Temperature effects on pathogenicity of selected Edwardsiella tarda strain to Japanese eel, Anguilla japonica

Temperature effect on the pathogenicity of selected Edwardsiella tarda V-1 strain to Japanese eel, Anguilla japonica was investigated. To evaluate the effects of both pathogen incubation temperature and fish cultivation temperature on pathogen pathogenicity a two-factor design was conducted. E. tarda was incubated at 15, 20, 25, 30 and 37±1°C, and the fish (mean weight: 100g) were reared at 15, 20, 25 and 28±1°C respectively. The fish reared at different temperatures were infected with the E. tarda incubated at different temperatures. The results of a 4-day LD50 test showed that temperature significantly affected the pathogenicity of E. tarda (p<0.01) and the interaction between the two factors was also significant (p<0.01). For fish reared at 20°C the pathogenicity of E. tarda was the highest at 30°C of pathogen incubation. When the fish rearing temperature was raised to 25 and 28°C, the pathogenicity of E. tarda incubated at all temperatures increased. Isolation testing demonstrated results similar to those of LD50. The selected isolate was virulent to eel, but pathogenicity varied with temperature.

Gross clinical signs and haematological changes associated with artifical infection of Edwardsiella tarda in Koi Carp

The occurrence of diseases is a significant setback for successful aquafarming. One of the common fish bacterial disease syndromes, Edwardsiellosis is caused by Edwardsiella tarda, a gram-negative, rod shaped bacterium associated with several diseases of marine and fresh water fish. In this study, an attempt was made to observe and analyze the onset of clinical symptoms and certain haematological parameters in Koi Carp, Cyprinus carpio L., following artificial infection with Edwardsiella tarda. The disease progress was observed and the clinical symptoms were monitored over a period of 15 days following infection. Fish were sampled at three day intervals to analyse the haematological parameters: total erythrocyte counts (RBC), total leucocyte counts (WBC), haemoglobin content and differential leucocyte count. Clinical symptoms observed included: erratic swimming behaviour, loss of appetite, haemorrhages, dropsy and exophthalmia. There was a significant decrease in the total RBC and haemoglobin levels by the 3rd and 6th day post infection, and an increase thereafter. WBC counts were higher in all infected groups in comparison to the control group. A significant increase in the number of neutrophils was found in the infected group up to the 9th day and a decrease thereafter. The lymphocyte number was significantly less up to the 12th day while the monocyte counts were significantly higher up to the 12th day post infection. The results showed that the bacterium, E. tarda, is pathogenic to Koi Carp. The hematological changes and clinical signs in infected fish reported in this paper will be helpful in the identification and the control of this infection.

Study of bacterial agents on external lesions of cultured Sturgeons in Sngar zone of Gilan Province

This study was carried out to isolate and determine bacterial agents in outer lesions of sturgeons in Shahid Dr. Beheshti sturgeon propagation and rearing center in Gilan province. Five species of sturgeons were studied from viewpoint of lesions. A number of 167 specimens of Beluga, 76 specimens of Persian sturgeon, 27 specimens of Russian sturgeon, 42 specimens of stellate and finally 23 specimens of ship had bacterial lesions in different outer parts of their bodies. After sampling and purification, bacterial cultures and biochemical tests were done. After the isolation of bacteria from lesions, Edwardsiella tarda was selected by means of PCR. To obtain molecular acceptance, a pair of E. tarda special primer, forward primer ETa2-351 and reverse primer (Edwsp-780r) were reproduced. A number of 12 E. tarda DNA sample were identified by PCR. After molecular diagnosis, Persian sturgeon challenged with E. tarda for determination of pathogenesis. Challenge method was done by means of injection of different dilutes of E. tarda into dorsal muscle. Sampling of hematopoietic organs (kidney, spleen and liver) were carried out and located in Boin's fixator to perform pathology survey. Also, in order to survey of existence and effect of E. tarda, sampling of kidney for bacterial culture was done by molecular and biochemical methods. Results showed that the most lesions in all five species belonged to abdominal surface. Skin and scutes of this part were involved in comparison with other parts. Also, It was removed some samples from lesions to pathological survey. Microscopic observations showed some levels of destruction of epidermis layers, necrosis of dermis cells and destruction of muscular layer of skin. On the other hand, invasion of inflammatory cells and haemorrhagic in dermis were clear. Based on biochemical results, Aeromonas sobria, A cavia . A. hydrophila , Acinetobacter lowffii , A.baumanni , A.cakoaceticus, Pseudomonas putida , P fluorescens , P.aeruginosa , Serratia marcescens , Escherichia coli , Enterobacter aerogenes , Edwardsiella tarda , Proteus mirabilis , kelebsiella oxytoca and Staphylococcus sp. were isolated from outer lesions. Results of PCR confirmed that E. tarda was before and after challenge in 200 bp range. LD50, 96h was determined 1.2 x 10^5 (CFU/ml). Pathological experiments showed lesions in the kidney, including hemorrhages, degeneration of glumeruli and tubular epithelia, degeneration and necrosis of interestitium tissue, accumulation of protein casts in the tubular lumen. It was observed haemorhages, engorged blood vessels, congestion of sinusoids, increased of melanine, melano macrophage centers, degeneration and necrosis of hepatocytes in the liver. In the spleen, it was recorded congestion, degeneration, necrosis changes in the white and red pulpa, blood engorged and detachment of ellipsoid wall.