633
Unidentifi ed Gram-Negative Bacteria
There is an increasing awareness of diseases caused by apparently unique bacteria.
For example, Sorimachi et al. ( 1993 ) and Iida and Sorimachi ( 1994 ) described jaundice in yellowtail, attributed to an unknown fi lamentous bacterium of 4–6 μm in
length, which grew only in L15 medium and Eagles MEM medium each supplemented with 10 % (v/v) foetal calf serum at 23–26 °C.
The human and animal pathology literature abounds with references to hard-toidentify or unidentifi ed pathogens. An example from fi sh pathology concerns a hitherto unknown intracellular bacterial pathogen of farmed Atlantic salmon in Ireland
(Palmer et al. 1994 ). During 1992–1993 when the water temperature was 8–9 and
15–16 °C, fi sh became lethargic, swam close to the water surface, and displayed
loss of balance. Apart from an infestation of salmon lice, the fi sh revealed the presence of petechia or haemorrhagic areas on the abdominal walls, petechia on the
pyloric caeca and swim bladder, congestion of the kidney and spleen, splenomegaly,
and kidney swelling. The fore and hind guts contained white mucus. Some fi sh had
pale friable livers, pale spleens, visceral adhesions, and false membranes in the
peritoneum (Palmer et al. 1994 ). The intracellular Gram-negative cocco-bacilli
required serum or blood for growth, which was accomplished on 7 % (v/v) horse
blood agar and 10 % (v/v) foetal calf serum medium after 4–14 days incubation at
15 or 22 °C (Palmer et al. 1994 ).
The organism was linked tenuously to the Neisseriaceae and Pasteurellaceae.,
although the rickettsias may be an appropriate home. According to Palmer et al .
( 1994 ) infectivity was achieved by injecting cells into Atlantic salmon, which
became moribund after 6–10 days, and died within 30 days. Moribund fi sh disBox 11.15: Unknown Gram-Negative Organism of Palmer et al . ( 1994 )
Cultures produce small colonies of 0.3 mm in diameter after incubation aerobically for 10–14 days. Anaerobic incubation results in larger colonies of
0.6 mm in diameter. Improved growth results by the addition of 0.5 mg of
L-cysteine hydrochloride/l. Colonies are off-white, convex and granular, and
contain non-motile, Gram-negative ß-haemolytic cocco-bacilli. Alkaline
phosphatase (weakly positive/variable), arginine dihydrolase, H 2 S (weakly
positive/variable), indole (weakly positive/variable) and lipases are produced,
but not α-glucosidase, N-acetyl glucosamine, catalase, ß-galactosidase,
ß-glucuronidase, lysine decarboxylase or oxidase. Nitrates are not reduced.
The Voges Proskauer reaction is negative. Neither aesculin, gelatin, Tween 80
nor urea is attacked. Citrate is not utilised. Fructose, glucose and maltose are
fermented, but not glycogen, lactose, mannitol, mannose, ribose, sucrose or
xylose. Growth occurs at 10 °C but not at 37 °C, and in 1–4 but not 5 % (w/v)
sodium chloride.
Unidentifi ed Gram-Negative Bacteria
Unidentifi ed Gram-Negative Bacteria
There is an increasing awareness of diseases caused by apparently unique bacteria.
For example, Sorimachi et al. ( 1993 ) and Iida and Sorimachi ( 1994 ) described jaundice in yellowtail, attributed to an unknown fi lamentous bacterium of 4–6 μm in
length, which grew only in L15 medium and Eagles MEM medium each supplemented with 10 % (v/v) foetal calf serum at 23–26 °C.
The human and animal pathology literature abounds with references to hard-toidentify or unidentifi ed pathogens. An example from fi sh pathology concerns a hitherto unknown intracellular bacterial pathogen of farmed Atlantic salmon in Ireland
(Palmer et al. 1994 ). During 1992–1993 when the water temperature was 8–9 and
15–16 °C, fi sh became lethargic, swam close to the water surface, and displayed
loss of balance. Apart from an infestation of salmon lice, the fi sh revealed the presence of petechia or haemorrhagic areas on the abdominal walls, petechia on the
pyloric caeca and swim bladder, congestion of the kidney and spleen, splenomegaly,
and kidney swelling. The fore and hind guts contained white mucus. Some fi sh had
pale friable livers, pale spleens, visceral adhesions, and false membranes in the
peritoneum (Palmer et al. 1994 ). The intracellular Gram-negative cocco-bacilli
required serum or blood for growth, which was accomplished on 7 % (v/v) horse
blood agar and 10 % (v/v) foetal calf serum medium after 4–14 days incubation at
15 or 22 °C (Palmer et al. 1994 ).
The organism was linked tenuously to the Neisseriaceae and Pasteurellaceae.,
although the rickettsias may be an appropriate home. According to Palmer et al .
( 1994 ) infectivity was achieved by injecting cells into Atlantic salmon, which
became moribund after 6–10 days, and died within 30 days. Moribund fi sh disBox 11.15: Unknown Gram-Negative Organism of Palmer et al . ( 1994 )
Cultures produce small colonies of 0.3 mm in diameter after incubation aerobically for 10–14 days. Anaerobic incubation results in larger colonies of
0.6 mm in diameter. Improved growth results by the addition of 0.5 mg of
L-cysteine hydrochloride/l. Colonies are off-white, convex and granular, and
contain non-motile, Gram-negative ß-haemolytic cocco-bacilli. Alkaline
phosphatase (weakly positive/variable), arginine dihydrolase, H 2 S (weakly
positive/variable), indole (weakly positive/variable) and lipases are produced,
but not α-glucosidase, N-acetyl glucosamine, catalase, ß-galactosidase,
ß-glucuronidase, lysine decarboxylase or oxidase. Nitrates are not reduced.
The Voges Proskauer reaction is negative. Neither aesculin, gelatin, Tween 80
nor urea is attacked. Citrate is not utilised. Fructose, glucose and maltose are
fermented, but not glycogen, lactose, mannitol, mannose, ribose, sucrose or
xylose. Growth occurs at 10 °C but not at 37 °C, and in 1–4 but not 5 % (w/v)
sodium chloride.
Unidentifi ed Gram-Negative Bacteria