Isolation And Characterization Of Edwardsiella Ictaluri In South Catfish And Pathology And Immunohistochemistry After Experimental Infection

The southern catfish farms unfinished, broken to be the main clinical features of an outbreak of sexually transmitted diseases, the cumulative mortality of up to about50%in Sichuan.In this study, from the onset of southern catfish(20-25g) liver, kidney and isolated two predominant strains(LW101and LW102), artificially infected by intraperitoneal injection and immersion in two ways to determine the disease pathogens. Morphological characteristics of the two pathogens、 determination of the phenotypic, characteristics of the physiological, biochemical characteristics and drug sensitivity.The characteristic showed that:isolates from both ends of the Dayton round, no spore capsule, a single, sometimes paired gram-negative short bacillus, the optimum growth temperature is20～30℃, the optimum pH7.0, containing do not grow more than2%of the salt medium. Characteristics of both strains were cytochrome oxidase negative, fermentation of glucose, reduction of nitrates to nitrites, lack of indole production. To the detection of antimicrobial susceptibility, both of the strains were highly sensitive amoxicillin, ampicilin, cefalexin, cefazolin, streptomycin, neomycin, amikacin, chloramphenicol, florfenicol, roxithromycin, ciprofloxacin, norfloxacin. Based on the phenotypic characteristics and phylogenetic analysis by16S rDNA, both isolates were identified as E.ictaluri. This was the first report on the E. ictaluri infection in south catfish.E. ictaluri is one of the most important pathogens of fish in the word. We used150south catfish to simulation the nature disease each by injection and immersion challenge. After challenge, we recorded the clinical pathological each group. Fish were euthanized at0、2、4、8、12、16、24、36、48、72、96h......When euthanized,5fish were treated with different. Samples of heart, liver, spleen, trunk kidney, stomach, intestine and gills were aseptically collected in par formaldehyde (4%) for24-48h. Using paraffin section for the diagnosis of histopathology changes and using immunohistochemistry to determine the Pathogen in the tissue. The results showed that:the clinical pathological showed caudal peduncle fading and ulceration, beard fading and disruption and’ hang" in the water in anaphase; E.ictaluri mostly appeared in the kidney, spleen and liver of south catfish. Both injection and immersion group appeared positive signal in kidney at12h after injection. Cause renal interstitial cells necrolysis and disappear, plenty of inflammatory cell infiltration, epithelial cells of Renal Tubular degeneration. In the electron microscope, plenty bacteriarennal appeared in interstitial cells and macrophages; Positive signal in spleen at16h after injection and then, spleen diffusive hemorrhage, inflammatory cell infiltration, inflammatory cell necrosis and decrease in the late. In the electron microscope, plenty bacteriarennal appeared in interstitial cells and macrophages. Positive signal in liver at24h after injection and then hepatic sinusoid, vein vascular and central vein congestion, liver cells degeneration, necrosis, fomented necrotic foci gradually. In the electron microscope, mitochondria swelling in liver cells, bacteria appeared in liver cell and hepatic sinusoid; Otherwise, positive signal in brain at48h after injection and showed Brain Edema and non-supportive encephalitis.