136
By means of the API 20STREP data base, an identifi cation of Str. salivarius was
obtained. However, sequencing of the 16S rRNA gene led to the association with
the genus Rhodococcus , with the closest matches to Rhodococcus baikonurensis
GTG 1041 T, Rhodococcus erythropolis DSM 43066
T
, Rhodococcus jialingiae djl6–2 T and Rhodococcus qingshengii djl-6 T , and corresponding to sequence homologies of 99.47, 99.31, 99.79 and 99.79 %, respectively (Avendaño-Herrera et al.
2011 ). DNA:DNA hybridization revealed that 79043–3 showed 88.7 % reassociation with with Rhodococcus qingshengii , but only 61.0 % and 39.3 % homology Rhodococcus erythropolis and Rhodococcus baikonurensis , respectively. Of
relevance, a comparison of 79043–3 with rhodococci from diseased Norwegian and
Scottish Atlantic salmon (Olsen et al. 2006) revealed almost 99.8 % sequence
homology with the strains of Rhodococcus erythropolis 00/50/6670 and 4115, from
the previous study (Olsen et al. 2006). It is questionable whether there are two
pathogenic rhodococci, i.e. Rhodococcus erythropolis and Rhodococcus qingshengii or just one as seems likely from the data.
Pathogenicity
79043–3 caused mortalities within 3 days of experimental infections with Atlantic
salmon [60 % mortality with a dose of 5 x 10
7 CFU/fi sh] with disease signs including haemorrhages particularly around the eyes, mouth and opercula. Internally,
there was ascites, melanosis in the abdominal cavity, pale liver, splenomegaly, internal hemorrhaging, and the presence of pseudo-membranes on the heart, liver,
spleen, and swim bladder (Avendaño-Herrera et al. 2011 ).
Planococcaceae Representative
Planococcus sp.
Characteristics of the Disease
Since 1988, there has been a steady increase in the incidence of motile Grampositive cocci, tentative Planococcus, associated with diseases of Atlantic salmon
and rainbow trout in the UK. In some cases, it appeared that the Gram-positive cocci
were inhabiting fi sh that had previously received extensive chemotherapy to control
diseases caused by Gram-negative bacteria. The organism has been associated with
small off white (2–4 mm diameter) round recessed spots on the heads of Atlantic
salmon (Austin et al. 1988 ). In large rainbow trout (average weight = 500 g), the
only disease sign was the presence of watery kidney and small amounts of ascitic
fl uid in the peritoneal cavity (B. Austin, unpublished data). In addition during 1990,
the organism was associated with two populations of rainbow trout fry deemed to
3 Aerobic Gram-Positive Rods and Cocci
By means of the API 20STREP data base, an identifi cation of Str. salivarius was
obtained. However, sequencing of the 16S rRNA gene led to the association with
the genus Rhodococcus , with the closest matches to Rhodococcus baikonurensis
GTG 1041 T, Rhodococcus erythropolis DSM 43066
T
, Rhodococcus jialingiae djl6–2 T and Rhodococcus qingshengii djl-6 T , and corresponding to sequence homologies of 99.47, 99.31, 99.79 and 99.79 %, respectively (Avendaño-Herrera et al.
2011 ). DNA:DNA hybridization revealed that 79043–3 showed 88.7 % reassociation with with Rhodococcus qingshengii , but only 61.0 % and 39.3 % homology Rhodococcus erythropolis and Rhodococcus baikonurensis , respectively. Of
relevance, a comparison of 79043–3 with rhodococci from diseased Norwegian and
Scottish Atlantic salmon (Olsen et al. 2006) revealed almost 99.8 % sequence
homology with the strains of Rhodococcus erythropolis 00/50/6670 and 4115, from
the previous study (Olsen et al. 2006). It is questionable whether there are two
pathogenic rhodococci, i.e. Rhodococcus erythropolis and Rhodococcus qingshengii or just one as seems likely from the data.
Pathogenicity
79043–3 caused mortalities within 3 days of experimental infections with Atlantic
salmon [60 % mortality with a dose of 5 x 10
7 CFU/fi sh] with disease signs including haemorrhages particularly around the eyes, mouth and opercula. Internally,
there was ascites, melanosis in the abdominal cavity, pale liver, splenomegaly, internal hemorrhaging, and the presence of pseudo-membranes on the heart, liver,
spleen, and swim bladder (Avendaño-Herrera et al. 2011 ).
Planococcaceae Representative
Planococcus sp.
Characteristics of the Disease
Since 1988, there has been a steady increase in the incidence of motile Grampositive cocci, tentative Planococcus, associated with diseases of Atlantic salmon
and rainbow trout in the UK. In some cases, it appeared that the Gram-positive cocci
were inhabiting fi sh that had previously received extensive chemotherapy to control
diseases caused by Gram-negative bacteria. The organism has been associated with
small off white (2–4 mm diameter) round recessed spots on the heads of Atlantic
salmon (Austin et al. 1988 ). In large rainbow trout (average weight = 500 g), the
only disease sign was the presence of watery kidney and small amounts of ascitic
fl uid in the peritoneal cavity (B. Austin, unpublished data). In addition during 1990,
the organism was associated with two populations of rainbow trout fry deemed to
3 Aerobic Gram-Positive Rods and Cocci