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 O. niloticus (Nile tilapia) and C. gariepinus (African catfish) at Sohag Governorate and to characterize the isolates phenotypically and genotypically in addition to detection of Major fimbrial subunit gene (etfA) in them by PCR assay.
Therefore, 93 samples of O. niloticus and 87 samples of C. gariepinus collected from different localities at Sohag Governorate during the period from March 2014 to March 2015. Fish samples were subjected to clinical and post-mortem examination then bacteriological examination for 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. 9 isolates were characterized as E. tarda [4 isolates (E1-E4) from O. niloticus (4.3%) and 5 isolates (E5-E9) from C. gariepinus (5.7%)]. The phenotypic characterization of the isolates revealed that they were homogenous except in citrate utilization and similarity percentage between them was ranged from 96.3 to 100%. Furthermore, Major fimbrial subunit gene (etfA) 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.