537
1984 ; Kanemori et al. 1987 ). In particular, a zinc metalloprotease has been associated with invasion processes (Norquist et al. 1990 ). Crude ECP has led to the development of an infl ammatory response, including leucopenia, in rainbow trout (Lamas
et al. 1994a , b ). No doubt the debate will continue unabated for some considerable
period, but the ultimate result should be a better understanding of the pathogenicity
mechanisms. Basically at present, the scenario involves uptake and penetration of
the host tissues, scavenging for iron as a result of a plasmid/chromosomal mediated
trait, and damage to the fi sh by means of haemolysins and proteases. It is relevant to
note that an empA zinc metalloprotease, which is secreted as a ~46 kDa proenzyme
followed by extracellular activation involving removal of ~10 kDa peptide (Varina
et al. 2008 ), was detected during the stationary phase in strains which had been
incubated in Atlantic salmon gastro intestinal mucus (Denkin and Nelson 2004 ;
Staroscik et al. 2005 ). Is there a role for quorum sensing in controlling the expression of virulence genes? Homologs of four quorum sensing genes, coined VanT (this
was expressed at low cell density) , VanMN, VanPQ and VanOU, have been identifi ed
in V. anguillarum, and infl uence expression of the empA metalloprotease (Croxatto
et al. 2004 ). A conclusion is that V. anguillarum involves quorum sensing to regulate
stress responses necessary for survival, particularly in aquatic habitats (Weber et al.
2011 ).
Suppression subtractive hybridization (SSH) led to the recognition of a virulencerelated gene fragment, which was sequenced, and determined to encode a 547
amino acid putative membrane-bound lytic murein transglycosylase D (MltD) with
34 % homology to an equivalent in Esch. coli. A mltD mutant with reduced protease
and not haemolytic activity was constructed, which demonstrated enhanced virulence over the wild type strain following i.p. injection in a zebra fi sh model with the
resulting LD 50 dose of 1.01 × 10
2 CFU/fi sh and 3.92 × 10
3 CFU/fi sh, respectively.
mltD was cloned, and the recombinant MltD protein possessed diastrase, gelatinase,
haemolytic and phospholipase activities (Xu et al. 2011 ).
In a rather elegant set of experiments, Harbell et al. ( 1979 ) catalogued the precise
changes in the blood following infection with the pathogen. As anaemia is one of
the signs of vibriosis, it seems hardly surprising that the haemoglobin level decreases
concomitant with an increase in the erythrocyte osmotic fragility, and a decline in
the number of leucocytes. Reductions were also recorded in osmolarity, and in the
amounts of plasma protein, albumin, chloride, sodium and alkaline phosphate. In
contrast, levels of plasma glucose, lactate dehydrogenase, and glutamic oxaloacetic
transaminase increased.
Disease Control
Management Techniques Kocylowski ( 1963 ) recommended transfer of eels to
cold, well-aerated water to alleviate problems with vibriosis.
Vibrio anguillarum
1984 ; Kanemori et al. 1987 ). In particular, a zinc metalloprotease has been associated with invasion processes (Norquist et al. 1990 ). Crude ECP has led to the development of an infl ammatory response, including leucopenia, in rainbow trout (Lamas
et al. 1994a , b ). No doubt the debate will continue unabated for some considerable
period, but the ultimate result should be a better understanding of the pathogenicity
mechanisms. Basically at present, the scenario involves uptake and penetration of
the host tissues, scavenging for iron as a result of a plasmid/chromosomal mediated
trait, and damage to the fi sh by means of haemolysins and proteases. It is relevant to
note that an empA zinc metalloprotease, which is secreted as a ~46 kDa proenzyme
followed by extracellular activation involving removal of ~10 kDa peptide (Varina
et al. 2008 ), was detected during the stationary phase in strains which had been
incubated in Atlantic salmon gastro intestinal mucus (Denkin and Nelson 2004 ;
Staroscik et al. 2005 ). Is there a role for quorum sensing in controlling the expression of virulence genes? Homologs of four quorum sensing genes, coined VanT (this
was expressed at low cell density) , VanMN, VanPQ and VanOU, have been identifi ed
in V. anguillarum, and infl uence expression of the empA metalloprotease (Croxatto
et al. 2004 ). A conclusion is that V. anguillarum involves quorum sensing to regulate
stress responses necessary for survival, particularly in aquatic habitats (Weber et al.
2011 ).
Suppression subtractive hybridization (SSH) led to the recognition of a virulencerelated gene fragment, which was sequenced, and determined to encode a 547
amino acid putative membrane-bound lytic murein transglycosylase D (MltD) with
34 % homology to an equivalent in Esch. coli. A mltD mutant with reduced protease
and not haemolytic activity was constructed, which demonstrated enhanced virulence over the wild type strain following i.p. injection in a zebra fi sh model with the
resulting LD 50 dose of 1.01 × 10
2 CFU/fi sh and 3.92 × 10
3 CFU/fi sh, respectively.
mltD was cloned, and the recombinant MltD protein possessed diastrase, gelatinase,
haemolytic and phospholipase activities (Xu et al. 2011 ).
In a rather elegant set of experiments, Harbell et al. ( 1979 ) catalogued the precise
changes in the blood following infection with the pathogen. As anaemia is one of
the signs of vibriosis, it seems hardly surprising that the haemoglobin level decreases
concomitant with an increase in the erythrocyte osmotic fragility, and a decline in
the number of leucocytes. Reductions were also recorded in osmolarity, and in the
amounts of plasma protein, albumin, chloride, sodium and alkaline phosphate. In
contrast, levels of plasma glucose, lactate dehydrogenase, and glutamic oxaloacetic
transaminase increased.
Disease Control
Management Techniques Kocylowski ( 1963 ) recommended transfer of eels to
cold, well-aerated water to alleviate problems with vibriosis.
Vibrio anguillarum