Rapid Method for Detection of Bacterial Kidney Disease of Salmonid (BKD) by Coagglutination of Antibody Sensitized Protein A-Containing Staphylococci

Abstract

The application of a coagglutination test using staphylococci specifically sensitized with antibody against the bacterium causing bacterial kidney disease to the diagnosis of this disease in salmonids was studied. This method proved to be a simple, rapid and reliable diagnostic test suitable for use in the laboratory or field, and requires no special apparatus. It was found to be highly specific and more sensitive than the immunodiffusion test. In a study of 758 fish from 24 farms suspected in outbreaks of bacterial kidney disease the rate of detection of the disease with the coagglutination test was as high or highter than the rates obtained by Gram staining or clinical examination.
The procedure of this method is summarized as follows:
1) Kidney sample from diseased fish is homogenized with four to nine volumes of PBS, and heated in a boiling water bath for 30min.
2) The supernatant is collected after centrifugation at 4000 rpm for 20min. This may be omitted if a centrifuge is unavailable.
3) One drop of the supernatant and one drop of anti-BKD antibody sensitized staphylococci suspension are mixed on a glass slide and incubated at room temperature. The slide is examined after 30, 60 and 120min.
4) If positive coagglutination is observed, the infected fish should be examined microscopically to confirm the diagnostic results.