374
1983 ). The LD 50 dose has been established to be 3.0 × 10
5 cells/ml for Type 1,
1.0 × 10
7 cells/ml for Type 2 and an as yet undetermined dose for Type 3. The degree
of pathogenicity of serovars IV and V needs clarifi cation. The new biogroup, biotype 2, described by Austin et al. ( 2005 ) killed rainbow trout within 4-days at a dose
of 10
5 cells/fi sh. It is possible that the BarA-UvrY two component system contributes to pathogenesis by regulating invasion of epithelial cells and sensitivity to oxidative stress induced by immune cells (Dahiya and Stevenson 2010a ). Also, the
ZnuABC high affi nity zinc transporter has a role in the infection cycle (Dahiya and
Stevenson 2010b ). It should be emphasised that exposure to sublethal concentrations of copper, i.e. 7 μg/l for 96 h, rendered the fi sh more susceptible to infection
by Y. ruckeri (Knittel 1981 ). Moreover, the nature of the virulence factors is incompletely understood. The role of plasmids in virulence has been indicated insofar as
the more pathogenic Type 1 isolates possess a large 40–50 mDa plasmid, and some
contain a smaller 20–30 mDa plasmid. The larger plasmid is absent from Type 2
cultures (Cook and Gemski 1982 ; De Grandis and Stevenson 1985 ). Further work
is necessary, however, to resolve the precise role of this large plasmid in pathogenicity, especially as it is not thought to carry virulence factors (Guilvout et al. 1988 ).
The O antigen, from the LPS of serogroup O1, has been determined to comprise
a branched tetrasaccharide, with repeating units containing 2-acetamidino-2,6dideoxy- L-galactose, 2-acetamido-2-deoxy-D-glucose and 7-acetamido-3,5,7,9tetradeoxy- 5-(4-hydroxybutyramido)-D-glycero-L-galacto-nonulosonic
acid
(Beynon et al. 1994 ), and is regarded as the dominant immunogenic molecule
(Costa et al. 2011 ).
ECP have been recovered, and demonstrated to have an LD 50 of 2–9.12 μg of
protein/g of fi sh. The ECP has been found to contain amylase, caseinase, gelatinase,
haemolytic (salmon, sheep and trout erythrocytes) lipase and phospholipase activity. Haemolysin Yh1A is expressed more so at 18 °C [the temperature of many disease outbreaks] than 28 °C, and is further increased in iron-depleted conditions
(Fernández et al. 2007 ). A novel 47 kDa azocasein hydrolyzing protease, which was
produced during the end of the exponential growth phase, was recovered from culture supernatants (Secades and Guijarro 1999 ). Later, a serralysin metalloprotease
(= metalloendopeptidase), termed Yrp1, that hydrolyses actin, fi brinogen, gelatin,
laminin and myson (but not type II and type IV collagen) has been linked to pathogenicity (Fernández et al. 2002 , 2003 ). Also, aesculin has been attacked (Romalde
and Toranzo 1993 ). Adhesin activity, at least to the CHSE-214 cell culture, has been
recorded (Romalde and Toranzo 1993 ).
Evidence has been presented that Y. ruckeri may have a siderophore mediated
iron uptake system (Romalde et al. 1991 ; Fernández et al. 2004 ), in parallel to Aer.
salmonicida and V. anguillarum. Romalde and colleagues revealed that >3 OMP
were induced in iron limiting conditions. Ruckerbactin, a catecholate siderophore
iron acquisition system, has been described (Fernández et al. 2004 ). As a result of a
commendable study, Davies ( 1991 ) reported on the OMP of 135 Y. ruckeri isolates.
Several 36.5–40.5 kDa peptidoglycan associated proteins and a 36.5 or 38 kDa
heat- modifi able protein were characterised. This 39.5 kDa peptidoglycan-associ6 Enterobacteriaceae Representatives
1983 ). The LD 50 dose has been established to be 3.0 × 10
5 cells/ml for Type 1,
1.0 × 10
7 cells/ml for Type 2 and an as yet undetermined dose for Type 3. The degree
of pathogenicity of serovars IV and V needs clarifi cation. The new biogroup, biotype 2, described by Austin et al. ( 2005 ) killed rainbow trout within 4-days at a dose
of 10
5 cells/fi sh. It is possible that the BarA-UvrY two component system contributes to pathogenesis by regulating invasion of epithelial cells and sensitivity to oxidative stress induced by immune cells (Dahiya and Stevenson 2010a ). Also, the
ZnuABC high affi nity zinc transporter has a role in the infection cycle (Dahiya and
Stevenson 2010b ). It should be emphasised that exposure to sublethal concentrations of copper, i.e. 7 μg/l for 96 h, rendered the fi sh more susceptible to infection
by Y. ruckeri (Knittel 1981 ). Moreover, the nature of the virulence factors is incompletely understood. The role of plasmids in virulence has been indicated insofar as
the more pathogenic Type 1 isolates possess a large 40–50 mDa plasmid, and some
contain a smaller 20–30 mDa plasmid. The larger plasmid is absent from Type 2
cultures (Cook and Gemski 1982 ; De Grandis and Stevenson 1985 ). Further work
is necessary, however, to resolve the precise role of this large plasmid in pathogenicity, especially as it is not thought to carry virulence factors (Guilvout et al. 1988 ).
The O antigen, from the LPS of serogroup O1, has been determined to comprise
a branched tetrasaccharide, with repeating units containing 2-acetamidino-2,6dideoxy- L-galactose, 2-acetamido-2-deoxy-D-glucose and 7-acetamido-3,5,7,9tetradeoxy- 5-(4-hydroxybutyramido)-D-glycero-L-galacto-nonulosonic
acid
(Beynon et al. 1994 ), and is regarded as the dominant immunogenic molecule
(Costa et al. 2011 ).
ECP have been recovered, and demonstrated to have an LD 50 of 2–9.12 μg of
protein/g of fi sh. The ECP has been found to contain amylase, caseinase, gelatinase,
haemolytic (salmon, sheep and trout erythrocytes) lipase and phospholipase activity. Haemolysin Yh1A is expressed more so at 18 °C [the temperature of many disease outbreaks] than 28 °C, and is further increased in iron-depleted conditions
(Fernández et al. 2007 ). A novel 47 kDa azocasein hydrolyzing protease, which was
produced during the end of the exponential growth phase, was recovered from culture supernatants (Secades and Guijarro 1999 ). Later, a serralysin metalloprotease
(= metalloendopeptidase), termed Yrp1, that hydrolyses actin, fi brinogen, gelatin,
laminin and myson (but not type II and type IV collagen) has been linked to pathogenicity (Fernández et al. 2002 , 2003 ). Also, aesculin has been attacked (Romalde
and Toranzo 1993 ). Adhesin activity, at least to the CHSE-214 cell culture, has been
recorded (Romalde and Toranzo 1993 ).
Evidence has been presented that Y. ruckeri may have a siderophore mediated
iron uptake system (Romalde et al. 1991 ; Fernández et al. 2004 ), in parallel to Aer.
salmonicida and V. anguillarum. Romalde and colleagues revealed that >3 OMP
were induced in iron limiting conditions. Ruckerbactin, a catecholate siderophore
iron acquisition system, has been described (Fernández et al. 2004 ). As a result of a
commendable study, Davies ( 1991 ) reported on the OMP of 135 Y. ruckeri isolates.
Several 36.5–40.5 kDa peptidoglycan associated proteins and a 36.5 or 38 kDa
heat- modifi able protein were characterised. This 39.5 kDa peptidoglycan-associ6 Enterobacteriaceae Representatives