Identification Of Pathogens And Epidemiological Survey Of Bacteriosis Of Farmed Eriocheir Sinensis In Ponds

Eriocheir sinensis, known as Chinese Mitten Crab, is a kind of famous and precious freshwater crabs in China. Up to now, a variety of pathogens have been isolated from diseased E. sinensis, such as Aeromonas sp., Pseudomonas sp., Alcaligenes sp. Flavobacterium sp., Listonella sp., Vibrio sp., Bacillus sp., Pasteurlla sp., Myxobacteria sp., etc. They may cause many diseases to E. sinensis which include Ascitea Syndromes, Shell Ulcerative Disease, Trembling Disease, Edema Disease, Enteritis, Septic Infection Disease, Black Gill Diseases, Bad Leg Disease, Vibriosis, Liver Necrobacillosis, etc.These bacteriosis of E. sinensis are with sudden occurrence and high mortality which could cause great economic damage. With the purpose of figuring the cause of bacteriosis of E. sinensis out, recognizing the pathogenic species, and exploring the epidemic rule, the author has done the research. During April to October in2011and2012, we investigated many ponds in Xuanzhou District, Wuhu County, Wuwei County, Dangtu Country. The findings are as follows:1. Diseased E. Sinensis’ symptoms are soft-shell, horrible smell after opening the carapace, gill becoming grey black, with decayed mucus and ascites. Partial of their stomach and intestine are empty, and liver are fester. On the basis of the unusual status of the diseased E. sinensis and symptoms of the above, we can draw a conclusion that the common bacteriosis of these farmed E. sinensis are Ascitea Syndromes, Shell Ulcerative Disease, Black Gill Diseases, Liver Necrobacillosis, etc.2. Thirty-five strains of bacteria are isolated from the liver tissue and muscle tissue of the diseased E. sinensis. By artificial regression infection test, it is confirmed that the strains of DT9and WH21which come from Dangtu County and Wuhu County are pathogens. The infected Eriochheir sinensis’s liver tissue intersperses with creamy white mash, coelarium contains few ascites with strongly smell, presenting symptom of Liver Necrobacillosis. It is proved that the bacteria can cause the health crab infected and dead through artificial infecting tests and the mortality is100%in24hours. The symptom is identical with that in natural condition.3. The colony of pathogens on the solid media has the symbols of slight yellow, round (diameter range from2mm to2.5mm), central bulge, sharp edges, humid and smooth surface. The result of bacteria morphology inspection after gram stain is that they are G-bacillus, showing as dull circle, short but straight. Sometimes they are long filamentous in a disorderly array.4. The results of biochemical test for isolated strains are as following:their type of metabolism is ferment, oxidase positive; they can not grow in Sodium Chloride Broth (6%), have drug resistance to0/129agent, ferment glucose and produce acid and gas. We draw the conclusions that the strain DT9is A. Veronii and the strain WH21is A. Hydrophila from the eight measures for identifying the species of A. sp.(arginine decarboxylase, lysine decarboxylase, orinithine decarboxylase, esculoside, V-P, mannitol, saccharose, arabinose),5. Using the DNA from two stains of pathogens as PCR template, to amplify the16S rRNA genes, we get a DNA sequence about1500bp in length. The result of16S rRNA gene analysis is that both two amplification gene sequence are1,443bp long. DT9is most closely related to A. veronii (A. veronii, FJ490063) with homology being99.2%, and WH21is most closely related to A. hydrophila (A. hydrophila, AB680307) with homology being99.9%. By comprehensive analysis of the morphological characteristics,16S rRNA gene analysis and phylogenetic analysis of pathogens, we confirm that stain DT9is A. veronii, stain WH21is A. hydrophila.6. The result of antibiotic sensitivity test is that both stain DT9and stain WH21are sensitive, in various degrees, to Floxacin, Florfenicol, Colistin sulfate B, Amikacin, Gentamicin, Tobramycin, Kanamycin.7. The bacteriosis of E. sinensis in Anhui Province mainly include Ascitea Syndromes, Shell Ulcerative Disease, Black Gill Diseases, and Liver Necrobacillosis. They appear sporadically in April ever year. Then the morbidity rises from month by month, and peaks in August. A significant reduction in morbidity comes untill September, and it will disappear in October.