The ELISA technique has also been assessed for its effectiveness in the

The elisa technique has also been assessed for its

This preview shows page 282 - 284 out of 594 pages.

The ELISA technique has also been assessed for its effectiveness in the detection of carrier fish. Rose et al. (1989) compared a commercial ELISA kit (obtained from Stirling Diagnostics Ltd.), the commonly used corticosteroid/heat protocol of McCarthy (1980) and plating of rectum and kidney samples from Atlantic salmon onto BHIA and TSA. The Atlantic salmon were obtained from a site where out- breaks of furunculosis had previously occurred. From the results, it was apparent that the ELISA was the most successful technique, with 56.17% (14/26) of the fish shown to be carriers. This compared with a carrier rate of 26.4% as determined by means of the corticosteroid/heat test. Yet, plating techniques failed to reveal Aer. salmonicida in any of the fish. However, some disadvantages of ELISA are apparent, namely the inability to distinguish living from dead cells, and, for that matter, to differentiate viable, pathogenic cells from those resulting from use of living, attenu- ated or dead, virulent cells from vaccines. Moreover, ELISA does not enable the provision of cultures which could be used for additional investigation, such as the determination of antibiogrammes. Notwithstanding such drawbacks, ELISA is a valuable tool for the rapid detection of Aer. salmonicida in clinically diseased and asymptomatic carrier fish. It has not been conclusively established which organs of carrier fish serve as the site of carriage. From experiments using immunofluorescence techniques, Klontz (1968) concluded that the intestine is a primary site of infection, leading to the establishment of asymptomatic carriers. There is also some evidence to suggest that
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Epizootiology: Gram-negative bacteria 263 the kidney is involved, but the intestinal tract has again been mentioned (McCarthy, 1980). This is a subject which requires further work to clarify it. Another problematic aspect of the carrier state is that antibiotic therapy to control furunculosis outbreaks does not necessarily completely remove the bacterium from the tissues of fish, at least when sulphamerazine, furazolidone and potentiated sulphonamide are used. McCarthy (1980), however, reported that fish treated with tetracycline hydrochloride (i.m. injection of 50mg/kg) survived attempts to induce the disease. On the basis of such findings, McCarthy (1980) warned that it must be anticipated that fish populations treated for furunculosis will remain carriers. However, more recently other antibacterial compounds have been investigated for their ability to reduce or eliminate the carrier state of Aer. salmonicida in fish. Examples include erythromycin phosphate (Roberts, 1980), flumequine and an aryl-fluoroquinolone (Scallen and Smith, 1985) in combination with 0.01% Tween 80 to enhance the assimilation of the antimicrobial compound into fish (Markwardt et al, 1989). The last-mentioned group of workers found that the aryl- fluoroquinolone/surfactant combination was effective in eliminating the asympto- matic carrier state of Aer. salmonicida within 48 h of treatment. Markwardt and
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  • Bacteria, representative, gram-negative bacteria

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