MATERIALS AND METHODS A total number of 40 cultured oniloncus were collected randomly from the ponds of a private fish farm in Kafi El Sheikh Govemorate, Egypt. The Body weights of fish were ranged from 150+10 g. The collected fish were examined clinically with paying an attention to the behaviors in the ponds. changes in color and respiratory manifestations with a special care to the extemal lesions il according to the methods described by Noga [5]. The fish samples were kept in tanks partially filled with the same water of the pond then transported to the Lab. In the Lab. c each fish was rinsed with de-ionized water and the surface of the fish was decontaminated by dipping it in ethyl fo alcohol and lightly flamed. The samples were taken according to Bullar [11 swabs from the different organs of of each fish were inoculated on Tryptic Soya broth then. incubated at 28°C for 24 hour ccording to Austin aud Austin [12].
Isolation and Identification of A. hydrophila: A loop fill from each broth tube was streaked onto the following media: MacConkey's agar Rimler and Schotts RS agai) Oxoid) then incubated at 28°C for 24 hours. Purified isolates were used as stocks for further morphological and identifications. biochemical Bacterial films were Characterization: Morphological prepared from each suspected purified isolate and stained with Gram's stain [13] then examined under the bright field microscope with the oil immeision lens.Biochemical Identification Traditional Methods: The separate colonies were subjected to biochemical identification by the following tests: oxidase "Biomerieux". triple sugar iron agar, indol, Voges Proskauer, urea utilization. Simmon's citrate agar and methyle red according to Collee et al. [14]. B-API 20 E Kits: API 20E kit BioMerieux [15] biochemical f profiling test was performed according to manufacturer's instructions. Finally. isolates were stabbed into tubes containing semi-solid nutrient agar medium and then incubated at 37°C for 24 lus. The incubated tubes were examined for detecting motility of inoculated isolates then preserved in the refiigerator at 4 ts Genomic DNA Extraction and PCR Amplification: DNA of .1. in drophia was extracted by using QIA amp mini kit. oligonucleotide primer for the aerolysin Qiagen. specific ry toxin gene was used according to Wang et al. [16] as us illustrated in Table