Detection and characterization of Shiga toxin-producing Escherichia coli from carps from integrated aquaculture system

The objective of the study was to screen carps from an integrated fish culture system for Shiga toxin-producing Escherichia coli (STEC). The isolates of E. coli obtained by selective enrichment and plating were screened for the presence of virulence genes associated with STEC namely stx1, stx2, eae, ehlyA and rfbO157. A total of 33 fish samples were analyzed, 9 (27%) of which were positive for stx genes by direct PCR on the enrichment broth lysates. Eight (24%) of the fish samples yielded isolates harbouring at least one STEC-associated virulence gene. stx2, eae with stx and eae not associated with stx were detected in 3 (33%), 2 (22%) and 4 (45%) of the non-O157 E. coli isolates, respectively. In case of Cyprinus carpio, two samples were found positive for both stx and stx2. Only one sample of Puntius javanicus was found positive for stx alone. However, none of the carp samples from the integrated farm harboured E. coli isolates positive for stx1 and/or ehlyA genes. Occurrence of stx2 gene in fish samples from integrated farming system indicated the possibilities of contamination from veterinary and humans which possess more stx2 associated E. coli than stx1.