Molecular characterization of Shiga-toxigenic Escherichia coli isolated from diverse sources from India by multi-locus variable number tandem repeat analysis (MLVA)

Isolation of Shiga toxin-producing Escherichia coli harboring variant Shiga toxin genes from seafood

Background and Aim:

Shiga toxin-producing Escherichia coli (STEC) are important pathogens of global significance. STEC are responsible for numerous food-borne outbreaks worldwide and their presence in food is a potential health hazard. The objective of the present study was to determine the incidence of STEC in fresh seafood in Mumbai, India, and to characterize STEC with respect to their virulence determinants.

Materials and Methods:

A total of 368 E. coli were isolated from 39 fresh seafood samples (18 finfish and 21 shellfish) using culture-based methods. The isolates were screened by polymerase chain reaction (PCR) for the genes commonly associated with STEC. The variant Shiga toxin genes were confirmed by Southern blotting and hybridization followed by DNA sequencing.

Results:

One or more Shiga toxins genes were detected in 61 isolates. Of 39 samples analyzed, 10 (25.64%) samples harbored STEC. Other virulence genes, namely, eaeA (coding for an intimin) and hlyA (hemolysin A) were detected in 43 and 15 seafood isolates, respectively. The variant stx1 genes from 6 isolates were sequenced, five of which were found to be stx1d variants, while one sequence varied considerably from known stx1 sequences. Southern hybridization and DNA sequence analysis suggested putative Shiga toxin variant genes (stx2) in at least 3 other isolates.

Conclusion:

The results of this study showed the occurrence of STEC in seafood harboring one or more Shiga toxin genes. The detection of STEC by PCR may be hampered due to the presence of variant genes such as the stx1d in STEC. This is the first report of stx1d gene in STEC isolated from Indian seafood.