Cell wall chemistry, deoxyribonucleic acid base composition and pathogenesis of the kidney disease bacterium in salmonid fishes

Graduation date: 1979Experiments were designed to more precisely evaluate the effects of water temperature on the progress of bacterial kidney disease ( BKD) in three species of salmonid fishes. Infections were produced by intraperitoneal injection of suspensions of the causative organism into fish held at seven temperatures ranging from 3.9 to 20.5°C. Mortality was highest ( 78-100 percent) in coho salmon (Oncorhnchus kisutch) and steelhead trout (Salmo gairdneri) in the range of 6. 7 to 12.2 °C. At temperatures above 12.2 °C mortality decreased progressively to 8-14 percent at 20.5°C. In sockeye salmon (Oncorhynchus nerka) the suppressing effect on the disease process at these higher temperatures was, not apparent and mortality was essentially 100 percent at all temperatures from 6.7 to 20.5°C. Water temperature also influenced the mean number of days between infection and death. The interval was shortest in all three species at the higher temperatures, varying from 21 to 34 days at 15.0 to 20.5°C. As the temperature decreased the mean time to death increased progressively; at 6. 7 °C it varied from 60 to 71 days. To obtain data useful in further determining the taxonomic identification of the kidney disease bacterium (KDB) several biochemical characteristics of this organism were determined. The percent guanine plus cytosine in deoxyribonucleic acid from KDB was found to be 53.00 + 0.46 (95 percent confidence interval). Amino acid analysis of purified cell walls of KDB indicated that glutamic acid, lysine and glycine were present in equimolar concentrations. The principal sugars detected by gas-liquid chromatographic analysis of KDB cell wall hydrolyzates were glucose, arabinose, mannose and rhamnose. These results indicated the percent guanine plus cytosine was similar to that of species belonging to the genus Corynebacterium, however, the cell wall composition of the KDB isolates was markedly different from the type species of this genus. The biochemical properties reported here together with those of previous investigators indicate the existence of a bacterium sufficiently different from any other coryneform so as to be considered a new species. The KDB has only been isolated from species of fish in the subfamily Salmoninae, the salmon, trout and char, of the family Salmonidae. This limited host range supports the proposal of the name Corynebacterium salmoninus sp. nov. for KDB