Molecular identification of E. coli and Salmonella species isolated from fresh water fish by Polymerase Chain Reactions (PCR)

Abstract

Bacteriological examination of 400 fish samples taken from Oreochromis niloticus (O. niloticus), Clarias gariepinus, Cyprinus carpio.l (Common carp) and Mugil cephalus (100 from each) revealed isolation of (317) bacterial isolates, which were identified as 171 E.coli isolates and 146 Salmonella sp isolates with an incidence of (53.94% and 46.06 %) respectively. The incidence of E.coli and Salmonella spp. differ among different species of fish under investigation, the higher percentage of bacterial isolates observed in Clarias garipinas (53.31%), followed by (29.97 %), Cyprinus carpio.l (11.99 %), and the lower incidence was observed in Mugil cephalus (4.73%). Frequency distribution of isolated bacteria from the surface lesions and internal organs of examined fish and the antibacterial susceptibility to different chemotherapeutic agents were discussed. PCR based technique was used in identification of E. coli and Salmonella sp., the results showed that E. coli O26 & O111 were positive strains for stx1, stx2 and eaeA genes, E. coli O55 was positive strain for stx2 and eaeA genes, E. coli O91 & O103 were positive strains for stx1 and stx2 genes, E. coli O119 was positive strain for stx2 gene, E. coli O124 was positive strain for eaeA gene and E. coli O128 was positive strain for stx1 gene. In case of Salmonella sp, S. Typhimurium strain was positive for stn, invA and hilA genes, S. Enteritidis strains was positive for stn, invA and hilA genes, S. Virchow strain was positive for invA gene, S. Typhi strain was positive for invA and hilA genes and S. Infantis strain was positive for invA genes.