Identification Of Causative Pathogen For Visceral White-spot And Histopathologic Research On Pseudosciaena Crocea

In recent years, a serious disease occurred in cage culture Pseudosciaena crocea ofXiangshan, east coast of Zhejiang province in China,which resulted in significant economiclosses and threated to the healthe of Pseudosciaena crocea aquaculture farming. As researchedobject to white-spot disease, the cause of disease, histopatholygy and ultrapathology have beenstudied and the purpose is to find out the disease pathogens and pathogenesis, for aquacultureproduction to effectively diagnose and provide a scientific basis for disease prevention andcontrol.A pathogenic bacterium (XSDHY-P) was isolated from spleen of naturally diseasedPseudosciaena crocea. After artificial infection experiments as a pathogen of Pseudosciaenacrocea ulcer disease. The bacterium,s morphology and physiology analysis showed that thebacterium was gramnegative, movement, no capsular and no capsule, polar flagella. Combinephysiological and biochemical analysis with16S rRNA sequence analyzed and phylogeneticdendrogram was constructed, the results showed that the bacteria XSDHY-P has a closingphylogenetic relation to Pseudomonas plecoglossicida. Drug sensitivity experiments showedthat the bacteria is sensitive to doxycycline, tetracycline, gentamicine and insensitive toampicillin, chloramphenicol. Mesured the MIC and the MBC of5drugs, including tetracycline,norfloxacin and et.al, the results showed that5drugs have strong bactericidal effect and MICare equal or times to MBC. Most durgs used in combination can enhance effect of antibacterialexpect gentamicin and tetracycline. The research on the growth property of strain XSDHY-Pindicated that it grows better in the temperature range from28℃t o37℃, pH from6.5to9.0,salinity from0to25‰.The pathogenicity of Pseudosciaena crocea infected Pseudomonas plecoglossicida wasevaluated through microscope and election microscope. Histopathological examination showeddegeneration and necrotic changes in many organs. Liver, spleen and kidney, as target organs ofinfection, appeared metamorphic necrosis. Further, vacuolization serious, inflammatory cellinfiltration and pathological nodules were evident. Cytopathological changes showed swellingand ultrastructure destroy in visceral cells of liver, spleen, kidney. The mitochondria swelled, dissolution of the cristaes and the chromatin showed condensation and margination. Largenumbers of pathogenic bacteria geathered in kidney and spleen.The histopathological changesin the diseased Pseudosciaena crocea may lead to the dysfunction of the organ which resultedin death.