DEVELOPING A MODEL FOR BACTERIAL KIDNEY DISEASE IN THE ZEBRAFISH, DANIO RERIO

DEVELOPING A MODEL FOR BACTERIAL KIDNEY DISEASE IN THE ZEBRAFISH, DANIO RERIO.

By Veronica Hulbig

Thesis Advisor: Dr. Ian Bricknell

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Marine Biology)

August, 2010

Bacterial kidney disease (BKD), caused by the bacterium Renibacterium salmoninarum, is a major disease threat to wild and cultured salmonids. The diseaseis extremely difficult to control, information regarding the pathogen is incomplete, and there is no effective treatment. Salmon and trout are the natural host of R. salmoninarum, but it is challenging and costly to work with these animals in the laboratory. Zebrafish have become an important tool in which to study development, normal body function, and disease. A zebrafish model for BKD would provide a tool to study the pathogenesis of R. salmoninarum. A better understanding of how the pathogen infects host cells could lead to better preventative treatments and vaccines for the disease. A zebrafish cell culture line was infected with R. salmoninarum to determine whether or not the bacterium is capable of infecting zebrafish cells. Zebrafish liver cells were acclimated to 15-, 22-, or 26 °C and inoculated with bacteria every hour, for 8 hours. R. salmoninarum was able to successfully infect zebrafish cells at room temperature at 8 h. Adult zebrafish were challenged with R. salmoninarum by injection method and left for 12 weeks. Fish were sampled every 2 weeks for confirmation by culture, immunofluorescence, histology, and PCR. The first group of fish was challenged with varying doses of R. salmoninarum to determine the median lethal dose. No fish died of R. salmoninarum and a disease response curve could not be determined. Some liver, spleen, and kidney tissues came back positive for R. salmoninarum via immunofluorescence. Based on these results, another group of fish was inoculated with a low and high dose of R. salmoninarum to evaluate progression of the disease in vivo. One fish was suspicious for R. salmoninarum by immunofluorescence, but all samples were negative via PCR and culture.Gram-positive bacteria were found in normally sterile organs and organs had mild to severe damage. This is the first time the zebrafish has been evaluated as a model for BKD and modifications to methods used in this study could lead to an effective model for BKD.