Isolation and characterisation of Shiga toxin-producing Escherichia coli from Norwegian bivalves.

ABSTRACT

Only a few studies concerning Shiga toxin-producing E. coli (STEC) detection in bivalves and their harvesting areas have been reported, and to the best of our knowledge there are no outbreaks associated with STEC from bivalves described. The aim of the present study was to investigate the occurrence of STEC in Norwegian bivalves, and to characterize potential STEC isolated from the samples. A total of 269 samples of bivalves were screened for the presence of stx and eae genes, and markers for the serogroups O26, O103, O111, O145 and O157 by using ISO TS 13136 (2012). The screening returned 19 samples that were positive for stx and eae, and attempts of isolation of STEC were made from these samples. Presumptive STEC were obtained from three samples, and three isolates (one from each sample) were subjected to whole-genome-sequencing (WGS). The WGS revealed that one of the isolates did not carry the stx genes, while the other two were identified as stx2i positive E. coli O9H19 and stx2g positive E. coli O96H19. Neither of the two STEC isolates were positive for virulence markers such as eae and ehx. The results suggest that the occurrence of STEC in Norwegian bivalves is low.