Study On Biochemical Activity And Pathogenicity Of Extracellular Products Of Aeromonas Veronii From Channel Catfish

Recently, the Aeromonas veronii from Channel Catfish was detected as the pathogen of an acute epidemic of channel catfish(Ictalurus Punctatus) in China. The pathology of channel catfish infected by A. veronii showed obvious symptoms, like abdomenal swelling, enteritis and hemorrhage in multiple organs. However, the pathogenic mechanism of A. veronii 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 channel catfish.The biologic activities of A. veronii extracellular products were studied. The results showed that the extracellular products included ipase, proteinase, lecithinase, DNAase and hemolysin. The spectrum of ECP hemolytic in various animal species red blood cells was determined with the methods discribed by Sabine W’s. The result indicated that the hemolytic effect of ECP on erythrocyte in chicken and duck were futile, but it had a high hemolytic activity against man, catfish, rabbit erythrocytes.The pathology of channel catfish infected with A.veronii’s extracellular products was studied by clinic and histopathology. The symptom and pathological changes of artifical infection were similar to nature disease. And A. veronii’s extracellular products displayed lethality to channel catfish. The main clinical pathological symptom:marked petechial hemorrhages and variably sized areas of bleaching spot of skin and congestion of internal organs, particularly in the liver, spleen and kidneys. Other features included rough of the surface spleen, enteritis and ascites. After24h of injected the ECPase, the channel catfish died. Histopathological examination showed oedema, degeneration and necrotic changes in many organs. Edema, vacuolar degeneration, even necrosis in liver, hemorrhage, even necrosis in heart, intumesce in glomcrulus. Vacuolar degeneration in the epithelia of nephric tubule. The spleen was hemorrhagic and reticuloendotheliosis hyperplasia, as will as lymphocyte decreased. Hemorrhage, neuronophagia phenomenon and neuronal degeneration were seen in brain. Haemorrhagia and necrosis in gill lamella epithelia.