Studies On Edwardsiellosis In Carassius Auratus Gibelio

Carassius auratus gibelio has the characteristics of fast growth,large individual,strong resistance and so on,and it shows good economic benefit in aquaculture production.The development of intensive farming lead to deterioration of the water environment,at the same time,farmers awareness of disease prevention and control are weak,leading to frequent aquatic disease.In 2015,the Shanghai Binhai base of C.auratus gibelio occurred hemorrhagic septicemia.To explore pathogen,we investigated the epidemic disease situation.The pathogeny of the disease was confirmed based on the pathogens analysis and artificial challenge experiment;16S rRNA gene and housekeeping gene(gyrB and rpoB)was identified,the pathogen phylogenetic tree was established,and the physiological and biochemical identification of the strain was identified by the API-32 E bacterial identification system and Biolog system.The types and classification of pathogens were determined synthetically.The hepatopancreas,kidney,spleen,gill and intestine of the diseased fish were observed by artificial challenge experiment.the pathogens of urease,gelatinase,lipase,amylase and hemolysis were measured.According to the seven virulence reported sequences,the primers were designed for PCR amplification to study the pathogen virulence genes carrying.Finally,The drug susceptibility test and immunization control were carried out for the pathogen,which provided reference for the production practice.Investigations showed that C.auratus gibelio hemorrhagic septicemia occured in June to September,2015,the temperature of the onset of the culture water is 25-27 ?,site mortality rate was 20%-30%.The initial symptoms is to reduce food intake and motionless sank to the bottom;Then the condition becomes serious,manifested as systemic congestion,hemorrhage,abdominal swelling,abdominal scales base severe bleeding,fin congestion and even bleeding,swelling and anal bleeding and pus-like fluid flow.Yellow turbid ascites in the abdominal cavity,hepatopancretic congestion,muscle congestion and bleeding,showing a typical symptoms of bacterial sepsis;The pathogen GY 15 was separated from the dying C.auratus gibelio visceral,intraperitoneal injection infection and soaking infection could lead to C.auratus gibelio morbidity and mortality,intraperitoneal injection of the median lethal dose(LD50)was 4.26×105 CFU/mL,and symptoms of artificial infection was similar to clinical symptoms.Physiological and biochemical and molecular biology methods were used to identify GY 15 strains.The results of identification of API-32 E were E.tarda,the identification rate was 99.8%,and the identification was excellent.The difference between the Biolog identification and E.tarda was 6.381,the similarity was 0.569,and the results of identification were well obtained.The results of the phylogenetic tree based on the molecular biology(16S rRNA gene and multiple sequence typing)were clustered with E.tarda.Based on the above results,the GY 15 strain was identified as E.tarda.The GY 15 strain is a new pathogen which caused C.auratus gibelio hemorrhagic sepsis,which is a new potential threat to carp's breeding.Artificial challenge experimentArtificial infection of C.auratus gibelio in the hepatopancreas,kidney and spleen showed the most serious pathological changes.Hepatopancreas mainly appeared cell swelling,vacuolar degeneration and cell necrosis;Kidney mainly manifested as renal parenchymal cell necrosis,inflammatory cell infiltration;Spleen tissue mainly showed a large number of hemoglobin pigmentation,cell necrosis and inflammatory cell infiltration phenomenon;Gill tissue mainly showed gill small pieces of epithelial cells,column cell swelling and bleeding symptoms;Pathological damage of intestinal tissue is minimal.The GY 15 strain was negative to urease,gelatinase,lipase,amylase and hemolysis.While,Seven virulence genes could be detected in GY 15 strain,which were sodB(490 bp),katB(377 bp),esrB(454 bp),gadB(308 bp),fimA(839 bp),citC(553 bp)and mukF(303 bp).Therefore,the GY 15 is a highly toxic strain.Comprehensive domestic isolated E.tarda virulence genes carrying case,It is believed that fimA and / or gadB genes coule be used to rapidly identify pathogenic E.tarda.Immunization and drug susceptibility were tested to explore the prevention and treatment of Edwardsiosis.Injection of inactivated vaccine and inactivated vaccine adjuvants can increase improve serum superoxide dismutase activity(SOD)and lysozyme activity activity(LZM),The immunization rates of inactivated and inactivated adjuvant vaccines against allogynogenetic crucian carp were 26.18% and30.42%,respectively,and did not achieve good immunoprotective effect.Antibioticsensitivity test showed that among 35 antibiotics tested,the GY 15 was sensitive to 26 kinds of antibiotics such as enrofloxacin,florfenicol and ofloxacin,but was resistant to 18 kinds of antibiotics such as neomycin,acheomycin and cotrimoxazole.It is recommended to use enrofloxacin,florfenicol,ciprofloxacin and norfloxacin for treatment in breeding.