A study of corynebacterial kidney disease of salmonid fishes

Graduation date: 1978This study was undertaken to compile a comprehensive\ud review of the literature and to gain a better understanding\ud of the host-parasite relationship in corynebacterial kidney\ud disease of salmonid fishes. An indirect fluorescent antibody\ud technique was developed which allowed differentiation\ud of intra- and extracellular bacteria. This technique was\ud used in combination with phase contrast microscopy to study\ud phagocytic interactions between salmonid cells and kidney\ud disease bacilli. Contrary to observations made at four to\ud five passages (Fryer, 1977), STE 137 cells (used from passages\ud 150 to 156) did not phagocytize the bacteria. Under\ud similar experimental conditions, the bacilli were avidly\ud phagocytized by mouse macrophages. Potential explanations\ud for the loss of phagocytosis in the STE 137 line were\ud explored.\ud Primary monolayer cell cultures from kidney and spleen,\ud and leucocyte cultures were established and grew well, but\ud failed to phagocytize the kidney disease bacillus. Differential\ud counts of blood films from normal, hatchery-raised,\ud 12.5 to 17.5 cm brook trout (Salvelinus fontinalis) showed:\ud 82.4 ± 0.9% lymphocytes, 12.1 ± 0.9% thrombocytes, 2.4 ±\ud 0.2% neutrophils, and 2.6 ± 0.3% blast forms.\ud The histopathology of corynebacterial kidney disease\ud was described by organ system (kidney, liver, pancreas,\ud gut, heart, gills, brain). The typical lesion was a distinct,\ud localized growth of bacteria and central mass of\ud amorphous, granular debris surrounded by a mixed, nonspecific\ud inflammatory response consisting of lymphocytes,\ud some degenerating neutrophils, and macrophages. Very few\ud polymorphonuclear leucocytes were observed. The lesions\ud are distinguished from the classic focal granulomas of\ud piscine tuberculosis or flavobacteriosis. The disease is\ud described as a "bacteremia characterized by a systemic,\ud diffuse...histiocytic inflammation" (Wolke, 1975).\ud The ultrastructure of the kidney disease bacterium and\ud its relationship to host tissues were studied via electron\ud microscopy. The mean length was 0.65 pm and the mean width\ud was 0.39 pm. The mean cell wall thickness was 16.1 nm and\ud the mean thickness of the cytoplasmic membrane was 8.8 nm