Pathogenesis of Enteric Septicemia of Channel Catfish, Caused byEdwardsiella ictaluri: Bacteriologic and Light and Electron Microscopic Findings

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Abstract
To clarify early events in the pathogenesis of enteric septicemia of catfish, 140 channel catfish Ictalurus punctatus (8–10 months old) were each infected with approximately 1.0 × 109 colony-forming units of Edwardsiella ictaluri by intragastric intubation. Fish were sacrificed at 0, 0.25, 0.5, 1, 3, 6, 12, 24, 48, 72, 96, and 120 h postinfection (PI). Multiple tissue samples at all scheduled sampling times were evaluated by gross observation, light and electron microscopy, and immunohistochemical methods. In addition, at each sampling time, stomach, intestine, trunk kidney, and liver were cultured to quantitate bacteria. Trunk kidney cultures were positive by 0.25 h PI, indicating rapid transmucosal passage. In the intestine, E. ictaluri was seen in contact with the brush border at 0.5 h PI. Also at 0.5 h PI, dilated basilar cells with large intracytoplasmic inclusions were observed adjacent to the basement membrane. From 1 to 3 h PI, occasional necrotic enterocytes were seen on tips of intestin...

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