135
Pathogenicity
Koch’s Postulates were eventually fulfi lled using previously vaccinated fi sh which
were challenged via i.p. injection with 2 × 10
5 , 2 × 10
6 and 2 × 10
7 cells/fi sh (Olsen
et al. 2006b ).
Rhodococcus qingshengii
Characteristics of the Disease
A condition was recognised in Chilean Atlantic salmon during 2008 whereby there
were not any overt clinical signs of disease, but internally there was severe peritonitis with white, loose to compact pseudo-membranes [reddish-tan exudates were
noted sometimes on the internal organs, notably the heart, liver and spleen
(Avendaño-Herrera et al. 2011 )].
Isolation
Bacterial isolation was achieved using TSA supplemented with 1 % (w/v) NaCl and
Columbia sheep blood agar with incubation aerobically at 20 °C for 72 h (AvendañoHerrera et al. 2011 ).
Characteristics of the Pathogen
One isolate, 79043–3, was studied:
Box 3.21: Rhodococcus qingshengii
Colonies are off white, smooth and circular with regular edges, and contain
short non-motile, non-fermentative, Gram-positive cells that produce catalase
but not arginine dihydrolase, lysine or ornithine decarboxylase or oxidase.
Nitrates are reduced. The methyl red test is positive, but the Voges Proskauer
reaction is negative. Neither casein, DNA, gelatin, elastin, urea nor Tween 80
was degraded. Growth occurs at 15–37 °C and in 0–3 % (w/v) NaCl. Growth
does not occur on MacConkey agar or TCBS. With API 20STREP, positivity
is recorded to aesculin, 2-naphthyl-ß-D-galactopyranoside, 2-naphthyl phosphate and L-leucine-2-naphthylamide pyruvate. Using API ZYM, 2-naphthyl
phosphate, naphthol-AS-BI-phosphate, 2-naphthyl-α-D-glucopyranoside,
2-naphthyl caprylate, 6-Br-2-naphthyl-ß-D-glucopyranoside, L-leucyl-2naphthylamide and L-valyl-2-naphthylamide were utilised. The major fatty
acid methyl esters are C 16:0 (22.43 %), C 18:1 ω9c (24.48 %),10-methyl C 18:0
(13.13 %) and summed feature 3 (16.40 %; comprising C 16:1 ω6c/C 16:1 ω7c).
(Avendaño-Herrera et al. 2011 ).
Nocardiaceae Representatives
Pathogenicity
Koch’s Postulates were eventually fulfi lled using previously vaccinated fi sh which
were challenged via i.p. injection with 2 × 10
5 , 2 × 10
6 and 2 × 10
7 cells/fi sh (Olsen
et al. 2006b ).
Rhodococcus qingshengii
Characteristics of the Disease
A condition was recognised in Chilean Atlantic salmon during 2008 whereby there
were not any overt clinical signs of disease, but internally there was severe peritonitis with white, loose to compact pseudo-membranes [reddish-tan exudates were
noted sometimes on the internal organs, notably the heart, liver and spleen
(Avendaño-Herrera et al. 2011 )].
Isolation
Bacterial isolation was achieved using TSA supplemented with 1 % (w/v) NaCl and
Columbia sheep blood agar with incubation aerobically at 20 °C for 72 h (AvendañoHerrera et al. 2011 ).
Characteristics of the Pathogen
One isolate, 79043–3, was studied:
Box 3.21: Rhodococcus qingshengii
Colonies are off white, smooth and circular with regular edges, and contain
short non-motile, non-fermentative, Gram-positive cells that produce catalase
but not arginine dihydrolase, lysine or ornithine decarboxylase or oxidase.
Nitrates are reduced. The methyl red test is positive, but the Voges Proskauer
reaction is negative. Neither casein, DNA, gelatin, elastin, urea nor Tween 80
was degraded. Growth occurs at 15–37 °C and in 0–3 % (w/v) NaCl. Growth
does not occur on MacConkey agar or TCBS. With API 20STREP, positivity
is recorded to aesculin, 2-naphthyl-ß-D-galactopyranoside, 2-naphthyl phosphate and L-leucine-2-naphthylamide pyruvate. Using API ZYM, 2-naphthyl
phosphate, naphthol-AS-BI-phosphate, 2-naphthyl-α-D-glucopyranoside,
2-naphthyl caprylate, 6-Br-2-naphthyl-ß-D-glucopyranoside, L-leucyl-2naphthylamide and L-valyl-2-naphthylamide were utilised. The major fatty
acid methyl esters are C 16:0 (22.43 %), C 18:1 ω9c (24.48 %),10-methyl C 18:0
(13.13 %) and summed feature 3 (16.40 %; comprising C 16:1 ω6c/C 16:1 ω7c).
(Avendaño-Herrera et al. 2011 ).
Nocardiaceae Representatives