469
Cultures were examined by 16S rRNA sequencing for which the nearest match
was Francisella philomiragia (99.3 % identity) and several apparent Francisella
from tilapia in Taiwan and three-lined grunt in Japan (Olsen et al. 2006 ). It was
considered that the isolate from Atlantic cod was more fastidious that Francisella
philomiragia (Olssen et al. 2006 ). Organisms were equated with two new species,
i.e. Fr. asiatica (= Fr. noatunensis subsp. orientalis) and Fr. noatunensis (Ottem
et al. 2009 ; Mikalsen and Colquhoun 2010 ). Fr. piscicida has a 99.8 % 16S rRNA
sequence homology with Fr. noatunensis, and was regarded as a heterotypic synonym of Fr. noatunensis (Mikalsen and Colquhoun 2010 ).
Separately, intracellular bacteria were found in the kidney and spleen of threeline grunt from which DNA was extracted and small subunit rRNA amplifi ed by
PCR, and sequenced. The outcome was 97.3–98.5 % homology to Francisella, with
Francisella philomiragia as the closest neighbour (Kamaishi et al. 2005 ). Originally,
Francisella philomiragia was classifi ed in Yersinia as Y. philomiragia, which comprised bacteria fi rst recovered from dying muskrat in Utah, USA (Jensen et al.
1969 ). The link to Yersinia resulted from the micro-morphology of the cells and
supposed DNA relatedness to Y. pestis (Ritter and Gerloff 1966 ). However, subsequent evaluation led to a transfer to Francisella (Hollis et al. 1989 ).
Diagnosis
Molecular Methods A specifi c quantitative real-time PCR has been developed for
the recognition of Fr. noatunensis subsp. orientalis, with a stated detection limit of
50 fg of DNA/reaction (= ~25 genome equivalents) (Soto et al. 2010a ).
Epizootiology
Experimental data suggested that Fr. noatunensis could pass through the digestive
tract of blue mussels ( Mytilus edulis ), and cells in the resulting faeces caused disease upon intraperitoneal injection of cod (Wangen et al. 2012 ). However, there was
not evidence that the pathogen remained in or even colonized blue mussel tissues.
Moreover, cohabitation of Atlantic cod with artifi cially infected blue mussels did
not lead to disease (Wangen et al. 2012 ).
Pathogenicity
Experimentally infected Atlantic cod did not develop any overt signs of disease and
only comparatively low numbers of fi sh challenged intraperitoneally succumbed
and died (Mikalsen et al. 2009 ). The organism replicated in adherent cells from
head kidney, and inhibited respiratory burst activity (this is probably important to
intracellular survival) in cod but not salmon leucocytes (Vestvik et al. 2013 ).
Francisella noatunensis
Cultures were examined by 16S rRNA sequencing for which the nearest match
was Francisella philomiragia (99.3 % identity) and several apparent Francisella
from tilapia in Taiwan and three-lined grunt in Japan (Olsen et al. 2006 ). It was
considered that the isolate from Atlantic cod was more fastidious that Francisella
philomiragia (Olssen et al. 2006 ). Organisms were equated with two new species,
i.e. Fr. asiatica (= Fr. noatunensis subsp. orientalis) and Fr. noatunensis (Ottem
et al. 2009 ; Mikalsen and Colquhoun 2010 ). Fr. piscicida has a 99.8 % 16S rRNA
sequence homology with Fr. noatunensis, and was regarded as a heterotypic synonym of Fr. noatunensis (Mikalsen and Colquhoun 2010 ).
Separately, intracellular bacteria were found in the kidney and spleen of threeline grunt from which DNA was extracted and small subunit rRNA amplifi ed by
PCR, and sequenced. The outcome was 97.3–98.5 % homology to Francisella, with
Francisella philomiragia as the closest neighbour (Kamaishi et al. 2005 ). Originally,
Francisella philomiragia was classifi ed in Yersinia as Y. philomiragia, which comprised bacteria fi rst recovered from dying muskrat in Utah, USA (Jensen et al.
1969 ). The link to Yersinia resulted from the micro-morphology of the cells and
supposed DNA relatedness to Y. pestis (Ritter and Gerloff 1966 ). However, subsequent evaluation led to a transfer to Francisella (Hollis et al. 1989 ).
Diagnosis
Molecular Methods A specifi c quantitative real-time PCR has been developed for
the recognition of Fr. noatunensis subsp. orientalis, with a stated detection limit of
50 fg of DNA/reaction (= ~25 genome equivalents) (Soto et al. 2010a ).
Epizootiology
Experimental data suggested that Fr. noatunensis could pass through the digestive
tract of blue mussels ( Mytilus edulis ), and cells in the resulting faeces caused disease upon intraperitoneal injection of cod (Wangen et al. 2012 ). However, there was
not evidence that the pathogen remained in or even colonized blue mussel tissues.
Moreover, cohabitation of Atlantic cod with artifi cially infected blue mussels did
not lead to disease (Wangen et al. 2012 ).
Pathogenicity
Experimentally infected Atlantic cod did not develop any overt signs of disease and
only comparatively low numbers of fi sh challenged intraperitoneally succumbed
and died (Mikalsen et al. 2009 ). The organism replicated in adherent cells from
head kidney, and inhibited respiratory burst activity (this is probably important to
intracellular survival) in cod but not salmon leucocytes (Vestvik et al. 2013 ).
Francisella noatunensis