133
Characteristics of the Pathogen
Organisms were cultured from Chinook salmon (Backman et al. 1990 ) and Atlantic
salmon (Claveau 1991 ) and linked to Rhodococcus (Claveau 1991 ).
Epizootiology
It was considered that feeding with crude fi sh offal may have been the cause of
infection (Claveau 1991 ).
Pathogenicity
Intraperitoneal injection of Atlantic salmon smolts with a very high dose of 5 × 10
8
cells resulted in severe peritoneal granulomatous reactions, with a low accompanying mortality rate, within 21 days (Speare et al. 1995 ). Unlike the natural disease
where the most severe pathological changes occurred in the renal interstitium,
experimental challenge resulted in damage in the direct vicinity of the injection site.
Yet, the development of large bacterial colonies were common to both natural and
artifi cial infections.
Rhodococcus erythropolis
Characteristics of the Disease
Fresh-and seawater reared Atlantic salmon, which had been previously intraperitoneally injected with oil-adjuvanted vaccine of more than one manufacturer in
Norway (5 cases) and Scotland (2 cases), experienced losses of 1–35 %. The systemic infection centred on the peritoneal cavity, and moribund fi sh displayed scale
loss and occasionally cutaneous haemorrhages in the abdomen and at the base of the
fi ns. In addition, there was some evidence of abdominal distension. In Scotland,
Box 3.19: Rhodococcus sp.
Isolates comprise non-acid-fast facultatively anaerobic Gram-positive rods
(2–3 × 0.6 μm in size) [slightly club shaped], which grow aerobically at room
temperature (but not at 37 °C) on blood agar in 3–4 days. The cell wall components include meso -diaminopimelic acid, arabinose and galactose, which
equates with chemotype IVA, N-glycolated muramic acid, mycolic acids, and
MK-8 as the predominant isoprenoid menaquinone. Neither catalase nor oxidase is produced. Urea is degraded. Xylose is fermented, but not so glucose,
lactose, maltose or sucrose. Acid is produced from meso -inositol but not from
dulcitol, mannitol or sorbitol. Growth occurs in 5 % (w/v) sodium chloride.
Nocardiaceae Representatives
Characteristics of the Pathogen
Organisms were cultured from Chinook salmon (Backman et al. 1990 ) and Atlantic
salmon (Claveau 1991 ) and linked to Rhodococcus (Claveau 1991 ).
Epizootiology
It was considered that feeding with crude fi sh offal may have been the cause of
infection (Claveau 1991 ).
Pathogenicity
Intraperitoneal injection of Atlantic salmon smolts with a very high dose of 5 × 10
8
cells resulted in severe peritoneal granulomatous reactions, with a low accompanying mortality rate, within 21 days (Speare et al. 1995 ). Unlike the natural disease
where the most severe pathological changes occurred in the renal interstitium,
experimental challenge resulted in damage in the direct vicinity of the injection site.
Yet, the development of large bacterial colonies were common to both natural and
artifi cial infections.
Rhodococcus erythropolis
Characteristics of the Disease
Fresh-and seawater reared Atlantic salmon, which had been previously intraperitoneally injected with oil-adjuvanted vaccine of more than one manufacturer in
Norway (5 cases) and Scotland (2 cases), experienced losses of 1–35 %. The systemic infection centred on the peritoneal cavity, and moribund fi sh displayed scale
loss and occasionally cutaneous haemorrhages in the abdomen and at the base of the
fi ns. In addition, there was some evidence of abdominal distension. In Scotland,
Box 3.19: Rhodococcus sp.
Isolates comprise non-acid-fast facultatively anaerobic Gram-positive rods
(2–3 × 0.6 μm in size) [slightly club shaped], which grow aerobically at room
temperature (but not at 37 °C) on blood agar in 3–4 days. The cell wall components include meso -diaminopimelic acid, arabinose and galactose, which
equates with chemotype IVA, N-glycolated muramic acid, mycolic acids, and
MK-8 as the predominant isoprenoid menaquinone. Neither catalase nor oxidase is produced. Urea is degraded. Xylose is fermented, but not so glucose,
lactose, maltose or sucrose. Acid is produced from meso -inositol but not from
dulcitol, mannitol or sorbitol. Growth occurs in 5 % (w/v) sodium chloride.
Nocardiaceae Representatives