631
characterized by the huge populations of segmented, fi lamentous bacteria in the
digestive tract, and daily losses of 0.5–1 % (Michel et al. 2002 ). Affected fi sh are
lethargic and inappetant, and yellow, mucoid faeces may extend from the vent. The
digestive tract is haemorrhagic and odematous, and fi lled with mucoid material
(Michel et al. 2002 ). Isolation of bacteria with the morphological characteristics of
‘ Candidatus Arthromitus’ was not achieved (Michel et al. 2002 ). However, the
pathogen could be detected using a nested PCR, bot blotting and Southern blotting
material from the digestive tract of rainbow trout (Del-Pozo et al. 2010 ; Cecchini
et al. 2012 ). By the nested PCR, positivity was recorded in the distal intestine and
pyloric caeca of rainbow trout displaying signs of gastro-enteritis (Del-Pozo et al.
2010 ). Possibly, the organism comprises part of the normal microfl ora of the digestive tract (Michel et al. 2002a ). Alternatively, it is feasible that the organism could
be introduced via feed. Pathogenicity may involve an unspecifi ed toxin (Michel
et al. 2002 ).
‘ Candidatus Branchiomonas cysticola’
Atlantic salmon, which were farmed in Norway, displayed gill epitheliocystis, from
which ‘ Candidatus Piscichlamydia salmonis’ was recognized by PCR together with
another organism (Toenshoff et al. 2012 ). The new bacterium, which was regarded
as responsible for the formation of the cysts, was recognized by 16S rRNA methods
as a new ß-proteobacterial representative, and, coined ‘ Candidatus Branchiomonas
cysticola’. Reticulate and intermediate bodies but not the elementary bodies typical
of chlamydia were observed in the cysts as described previously from salmon
(Toenshoff et al. 2012 ). Thus, the authors regarded that this form of epitheliocystis
was caused by a novel agent phylogenetically distinct from the Chlamydiae.
Since its original description, the pathogen has been recognized in farmed Atlantic
salmon in Ireland (Mitchell et al. 2013 ). To aid diagnosis, a highly sensitive and specifi c RT-PCR was developed, and as a result of its use, the dominance of the organism
in epitheliocystis in Ireland and Norway was recognized (Mitchell et al. 2013 ).
‘ Candidatus Clavochlamydia salmonicola’
Chlamydia are obligate intracellular parasites, and one group in particular has been
linked to a disease of Norwegian salmonids from freshwater involving the formation of unicellular cysts in epithelial tissues, i.e. epitheliocystis. Cells have been
observed, and described as are pleomorphic of up to 2 μm in length, and have a
developmental cycle similar to that of the Chlamydia (Karlsen et al. 2008 ). Based
on sequencing of the partial 16S rRNA gene, the causal agent has been linked the
Chlamydiaceae, and the name ‘ Candidatus Clavochlamydia salmonicola’ proposed
(Karlsen et al. 2008 ).
‘Candidatus’
characterized by the huge populations of segmented, fi lamentous bacteria in the
digestive tract, and daily losses of 0.5–1 % (Michel et al. 2002 ). Affected fi sh are
lethargic and inappetant, and yellow, mucoid faeces may extend from the vent. The
digestive tract is haemorrhagic and odematous, and fi lled with mucoid material
(Michel et al. 2002 ). Isolation of bacteria with the morphological characteristics of
‘ Candidatus Arthromitus’ was not achieved (Michel et al. 2002 ). However, the
pathogen could be detected using a nested PCR, bot blotting and Southern blotting
material from the digestive tract of rainbow trout (Del-Pozo et al. 2010 ; Cecchini
et al. 2012 ). By the nested PCR, positivity was recorded in the distal intestine and
pyloric caeca of rainbow trout displaying signs of gastro-enteritis (Del-Pozo et al.
2010 ). Possibly, the organism comprises part of the normal microfl ora of the digestive tract (Michel et al. 2002a ). Alternatively, it is feasible that the organism could
be introduced via feed. Pathogenicity may involve an unspecifi ed toxin (Michel
et al. 2002 ).
‘ Candidatus Branchiomonas cysticola’
Atlantic salmon, which were farmed in Norway, displayed gill epitheliocystis, from
which ‘ Candidatus Piscichlamydia salmonis’ was recognized by PCR together with
another organism (Toenshoff et al. 2012 ). The new bacterium, which was regarded
as responsible for the formation of the cysts, was recognized by 16S rRNA methods
as a new ß-proteobacterial representative, and, coined ‘ Candidatus Branchiomonas
cysticola’. Reticulate and intermediate bodies but not the elementary bodies typical
of chlamydia were observed in the cysts as described previously from salmon
(Toenshoff et al. 2012 ). Thus, the authors regarded that this form of epitheliocystis
was caused by a novel agent phylogenetically distinct from the Chlamydiae.
Since its original description, the pathogen has been recognized in farmed Atlantic
salmon in Ireland (Mitchell et al. 2013 ). To aid diagnosis, a highly sensitive and specifi c RT-PCR was developed, and as a result of its use, the dominance of the organism
in epitheliocystis in Ireland and Norway was recognized (Mitchell et al. 2013 ).
‘ Candidatus Clavochlamydia salmonicola’
Chlamydia are obligate intracellular parasites, and one group in particular has been
linked to a disease of Norwegian salmonids from freshwater involving the formation of unicellular cysts in epithelial tissues, i.e. epitheliocystis. Cells have been
observed, and described as are pleomorphic of up to 2 μm in length, and have a
developmental cycle similar to that of the Chlamydia (Karlsen et al. 2008 ). Based
on sequencing of the partial 16S rRNA gene, the causal agent has been linked the
Chlamydiaceae, and the name ‘ Candidatus Clavochlamydia salmonicola’ proposed
(Karlsen et al. 2008 ).
‘Candidatus’