667
reaction and micromorphology of the pathogen. Possibilities include the presence
of Gram-positive or Gram-negative rods (spore-bearing or asporogenous), cocci
and mycelium. For Gram-positive organisms, the acid-fast stain will help in the
recognition of Mycobacterium, Nocardia , and possibly Rhodococcus.
Bacteriological Examination
Tissues to be Sampled
Generally, examination should be made of any damaged tissues. Experience has
taught us that it is always advisable to include a kidney sample, which often permits
the most satisfactory isolation of the pathogen. Quite simply it is adequate to sample
the material by means of swabbing, while minimizing the changes of contamination. The swabs should then quickly be used to inoculate the bacteriological media.
Identifi cation of Bacterial Isolates
The most common shortcomings in diagnosis of fi sh diseases concern the identifi cation of bacterial isolates. There are three schools of thought, namely those that rely
on serology, molecular techniques, and those relying on more conventional phenotypic tests.
Serology
We will preface further discussion by wholeheartedly endorsing a view that reliable
diagnoses occur only with monospecifi c antisera to assure the homologous reaction
between antigen and antibody. The development of monoclonal antibodies has
improved diagnoses by standardising serological tests, i.e. by means of defi ned
reagents (Goerlich et al . 1984 ), and enhanced the reliability of ELISA, iFAT and
immunohistology for the detection of pathogens, such as Mycobacterium spp. and
Ren. salmoninarum (Adams et al. 1995 ). In contrast, it may be argued that the more
conventional polyclonal antibodies have generated contradictory results. Also, the
extent of any cross-reactions with polyclonal antibodies has often not been adequately determined. Goerlich et al. ( 1984 ) noted that a monoclonal antibody raised
against a typical virulent isolate of Aer. salmonicida (i.e. the strain possessed an
A-layer) reacted only with virulent cultures, but not with avirulent cells (i.e. those
lacking an A-layer).
Bacteriological Examination
reaction and micromorphology of the pathogen. Possibilities include the presence
of Gram-positive or Gram-negative rods (spore-bearing or asporogenous), cocci
and mycelium. For Gram-positive organisms, the acid-fast stain will help in the
recognition of Mycobacterium, Nocardia , and possibly Rhodococcus.
Bacteriological Examination
Tissues to be Sampled
Generally, examination should be made of any damaged tissues. Experience has
taught us that it is always advisable to include a kidney sample, which often permits
the most satisfactory isolation of the pathogen. Quite simply it is adequate to sample
the material by means of swabbing, while minimizing the changes of contamination. The swabs should then quickly be used to inoculate the bacteriological media.
Identifi cation of Bacterial Isolates
The most common shortcomings in diagnosis of fi sh diseases concern the identifi cation of bacterial isolates. There are three schools of thought, namely those that rely
on serology, molecular techniques, and those relying on more conventional phenotypic tests.
Serology
We will preface further discussion by wholeheartedly endorsing a view that reliable
diagnoses occur only with monospecifi c antisera to assure the homologous reaction
between antigen and antibody. The development of monoclonal antibodies has
improved diagnoses by standardising serological tests, i.e. by means of defi ned
reagents (Goerlich et al . 1984 ), and enhanced the reliability of ELISA, iFAT and
immunohistology for the detection of pathogens, such as Mycobacterium spp. and
Ren. salmoninarum (Adams et al. 1995 ). In contrast, it may be argued that the more
conventional polyclonal antibodies have generated contradictory results. Also, the
extent of any cross-reactions with polyclonal antibodies has often not been adequately determined. Goerlich et al. ( 1984 ) noted that a monoclonal antibody raised
against a typical virulent isolate of Aer. salmonicida (i.e. the strain possessed an
A-layer) reacted only with virulent cultures, but not with avirulent cells (i.e. those
lacking an A-layer).
Bacteriological Examination