الفهرس 
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Abstract
In this study Edwardsiella tarda is a common fish pathogen, it causes one of the most significant septicemic diseases responsible for mass mortality in freshwater fishes and consequently high economic losses. This study was carried out to investigate prevalence of E. tarda among 0. niloticus (Nile tilapia) and C. gariepinus(African catfish) at Dakahlia Governorate and to characterize the isolates phenotypically and genotypically in addition to detection of virulence genes (edw1,cds1,qseC,pvsA) in them by PCR assay and multi-drug resistance genes(B-lactames genes ,plasmid-mediated quinolone resistant genes,sul1 gene, aadA1gene,tetAgene). Therefore, (100) samples of 0. niloticus and (100) samples ofC. gariepinus collected from different localities at Dakahlia Governorate during the period fromApril 2019 to April 2020. Fish samples were subjected to clinical and post-mortem examination then bacteriological examination from liver, kidney and spleen. The suspected isolates were characterized by cultural and morphological characters, some conventional biochemical tests and API 20E system then by PCR assay. 24 diseased fish were characterized as infected with E. tarda [10 from 0. niloticus (10%) and 14 from C. gariepinus (14%)] with 44 E. tarda isolates with percentage of 22%. The phenotypic characterization of the isolates revealed that they were homogenous. Furthermore, gyrB1 gene (specific common gene) was demonstrated in all E. tarda isolates by PCR. Results of this study indicated that polymerase chain reaction is very reliable and rapid method for identification of E. tarda isolates which may be helpful in prevention and control of Edwardsiellosis.