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Abstract
A total number of 150 (50±2 g B.Wt) Oreochromis niloticus, Carp and Catfish were collected a live from Barseek Fish Farm at Behera and farms at Kafr Sheikh and Alexandria Provinces, only 50 fish displayed the clinical signs of diseases. In addition, a total of 50 Oreochromis niloticus and Common Carpwere caught from the River Nile at Kafr El- Sheikh. only 20 fish showed signs of diseases.
The results achieved are summarized in the following points:The most clinical signs of Oreochromis niloticus naturally affected with edwardsiella were typified by: loss of scales from some areas of the skin, excessive mucus allover the body surfaces with petechial haemorrhages over the dorsal musculature. Large necrotic lesions extending down into the musculature in the posterior of the body. especially at caudal peduncle are with rottended fins were observed n some examined fish. These lesions were characterized by hyperemic borders and erniting foul odour skin showed superficial ulcers, especially at the caudal pedunle with extensive haemorrhagic raised areas on the dorsal musculature The reflexes of fish, especially the escape and defensive reflexes were weak or absent.
Successfully isolation of 7 isolates that grew on TSA and were negative for oxidase activities. The colonies appeared after 24 hrs. incubation at 30 °C and were small colonies. They proved to be Gram-negative, motile rods. The biochemical characterization of the isolates indicated that all isolates were positive for indole, H2S production, catalase, methyl red and nitrate reduction and uniformly negative for oxidase, VP, fermentation of sucrose and mannitol. Further biochemical characterization of 7 the isolates was carried out by using the API-20 E system. All tested isolates were positive for lysine decarboxylase, omithine decraboxylase, H2S production, indole and fermentation oI’glucose. Negative results erc obtained for ornithine decarboxylase, arginine dihydrolase. citrate utilization. urease. tryptophane deamination, sodium pyruvate, gelatin hydrolysis, fermentation of mannitol. inositol, sorbitol, rhamnose, sucrose, melibiose and arabinose fermentation.
There were 11 examined E tarda strains able to export hemolysin across the cell wall, the other 29 strains did not secrete hemolysin into their ECP.
E. tarda was highly sensitive to incospectin, neomycin, oxanilic acid. enrofloxacin, ciprofloxacin, oxytetracycline and ampicillin, slightly sensitive to doxacycline. erythromycin. While it was resistant to spectinomycin and chloramphenicol.
This study indicated that the PCR can be used successfully as an ideal method for identification and characterization of the edwardsiel!a from infected fish under Egyptian conditions.