Rapid Identification of Pathogenic Fich Bacteria

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The API ZYM system was used to identify the bacterial fish pathogens. As additional test, Gram stain and the activities of cytochrome oxidase and catalase were examined. The results of API ZYM and the additional tests were coded for easy identification.Various diagnostic methods used to detect Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD) , were compared. The most sensitive method was the enzyme immunoassay, which could detect 10^2 bacterial cells per gram of kidney tissue. The minimum bacteria concentrations showing posotive reactions to the indirect fluorescent antibody test (IFAT) and the coagglutination test were 10^3 and 10^4 cells/g kidney, respectively. The sensitivities of the Gram stain, immunodiffusion procedure, and latex agglutination test were low, and these methods could only be applied to fish with overt BKD symptoms. Altogether, 656 coho salmon Oncorhynchus kisutch were examined for R.salmoninarum antigen with the direct and indirect dot blot assays (DDBA and IDBA) and the IFAT.Among the fish sampled, positive reactions were obtained in 11.8% by the DDBA, 28.2% by the IDBA, and 12.9% by the IFAT.