6.7
Pseudomonas fluorescens
The ubiquitous bacterium Pseudomonas fluorescens is generally considered as a non-pathogenic saprophyte, however,
it can become an opportunistic pathogen causing disease in
wild and farmed salmonids, particularly following stress and
periods of poor water quality. Under farming conditions
outbreaks can occur after vaccination or concurrent to
other disease (e.g. infectious pancreatic necrosis). Smolts
suffering from subclinical disease during smoltification and
sea-water transfer may show clinical disease during the sea
water phase. Affected fish may display many different
manifestations of disease, from chronic, non-symptomatic,
to acute haemorrhagic septicaemia, with high mortality
(>15 %). External signs may include exophthalmia, frayed
fins or fin rot, skin ulcerations with haemorrhagic edges,
ventral petechiae and dark colouration (Fig. 6.20). At
necropsy, changes are similar to other bacterial conditions,
including ascites, petechiae on internal organs and pale liver,
but a purulent epicarditis can also be observed (Fig. 6.21).
Histopathological lesions include septic thrombi with
bacterial colonies in the gill lamellae, bacteria in spleen,
kidney and heart plus epicarditis. Other Pseudomonas spp.,
including P. anguilliseptica can also cause disease in both
wild and farmed salmonids with similar clinical and pathological manifestations.
Pseudomonas fluorescens is motile Gram negative rodshaped bacterium found in soil, freshwater and on plant
surfaces. It produces a water-soluble yellow-green pigment
which fluoresces under UV-light. Diagnosis is based upon
isolation and characterization of the causative bacterium on
enrichment medium and immunohistochemistry.
Fig. 6.17 Enteric redmouth in farmed rainbow trout; petecchia in peripancreatic tissues
Fig. 6.18 Bacteria in glomerular vessels and thickened basal membrane in rainbow trout infected with Yersinia ruckeri. Bar ¼ 50 μm
Fig. 6.19 Meningitis in farmed rainbow trout with enteric redmouth.
Immunohistochemical stain
6.7 Pseudomonas fluorescens
81
Pseudomonas fluorescens
The ubiquitous bacterium Pseudomonas fluorescens is generally considered as a non-pathogenic saprophyte, however,
it can become an opportunistic pathogen causing disease in
wild and farmed salmonids, particularly following stress and
periods of poor water quality. Under farming conditions
outbreaks can occur after vaccination or concurrent to
other disease (e.g. infectious pancreatic necrosis). Smolts
suffering from subclinical disease during smoltification and
sea-water transfer may show clinical disease during the sea
water phase. Affected fish may display many different
manifestations of disease, from chronic, non-symptomatic,
to acute haemorrhagic septicaemia, with high mortality
(>15 %). External signs may include exophthalmia, frayed
fins or fin rot, skin ulcerations with haemorrhagic edges,
ventral petechiae and dark colouration (Fig. 6.20). At
necropsy, changes are similar to other bacterial conditions,
including ascites, petechiae on internal organs and pale liver,
but a purulent epicarditis can also be observed (Fig. 6.21).
Histopathological lesions include septic thrombi with
bacterial colonies in the gill lamellae, bacteria in spleen,
kidney and heart plus epicarditis. Other Pseudomonas spp.,
including P. anguilliseptica can also cause disease in both
wild and farmed salmonids with similar clinical and pathological manifestations.
Pseudomonas fluorescens is motile Gram negative rodshaped bacterium found in soil, freshwater and on plant
surfaces. It produces a water-soluble yellow-green pigment
which fluoresces under UV-light. Diagnosis is based upon
isolation and characterization of the causative bacterium on
enrichment medium and immunohistochemistry.
Fig. 6.17 Enteric redmouth in farmed rainbow trout; petecchia in peripancreatic tissues
Fig. 6.18 Bacteria in glomerular vessels and thickened basal membrane in rainbow trout infected with Yersinia ruckeri. Bar ¼ 50 μm
Fig. 6.19 Meningitis in farmed rainbow trout with enteric redmouth.
Immunohistochemical stain
6.7 Pseudomonas fluorescens
81