Edwardsiella Ictaluri: Pathogenic Mechanisms and Antigens Recognized by Infected Channel Catfish.
Date of Award
Doctor of Philosophy (PhD)
Joseph C. Newton
To clarify early events in the pathogenesis of enteric septicemia of catfish, 140 channel catfish fingerlings (Ictalurus punctatus) were each infected with approximately 1.0 $\times$ 10$\sp9$ colony forming units Edwardsiella ictaluri (E. ictaluri) by intragastric intubation. Fish were sacrificed at 0, 0.25, 0.5, 1, 3, 6, 12, 24, 48, 72, 96, and 120 hours post infection (PI). Multiple tissue samples were evaluated by gross observation, light and electron microscopy, and immunohistochemical methods. In addition, stomach, intestine, trunk kidney, and liver were cultured quantitatively for bacteria. Trunk kidney cultures were positive by 0.25 hours PI, indicating rapid transmucosal passage. Histologic lesions were evident in the intestine at 0.5 hours PI and in other tissues at 48 hours. In the intestine, E. ictaluri was seen in contact with the brush border at 0.5 hours PI. Also at 0.5 hours PI, dilated cells with large intracytoplasmic inclusions were observed subadjacent to the basement membrane. From 1 to 3 hours PI, occasional necrotic enterocytes were seen on tips of intestinal folds. Proprial leukocytes were rare before 24 hours PI but common thereafter, and many contained cytoplasmic bacteria. In other tissues, earliest observed lesions (48 hours PI) consisted of bacteria within vascular associated phagocytic cells. Electron microscopy showed bacteria were in cytoplasmic vacuoles within phagocytes. Bacteria were also seen within vacuoles in enterocytes and hepatocytes at later time periods. This study confirms E. ictaluri can invade channel catfish by crossing the intestinal mucosa and suggests E. ictaluri may have a similar pathogenesis as other enteroinvasive enterobacteriaceae. In addition, antigens of E. ictaluri recognized by channel catfish infected naturally were determined by probing bacterial components with serum from diseased fish. Whole cell preparations and enriched fractions of outer membrane proteins, flagella, and lipopolysaccharide (LPS) were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and transferred to nitrocellulose membranes. Transfer was verified by India ink staining. Separated bacterial components affixed to nitrocellulose membranes were probed using catfish serum and catfish serum absorbed with purified LPS. Lipopolysaccharide and the major outer membrane protein (37 kD) were strongly immunogenic. A flagellar antigen (36 kD) and five additional outer membrane proteins (51 kD, 39 kD, 33 kD, 23.5 kD and 21 kD) were weakly immunogenic.
Baldwin, Thomas James, "Edwardsiella Ictaluri: Pathogenic Mechanisms and Antigens Recognized by Infected Channel Catfish." (1992). LSU Historical Dissertations and Theses. 5421.