423
organism causes skin lesions, which are often described as saddle-like lesions, containing myriads of organisms, near the dorsal fi n. The fi sh may darken and, in
advanced cases, develop bacteraemia with the pathogen ramifying throughout the
animal (Wood and Yasutake 1956 ; Winton et al. 1983; Lehmann et al. 1991 ). A
systemic infection of rainbow trout has been described in Norway, the outcome of
which was mortalities of ~90 % (Nilsen et al. 2011a ). Here, the disease in fry was
characterized by anorexia, distended abdomen, and darkened pigmentation in the
region of the caudal peduncle. Larger fi sh were lethargic, and often displayed skin
ulceration (Nilsen et al. 2011a ). The organism has also been linked with septicaemia
and necrotic myositis (accumulated loss of 7 %) in Atlantic salmon smolts of
60—100 g in size from a freshwater site in Norway during winter (water temperature = <5 °C) (Nilsen et al. 2011b ). The fi sh displayed swollen darkened spleen, pale
live, bloody ascites and haemorrhaging in the abdominal fat and muscle (Nilsen
et al. 2011b ).
Isolation
Specialised media have been devised, of which cytophaga agar (Appendix in
Chap. 12 ; after Anacker and Ordal 1959 ) has received greatest use for the recovery
of Fla. psychrophilum. An improved growth medium has been published with the
outcome that more rapid and luxuriant growth occurred; the recipe was based on
cytophaga agar/broth supplemented with galactose, glucose, rhamnose and skimmed
milk (Appendix in Chap. 12 ; Daskalov et al. 1999 ). Then, Cepeda et al. ( 2004 )
reported that a glucose, salt, tryptone and yeast extract based medium, coined FLP,
was superior for speed and abundance of growth of the pathogen (Appendix in
Chap. 12 ). Cytophaga agar supplemented with 0.2 % skimmed milk and 1 % horse
serum gave a slight improvement in growth (Oplinger and Wagner 2012 ). An alternative approach was to add 5 μg/l of the aminoglycoside antibiotic tobramycin,
which was stated to improve recovery of Fla. psychrophilum especially from the
external surfaces of carrier ayu (Kumagai et al. 2004a ). Caution has been suggested
over the source of ingredients used to make some media. For example, the importance of the brand of beef extract (the Difco product was reported as superior to
Gibco or Oxoid) for the growth of Fla. psychrophilum on cytophaga agar was highlighted by Lorenzen ( 1993 ). Improved recovery of viable cells of Fla. psychrophilum from dilute samples was achieved using nutrient agar supplemented with
activated charcoal (Appendix in Chap. 12 ; Álvarez and Guijarro 2007 ).
Characteristics of the Pathogen
The best of the descriptions of this organism stems from the work of Pacha ( 1968 ),
Bernardet and Kerouault ( 1989 ), Bernardet and Grimont ( 1989 b) and Schmidtke
and Carson ( 1995 ). Opinion is that this pathogen comprises a phenotypically
Flavobacterium psychrophilum
organism causes skin lesions, which are often described as saddle-like lesions, containing myriads of organisms, near the dorsal fi n. The fi sh may darken and, in
advanced cases, develop bacteraemia with the pathogen ramifying throughout the
animal (Wood and Yasutake 1956 ; Winton et al. 1983; Lehmann et al. 1991 ). A
systemic infection of rainbow trout has been described in Norway, the outcome of
which was mortalities of ~90 % (Nilsen et al. 2011a ). Here, the disease in fry was
characterized by anorexia, distended abdomen, and darkened pigmentation in the
region of the caudal peduncle. Larger fi sh were lethargic, and often displayed skin
ulceration (Nilsen et al. 2011a ). The organism has also been linked with septicaemia
and necrotic myositis (accumulated loss of 7 %) in Atlantic salmon smolts of
60—100 g in size from a freshwater site in Norway during winter (water temperature = <5 °C) (Nilsen et al. 2011b ). The fi sh displayed swollen darkened spleen, pale
live, bloody ascites and haemorrhaging in the abdominal fat and muscle (Nilsen
et al. 2011b ).
Isolation
Specialised media have been devised, of which cytophaga agar (Appendix in
Chap. 12 ; after Anacker and Ordal 1959 ) has received greatest use for the recovery
of Fla. psychrophilum. An improved growth medium has been published with the
outcome that more rapid and luxuriant growth occurred; the recipe was based on
cytophaga agar/broth supplemented with galactose, glucose, rhamnose and skimmed
milk (Appendix in Chap. 12 ; Daskalov et al. 1999 ). Then, Cepeda et al. ( 2004 )
reported that a glucose, salt, tryptone and yeast extract based medium, coined FLP,
was superior for speed and abundance of growth of the pathogen (Appendix in
Chap. 12 ). Cytophaga agar supplemented with 0.2 % skimmed milk and 1 % horse
serum gave a slight improvement in growth (Oplinger and Wagner 2012 ). An alternative approach was to add 5 μg/l of the aminoglycoside antibiotic tobramycin,
which was stated to improve recovery of Fla. psychrophilum especially from the
external surfaces of carrier ayu (Kumagai et al. 2004a ). Caution has been suggested
over the source of ingredients used to make some media. For example, the importance of the brand of beef extract (the Difco product was reported as superior to
Gibco or Oxoid) for the growth of Fla. psychrophilum on cytophaga agar was highlighted by Lorenzen ( 1993 ). Improved recovery of viable cells of Fla. psychrophilum from dilute samples was achieved using nutrient agar supplemented with
activated charcoal (Appendix in Chap. 12 ; Álvarez and Guijarro 2007 ).
Characteristics of the Pathogen
The best of the descriptions of this organism stems from the work of Pacha ( 1968 ),
Bernardet and Kerouault ( 1989 ), Bernardet and Grimont ( 1989 b) and Schmidtke
and Carson ( 1995 ). Opinion is that this pathogen comprises a phenotypically
Flavobacterium psychrophilum