not inhibited by specifi c sugars,
and thus concluded that adhesion was a relatively non-specifi c process, attributable
to the hydrophobic properties of the A-layer.
Extracellular Products
Researchers interested in the biology of Aer. salmonicida have been aware for some
time that extracellular substances (produced by the organism) presumably exerted a
role in virulence. However, ECPs are not always harmful to fi sh. For example,
Madetoja et al. ( 2003 ) reported that ECPs, which lacked caseinase and gelatinase
and had low cytotoxic activity in cell culture, from an atypical strain isolated from
Arctic charr did not cause mortalities. Nevertheless, the ECP have been the focus of
numerous investigations. Unfortunately, the work has been rendered more diffi cult
by the complexity of the substance(s), which, at present, is known to include an
ADP-ribosyltransferase toxin (AexT) (Braun et al. 2002 ), acetylcholinesterase (an
ichthyotoxin with neurotoxic activity; Pérez et al. 1998 ), several proteases namely
two metalloproteases, i.e. the 37 kDa leucine aminopeptidase and the 30 kDa metalloprotease 3 (Arnesen and Eggset 1999 ), P1, GCAT, metalloendopeptidase AsaP1,
P2 metallo-gelatinase and a serine caseinase (Gudmundsdóttir and Gudmundsdóttir
1997 ; Schwenteit et al. 2015 ), phospholipase, haemolysins and a leucocidin (Munro
et al. 1980 ; Sheeran and Smith 1981 ; Shieh and MacLean 1975 ; Titball and Munn
1981 ; Cipriano et al. 1981 ; Fuller et al. 1977 ; Rockey et al. 1988 ; Huntly et al. 1992 ;
Lygren et al. 1998 ), as well as LPS. Work with monoclonal antibodies has shown
heterogeneity in the LPS (Rockey et al. 1991 ). Ellis et al. ( 1981 ) reported that ECP
of the pathogen, prepared by a cellophane overlay method, reproduced the lesions
normally associated with the chronic form of furunculosis, e.g. muscle necrosis and
Aeromonas salmonicida
Agglutination of Fish Cells
Another cell-associated factor, possibly relevant to virulence of Aer. salmonicida, is
the ability of the pathogen to agglutinate trout and mammalian erythrocytes
(Mellergaard and Larsen 1981 ). The haemagglutination capability is proported to be
related to the presence of adhesins, which are structures on the bacterial surface that
mediate the attachment of the pathogen to the host’s cell surface. Thus, the interest
in haemagglutination is due primarily to its use to provide semi-quantitative information on the adhesive potential of a bacterial strain, while the sugar inhibition of
haemagglutination has allowed adhesive specifi city to be demonstrated (Duguid
and Old 1980 ). There is good agreement in the literature on the haemagglutinating
ability of Aer. salmonicida. For instance, Jiwa ( 1983 ) reported mannose-resistant
agglutination of bovine, chicken, human group A and guinea-pig erythrocytes by
two Aer. salmonicida isolates which were recovered from diseased brown trout. It
has also been demonstrated that smooth strains were unable to agglutinate erythrocytes, whereas rough strains showed a broad spectrum of haemagglutinating activity. Similarly, Parker and Munn ( 1985 ) observed that virulent, auto-agglutinating
A-layer
+ cells agglutinated trout erythrocytes as well as a range of mammalian
erythrocytes. They also noted that the process was not inhibited by specifi c sugars,
and thus concluded that adhesion was a relatively non-specifi c process, attributable
to the hydrophobic properties of the A-layer.
Extracellular Products
Researchers interested in the biology of Aer. salmonicida have been aware for some
time that extracellular substances (produced by the organism) presumably exerted a
role in virulence. However, ECPs are not always harmful to fi sh. For example,
Madetoja et al. ( 2003 ) reported that ECPs, which lacked caseinase and gelatinase
and had low cytotoxic activity in cell culture, from an atypical strain isolated from
Arctic charr did not cause mortalities. Nevertheless, the ECP have been the focus of
numerous investigations. Unfortunately, the work has been rendered more diffi cult
by the complexity of the substance(s), which, at present, is known to include an
ADP-ribosyltransferase toxin (AexT) (Braun et al. 2002 ), acetylcholinesterase (an
ichthyotoxin with neurotoxic activity; Pérez et al. 1998 ), several proteases namely
two metalloproteases, i.e. the 37 kDa leucine aminopeptidase and the 30 kDa metalloprotease 3 (Arnesen and Eggset 1999 ), P1, GCAT, metalloendopeptidase AsaP1,
P2 metallo-gelatinase and a serine caseinase (Gudmundsdóttir and Gudmundsdóttir
1997 ; Schwenteit et al. 2015 ), phospholipase, haemolysins and a leucocidin (Munro
et al. 1980 ; Sheeran and Smith 1981 ; Shieh and MacLean 1975 ; Titball and Munn
1981 ; Cipriano et al. 1981 ; Fuller et al. 1977 ; Rockey et al. 1988 ; Huntly et al. 1992 ;
Lygren et al. 1998 ), as well as LPS. Work with monoclonal antibodies has shown
heterogeneity in the LPS (Rockey et al. 1991 ). Ellis et al. ( 1981 ) reported that ECP
of the pathogen, prepared by a cellophane overlay method, reproduced the lesions
normally associated with the chronic form of furunculosis, e.g. muscle necrosis and
Aeromonas salmonicida