Study On Biochemical Activity And Pathogenicity Of Extracellular Products Of Stenotrophomonas Maltophilia From Channel Catfish

Recently, The Stenotrophomonas maltophilia from Channel Catfish was detected as the pathogen of a acute epidemic of channel catfish(Ictalurus Punctatus) in China. The pathology of charmel catfish infected by Stenotrophomonas maltophilia showed many typical characters, like many irregular, variably sized areas of bianch in the body surface, distension of abdomen, enteritis and intussusceptions etc. However, the pathogenic mechanism of Stenotrophomonas maltophilia infection was unclear. The aim of this investigation was to make the biochemical activity of extracellular products clear, and to understand the pathogenicity of extracellular products to rice and channel catfish.The biologic activities of Stenotrophomonas maltophilia extracellular products were studied. The results showed that the extracellular products include amylase, lipase, protease, urease, haemlysin, cytotoxicity and cell toxicity.The pathology of mice infected with Stenotrophomonas maltophilia's extracellular products was studied by clinical and histopathology examination. The extracellular products displayed lethality to mice, with a LD₅₀ value of 5.37mg/kg。The main symptom was anhelation, mucous cenosis, lungs hemorrhages, dilatation and tenuate of the intestinal wall, massive mucous in the cavum intestinale. Histopathologieal examination showed blood capillary congested, the epithelium of pulmonary alveolus happened necrosis and exfoliation, lung accent appeared extravasated blood in lungs; epithelium of intestines happened necrosis, abscission; Vacuolar degeneration appeared in liver; cells of white pulp in spleen reduced, and red pulp appeared hemorrhage in spleen.The pathology of channel catfish infected with Stenotrophomonas maltophilia's extracellular products was studied by clinical, histopathology and microscope examination. The extracellular products displayed lethality to channel catfish, with a LD₅₀ value of 3.21 mg/kg。The main symptom showed that congestion and hemorrhage in the root of fins, and many irregular, variably sized areas of bianch in the body surface, distension of abdomen, and there may be bloody mucus and fluid in the cavum abdominis, enteritis and intussusceptions, hemorrhage in mucus of intestinal tract. Histopathological examination showed revealed that edema, vacuolar degeneration, even necrosis in live; hyperaemia, intumesce in glomcrulus; granular degeneration and vacuolar degeneration in the epithelia of nephric tubule; lymphocyte induced and hemorrhaged in spleen; swelling and necrosis in gill lamella epithelia; necrotizing myositis in skeletal muscles. Cytopathological changes showed that swelling and ultrastructure destory in visceral organs' cells. The chromatin showed condensation and margination. The mitochondria swelled with disintegration and lyses of the cristaes.