Isolation And Identification Of Pathogenand Histop Athological Observation Of Ulcer In Schizothorax Prenanti

From December, 2005 to April, 2006, there had been an outbreak disease characterized as skin broken on one side dorsal fin and muscle ulcer of Schizothorax Prenanti in Yaan, Panzhihua and other regions, which had caused heavy economic losses. In order to figure out the pathogen and pathogenesis of the disease, the aetiology, pathology and virulence factors were studied.A pathogenic bacterium (D060501) was isolated fi'om the muscular and liver of the diseased fish. Artificial infection proved that the bacterium was the pathogen of the disease. Its morphological, physiological, biochemical characteristics and 16s rDNA sequence analysis were studied furthermore. The bacterium colony on the TSA medium showed edge slick and round white. When it had grown for 24h in cony blood, it formed diaphanousβ-zone of hemolysis. The bacteria was gram negative, rods, mobility-positive, lipase-positive, Oxidase-positive, arginine-diphydrolase-positive, altose-positive, potassium cyanine-positive, V-P-test-positive, H2S-negative, DNAase-negative, urea-negative. It. produced gas and acid by means of gluosa and arabinase, respectively. A 1591bp 16SRNA complementary fragment of D060501 was checked by amplification using bacteria general PCR primer. The sequence classifer in RDP Database suggested that it belonged to Aeromonas. A phylogenetic tree was constructed by comparing the 16SrRNA sepuences of the isolated strain(GenBank)with other relative bacteria species in the GenBank databases. The homology between strain D060501 and other Aeromonas hydrophila was 99.1%. According to phylogenetic analysis, the isolated strain(D060501) was identified as Aeromonas hydrophila.The toxicity of D060501 was studied by means of I. M., scuffing immerse and immerse test. The results showed that I. m. and scuffing immerse caused the similar skin ulcer and death. A pathogenic bacterium which showed similarity to D060501 in morphological, physiological and biochemical characteristics was also islated from the circum-musculus focus of infection and liver in artifical inffected fishes in the condition of asepsis. This indicated D060501 was the pathogenic bacterium of skin ulcer in Schizothorax Prenanti.The histopathological examination showed that skeletal muscle appeared degeneration and necrosis, infiltration with inflammatory cells; muscle fibers cracked and dissolved into vacuolus and disappeared. Renal tubule epithelial cells were swollen and lightly vacudar degeneration. Interstitium became narrow and parts of interstitial cells decreased as the result of the dilating of renal glomerulus; renal glomerulus blood capillary hyperemia and silate; the liver cells edema, serious vacudar degeneration and necrosis; the spleen showed a serious hemorrhage, lumphocutes decreased and had lots of hemosiderin in it. The bacteria was very sensitive to chloramphenicol, cefaclor, gentamicin, erythromycin and chloramphenicol, in which chloramphenicol was most sensitive drug and its diameter of the inhibition zone was 22mm.0.8ml Glutaral(20%) added into 3ml growth-promoting media effectively killed D060501 while only 0.08ml mixture which inclued 20%Glutaral and 20% Benzalkonium Bromide could infesticate the bacteria under the same circumstances, which suggested that Glutaral added Benzalkonium Bromide could kill the bacteria in vitro more effectively.