Study On Biochemical Activity And Pathogenicity Of Extracellular Products Of Aeromonas Caviae Isolated From Silurus Meriaionalis Chen

Ulcer syndrome Of Silurus meriaionalis Chen(S.meriaionalis Chen)is a bacterial infectious acute and lethal disease to the breed Silurus meriaionalis Chen in recently.The characteristics of the desease were quick infecting,high morbility and high death rate.The characteristic pathological changes contained ulcer of body surface,hepatomegalia, renomegaly,enlarged spleen,ascites,hyperemia and hemorrhage of gastrointestinal tract. The desease caused serious economic lost to breed the S.meriaionalis Chen our country. The aim of this investigation was to make the biochemical activity of extracellular products clear and to study the pathogenicity of the extracellular products to rice and S.meriaionalis Chen.The haemolysin was partially segregated and purified from the culture solution of by ammonium sulfate,DEAE- Sephadex A50 fast flow.The main methods and results were as follows:(1) The enzymatic activity and hemolytic activity of extracellular products of Aeromonas caviae isolated from S.meriaionalis Chen were determined by agar diffusion method and detected cytotoxicity by microamount board method.The results showed that the extracellular products ability to producted protease,lipase,gelatinase, urease,haemolysins and cytotoxins.(2) The pathology of mice infected with Aeromonas caviae extracellular products were studied by clinical and histopathology examination.The results showed that the extracellular products displayed lethality to mice,with a LD₅₀ value of 1.70mg/kg.The injected mice showed anhelation,energy languor,decreased food appetite,lungs hemorrhages,dilatation and tenuate of the intestinal wall,massive yellow phlegm in the cavum intestinale.Histopathological examination showed that the cardiac muscle fibers had degeneration and transverse striation disappearance;the angiotelectasis had anapetia and hemorrhage;some carcoplasm had clotting.Vacuolar degeneration appeared in liver the renal interstitium had widen,edema calidum and cell dissociation.;histoleucocyte and neutrocyte had effusion.Nephric tubule was stagnant blood,and acinus renis had congestion;The lymphocyte reduced and It appeared hemorrhage in spleen;the epithelium of pulmonary alveolus happened necrosis and exfoliation,lung accent appeared generous red blood cell in lungs.The epithelium of intestines showed necrosis and fell off.(3) The pathology of Silurus meriaionalis Chen infected with Aeromonas caviae extracellular product by pro inj intrams.The results showed that the extracellular products displayed lethality to Silurus meriaionalis Chen,with a LD₅₀ value of 0.802mg/kg and contained ulcer of body surface,ascites,hepatomegalia,renomegaly,enlarged spleen, ascites,hyperemia and hemorrhage of gastrointestinal tract.After injected intramuscularly with the ECP,the experimental fish showed obvious histopathological changes:The skeletal muscle and cardiac muscle had necrosis,fragmentation and inflammatory cell infiltration;The hepatic cell had a serious vacuolar degenemouseion;The nephric tubule had degenemouseion,necrosis and inflammatory cell infiltration between interstitial substance the spleen had splenemia,hemorrhage and lymphocytopenia;The Intestinal mucosa had necrosis and felling down.。The main Organs of disease fish were acutely damaged.Cytopathological changes showed that the cell swelled and the ultramicrostmcture destroyed.The muscle fiber had necrosis;the hepatic cell had a serious vacuolar degenemouseion,bioblast swelling and chromatin collecting;the cellula epithelialis had necrosis and leukocytic infiltrate.The blood biochemical and physiological indices were determined by Hitachi automatic intrument.The results showed that the number of red blood cells and protein in diseased fish remarkably compared with healthy fish,meanwhile the number of white cells,erythrocyte fragility,creatinine and serum enzymes of AST,ALT,LDH and Cr increased.(4) A hemolysin was partially purified from the culture solution of Aeromonas caviae by ammonium sulfate,DEAE -Sephadex A50 fast flow.The result showed that the molecular weight of the purified protease from Silurus meriaionalis Chen by SDS-PAGE was 32.2KD.It displayed pathogeof bone marrow,giant cellscity to S.meriaionalis Chen, The characteristic pathological changes contained abdomen intumescence,ascites,LSK intumescence and haemorrhage;There was massive yellow phlegm in the cavum intestinale.Histopathological examination showed the skeletal muscle was myoedema, degenemouseion and had necrosis of muscle fiber.The hepatic cell had degeneration, necrosis,blood sinus broaden and congestion.The renal tubular epithelial cell had degenemouseion,necrosis and inflammatory cell infiltration between interstitial substances.The spleen had splenemia,hemorrhage and homeocyte death the epithelium mucosae of stomach and intestine appeared necrosis and felling off.