Again interference could result from the presence of other morphologically

Again interference could result from the presence of

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Again, interference could result from the presence of other morphologically similar glycogen-containing bacteria. The early spate of interest in culturing techniques improved diagnosis, but the effectiveness was marred by the apparently slow growth of the organisms, i.e. up to 6 weeks at 15°C. In fact, recent evidence suggests that 19 weeks may be necessary for the initial incubation period. Therefore, there was widespread attention focused on
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Diagnosis 201 serological procedures as being the saviour of diagnosticians. This view has been reinforced by the current emphasis on western blots (e.g. Lovely et ai, 1994). But, which is more efficient—culturing or serology—at detecting renibacterium? Compar- ing kidney and ovarian fluid from broodstock Atlantic salmon, the selective medium, SKDM (see Austin et al, 1983a) detected a higher number of positive BKD samples than iFAT, which in turn was more sensitive than ELISA or western blots (Griffiths et ai, 1996). Interestingly, renibacteria were found in either kidney or ovarian fluid, but not both. However, the use of culturing in SKDM broth followed by western blotting increased the sensitivity beyond the maximum level recorded by SKDM alone (Griffiths et al, 1996). This is interesting because the benefit of this broth stage in increasing the detection rate for renibacterium paralleled an observation with peptone water during the 1970s. Here, we found that pre-incubation of kidney, spleen and more importantly heart tissue in peptone water enhanced the level of resulting colonies, and therefore positivity, on soHd medium. Another study concluded that ELISA, using a polyclonal rather than a monoclonal [this was less sensitive] anti- serum, was more sensitive than SKDM. Here, SKDM detected Ren. salmoninarum in 45% of kidney samples, compared with ELISA, which found that 50% of the kidneys were positive (Jansson et ai, 1996). A special case— Piscirickettsia salmonis Isolation in cell culture or detection in acridine orange stained smears or by iFAT has been advocated (Lannan and Fryer, 1991; Lannan et ai, 1991). IDENTIFICATION OF BACTERIAL ISOLATES The most common shortcomings in diagnosis of fish diseases concern the identifica- tion of bacterial isolates. There are two schools of thought, namely those that rely on serology and those relying on phenotypic tests. SEROLOGY We will preface further discussion by wholeheartedly endorsing a view that reliable diagnoses occur only with monospecific 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 defined reagents (GoerHch et al. 1984), and enhanced the rehabihty 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 not been adequately determined. Goerlich et al.
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  • Bacteria, representative, gram-negative bacteria

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