94
Serology An immunodiffusion test for BKD, based on the detection of soluble
antigens in infected tissues, was developed by Chen et al. ( 1974 ) and discussed
further by Kimura et al. ( 1978 ). Use of this method together with more classical
agglutination reactions on ten isolates led to the conclusion by Bullock et al. ( 1974 )
that the causal agent of BKD was antigenically homogeneous. Following examination of over 50 isolates, we concur with this conclusion. Immunodiffusion was, of
course, much quicker than cultivation, with diagnosis, achieved on the basis of specifi c precipitin lines, taking no more than 24 h.
The co-agglutination test of Kimura and Yoshimizu (1981) showed considerable
promise for rapid detection of BKD, i.e. within 2 h. The anti- Renibacterium antibody coated staphylococcal cells are reacted with the supernatant from heated (i.e.
100 °C for 30 min) kidney tissues. Unlike iFAT/FAT, it does not require an expensive fl uorescence microscope, and would, therefore, be more suited to fi eld
conditions.
iFAT (Bullock and Stuckey 1975 ; Mitchum et al. 1979 ; Paterson et al. 1979 ;
Laidler 1980 ) and FAT (Bullock et al. 1980 ) have been developed for the diagnosis
of BKD. Improvements in the FAT included a 60 min staining time with the fl uorescent antibody (Cvitanich 1994 ). A further refi nement involved concentrating samples - in this case coelomic fl uid from spawning chinook salmon - on membrane
fi lters, which were used with FAT (Elliott and McKubben 1997 ). This modifi cation
was regarded as more sensitive than FAT on smears (Elliott and McKubben 1997 ).
iFAT has found use for detecting asymptomatic or overt cases of BKD (Bullock and
Stuckey 1975 ; Lee and Gordon 1987 ), although the technique is not always as sensitive and reliable as culturing (Armstrong et al. 1989 ). Indeed, Paterson et al. ( 1979 )
pointed to the enzootic nature of BKD in one Canadian river. These workers reported
asymptomatic infections in 33.4 % of 456 Atlantic salmon parr and 35.1 % of 37
adult salmon in the Margaree River. Seemingly, iFAT was more sensitive than the
examination of Gram-stained kidney tissue or cultivation on Mueller-Hinton agar
supplemented with 10 % foetal calf serum and 0.1 % L-cysteine hydrochloride
(Paterson et al. 1979 ). A view has been expressed about the value of western blots
(e.g. Lovely et al. 1994 ). But which is more effi cient at detecting renibacterium,
culturing or serology? Hsu et al. ( 1991 ) described a monoclonal antibody based
ELISA which appears to be effective for the diagnosis of BKD. This system detected
0.05–0.1 μg of antigen/ml within a few hours.
The developments of serological methods for the detection and/or diagnosis of
BKD must be examined sceptically because the reports preceded detailed taxonomic study of the organisms. It is unclear how workers knew that the aetiological
agent possessed a unique antigenic profi le, distinguishing it from other Grampositive organisms. Unfortunately, the reliability of serological methods may now
be questioned insofar as cross-reactions with apparently unrelated organisms have
been recognised. Bullock et al. ( 1980 ) observed large bacteria, in faecal samples of
brook trout, which fl uoresced with antiserum to Renibacterium . After studying
authentic representatives of 44 Gram-positive bacterial taxa and 101 cultures from
fi sh and water, Austin and Rayment ( 1985 ) reported false positive reactions with
3 Aerobic Gram-Positive Rods and Cocci
Serology An immunodiffusion test for BKD, based on the detection of soluble
antigens in infected tissues, was developed by Chen et al. ( 1974 ) and discussed
further by Kimura et al. ( 1978 ). Use of this method together with more classical
agglutination reactions on ten isolates led to the conclusion by Bullock et al. ( 1974 )
that the causal agent of BKD was antigenically homogeneous. Following examination of over 50 isolates, we concur with this conclusion. Immunodiffusion was, of
course, much quicker than cultivation, with diagnosis, achieved on the basis of specifi c precipitin lines, taking no more than 24 h.
The co-agglutination test of Kimura and Yoshimizu (1981) showed considerable
promise for rapid detection of BKD, i.e. within 2 h. The anti- Renibacterium antibody coated staphylococcal cells are reacted with the supernatant from heated (i.e.
100 °C for 30 min) kidney tissues. Unlike iFAT/FAT, it does not require an expensive fl uorescence microscope, and would, therefore, be more suited to fi eld
conditions.
iFAT (Bullock and Stuckey 1975 ; Mitchum et al. 1979 ; Paterson et al. 1979 ;
Laidler 1980 ) and FAT (Bullock et al. 1980 ) have been developed for the diagnosis
of BKD. Improvements in the FAT included a 60 min staining time with the fl uorescent antibody (Cvitanich 1994 ). A further refi nement involved concentrating samples - in this case coelomic fl uid from spawning chinook salmon - on membrane
fi lters, which were used with FAT (Elliott and McKubben 1997 ). This modifi cation
was regarded as more sensitive than FAT on smears (Elliott and McKubben 1997 ).
iFAT has found use for detecting asymptomatic or overt cases of BKD (Bullock and
Stuckey 1975 ; Lee and Gordon 1987 ), although the technique is not always as sensitive and reliable as culturing (Armstrong et al. 1989 ). Indeed, Paterson et al. ( 1979 )
pointed to the enzootic nature of BKD in one Canadian river. These workers reported
asymptomatic infections in 33.4 % of 456 Atlantic salmon parr and 35.1 % of 37
adult salmon in the Margaree River. Seemingly, iFAT was more sensitive than the
examination of Gram-stained kidney tissue or cultivation on Mueller-Hinton agar
supplemented with 10 % foetal calf serum and 0.1 % L-cysteine hydrochloride
(Paterson et al. 1979 ). A view has been expressed about the value of western blots
(e.g. Lovely et al. 1994 ). But which is more effi cient at detecting renibacterium,
culturing or serology? Hsu et al. ( 1991 ) described a monoclonal antibody based
ELISA which appears to be effective for the diagnosis of BKD. This system detected
0.05–0.1 μg of antigen/ml within a few hours.
The developments of serological methods for the detection and/or diagnosis of
BKD must be examined sceptically because the reports preceded detailed taxonomic study of the organisms. It is unclear how workers knew that the aetiological
agent possessed a unique antigenic profi le, distinguishing it from other Grampositive organisms. Unfortunately, the reliability of serological methods may now
be questioned insofar as cross-reactions with apparently unrelated organisms have
been recognised. Bullock et al. ( 1980 ) observed large bacteria, in faecal samples of
brook trout, which fl uoresced with antiserum to Renibacterium . After studying
authentic representatives of 44 Gram-positive bacterial taxa and 101 cultures from
fi sh and water, Austin and Rayment ( 1985 ) reported false positive reactions with
3 Aerobic Gram-Positive Rods and Cocci