510
Vale et al. 2002 ). The surface-located 22–38 kDa sialic acid, which may inhibit the
complement cascade and thus protect the pathogen from the host’s antibodies, has a
possible role in cell adhesion and survival in the host (Jung et al. 2000 ). Another
study reported that cells of the pathogen were killed by macrophages in vitro in
3–5 h (Skarmeta et al. 1995 ). Yet, the ability to induce apoptosis and thence lysis of
sea bass macrophages and neutrophils has been linked to a plasmid-encoded 56 kDa
protein, coined AIP56, which was secreted by virulent but not avirulent cultures (do
Vale et al. 2002 , 2005 ). Interestingly, passive immunisation with rabbit antiserum
against this protein led to protection (do Vale et al. 2005 ). Using the EPC cell line,
bacterial cells were seen to adhere to and become internalized by the cells within
vacuoles possibly by endocytosis, remaining intracellular for 6–9 h. Intracellular
multiplication was not recorded (López-Dóriga et al. 2000 ). Increased catalase
activity, which is inversely related to the quantity of iron, has been detected in virulent compared to non-virulent cultures leading to the thought that this enzyme may
well be involved in survival within the host (Díaz-Rosales et al. 2006 ).
Resistance to the pathogen may well refl ect the size of the fi sh and the effi ciency
of the phagocytes (Noya et al. 1995 ). There is a distinct role for the capsule to protect against phagocytosis (Arijo et al. 1998 ) and, in immunised fi sh, protection
against complement-mediated killing (Acosta et al. 2006 ). Comparing fi ve capsulated, virulent and 1 non-capsulated, avirulent culture, Arijo et al. ( 1998 ) recorded
signifi cant differences in phagocytosis with the former resisting being engulfed and
killed by the macrophages. In a separate development, it was considered that mucus
from turbot – thought to contain a glycoprotein – inhibited Ph. damselae subsp .
piscicida, but less so mucus from sea bass and sea bream (Magariños et al. 1995 ).
Perhaps, such observations explain the comparative sensitivity of some fi sh species,
e.g. sea bass and sea bream, to the pathogen.
A siderophore-mediated iron sequestering mechanism has been found in Ph.
damselae subsp. piscicida , with IROMPs of 105, 118 and 145 kDa in size (Magariños
et al. 1994b ). Some variability has been detected insofar as isolates expressed a
75 kDa IROMP. Also, others have reported different sizes for the novel proteins
associated with iron limitation. Thus, European isolates were considered to express
four novel proteins of 63 kDa and three at ≥200 kDa, whereas Japanese isolates did
not form any different proteins (Bakopoulos et al. 1997b ). Bakopoulos et al. ( 2004 )
reported a novel >206 kDa protein associated with iron sequestration. Indeed, high
levels of iron, i.e. 200 mg of iron/kg of feed and 2.5 % carbonyl iron to separate
groups, in the diet were found to adversely infl uence the pathogenicity of Ph. damselae subsp. piscicida in sea bass (Rodrigues and Pereira 2004 ). In the carbonyl iron
treated group, 64 % of the fi sh died after challenge compared to only 9 % of the
controls.
The pathogen utilizes haem compounds as the sole source of iron. Work has
determined the presence of a gene cluster with 10 haem uptake and utilization
genes, of which hutC and hutD are iron-regulated, and are expressed during infection (Osorio et al. 2010 ).
10 Vibrios
Vale et al. 2002 ). The surface-located 22–38 kDa sialic acid, which may inhibit the
complement cascade and thus protect the pathogen from the host’s antibodies, has a
possible role in cell adhesion and survival in the host (Jung et al. 2000 ). Another
study reported that cells of the pathogen were killed by macrophages in vitro in
3–5 h (Skarmeta et al. 1995 ). Yet, the ability to induce apoptosis and thence lysis of
sea bass macrophages and neutrophils has been linked to a plasmid-encoded 56 kDa
protein, coined AIP56, which was secreted by virulent but not avirulent cultures (do
Vale et al. 2002 , 2005 ). Interestingly, passive immunisation with rabbit antiserum
against this protein led to protection (do Vale et al. 2005 ). Using the EPC cell line,
bacterial cells were seen to adhere to and become internalized by the cells within
vacuoles possibly by endocytosis, remaining intracellular for 6–9 h. Intracellular
multiplication was not recorded (López-Dóriga et al. 2000 ). Increased catalase
activity, which is inversely related to the quantity of iron, has been detected in virulent compared to non-virulent cultures leading to the thought that this enzyme may
well be involved in survival within the host (Díaz-Rosales et al. 2006 ).
Resistance to the pathogen may well refl ect the size of the fi sh and the effi ciency
of the phagocytes (Noya et al. 1995 ). There is a distinct role for the capsule to protect against phagocytosis (Arijo et al. 1998 ) and, in immunised fi sh, protection
against complement-mediated killing (Acosta et al. 2006 ). Comparing fi ve capsulated, virulent and 1 non-capsulated, avirulent culture, Arijo et al. ( 1998 ) recorded
signifi cant differences in phagocytosis with the former resisting being engulfed and
killed by the macrophages. In a separate development, it was considered that mucus
from turbot – thought to contain a glycoprotein – inhibited Ph. damselae subsp .
piscicida, but less so mucus from sea bass and sea bream (Magariños et al. 1995 ).
Perhaps, such observations explain the comparative sensitivity of some fi sh species,
e.g. sea bass and sea bream, to the pathogen.
A siderophore-mediated iron sequestering mechanism has been found in Ph.
damselae subsp. piscicida , with IROMPs of 105, 118 and 145 kDa in size (Magariños
et al. 1994b ). Some variability has been detected insofar as isolates expressed a
75 kDa IROMP. Also, others have reported different sizes for the novel proteins
associated with iron limitation. Thus, European isolates were considered to express
four novel proteins of 63 kDa and three at ≥200 kDa, whereas Japanese isolates did
not form any different proteins (Bakopoulos et al. 1997b ). Bakopoulos et al. ( 2004 )
reported a novel >206 kDa protein associated with iron sequestration. Indeed, high
levels of iron, i.e. 200 mg of iron/kg of feed and 2.5 % carbonyl iron to separate
groups, in the diet were found to adversely infl uence the pathogenicity of Ph. damselae subsp. piscicida in sea bass (Rodrigues and Pereira 2004 ). In the carbonyl iron
treated group, 64 % of the fi sh died after challenge compared to only 9 % of the
controls.
The pathogen utilizes haem compounds as the sole source of iron. Work has
determined the presence of a gene cluster with 10 haem uptake and utilization
genes, of which hutC and hutD are iron-regulated, and are expressed during infection (Osorio et al. 2010 ).
10 Vibrios