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

Abstract

P a g e | 1 P a g e | 2 ABSTRACT Only few studies concerning Shiga toxin-producing E. coli (STEC) detection in coastal environments and bivalves have been reported and there have been no reported outbreaks by STEC from bivalves in the world.The aim of this thesis was to investigate the occurrence of STEC in Norwegian bivalves, and to characterize potential STEC isolates obtained from the samples.To improve our understanding of STEC, the occurrence was investigated in 269 bivalves collected from harvesting areas along the Norwegian coast in 2016/17. Microbial enrichment of the samples followed by DNA extraction with subsequent screening of STEC-associated genes was performed as described in ISO/TS -13136. Real-time PCR assays were conducted for genes encoding Shiga toxin (stx1 and stx2), intimin (eae) and the five major serogroups of concern (O157, O26, O111, O145 and O103). The screening results revealed the presence of the virulence genes (eae and stx) in 19 of the 269 samples. These 19 samples were selected for isolation of STEC. Colonies obtained from enrichment were screened for presence of stx and positive isolates were further characterized to determine their serotype and virulence profile. For two samples, automated immuno-magnetic separation (AIMS) was performed to facilitate isolation of STEC associated serogroups.Presumptive positive colonies from different serogroups were isolated by AIMS and the serogroup O157 was confirmed by real-time PCR but lacked the virulence genes. A total of three samples from 269 analyzed harbored STEC isolates, therefore, there seems to be a low risk of human infection by STEC in Norwegian bivalves.

Whole-Genome Sequencing and Virulome Analysis of Escherichia coli Isolated from New Zealand Environments of Contrasting Observed Land Use

“…4 ). The final stx 2 variant was recovered from an E. coli isolate isolated from periphyton with a toxin type most similar to that of stx 2i , whose toxin product has yet to be characterized but has not been associated with clinical disease and has been recovered only from raw milk ( 19 ) and bivalves ( 37 ). Other STEC-associated virulence factors ( esp P, etp D, ehx A, iha , and ter ZABCDE) were uncommon and were often identified in isolates that were stx or eae positive (Table S3).…”

Virulence and antimicrobial-resistance of shiga toxin-producing E. coli (STEC) Isolated from edible shellfish and its public health significance

“…Moreover, in another study, all the examined shellfish samples from landing centers and retail fish markets were positive for E. coli (100%) (Prakasan et al 2018). In this regard, Martin and his co-authors reported that any edible marine shellfish species found exposed to fecal contamination, could be regarded as a potential source of STEC (Martin et al 2019).…”

“…Although ruminants are the main reservoirs for STEC, other sources including wildlife, marine environment, and aquaculture could be possible spillover hosts for these bacteria (Kamala et al 2022;Kim et al 2020). Although previous studies have documented presence of several pathogens, there have been few reports on STEC spreading densities from coastal and marine environment (Baliere et al 2015;Kamala et al 2022;Martin et al 2019;Prakasan et al 2018). The present study aims to investigate to which level STEC and their virulence factors are present on the surfaces and accumulated in the tissues of shellfish at harvesting areas of Lake Timsah, Ismailia, Egypt.…”

Crosstalk between Human Microvascular Endothelial Cells and Tubular Epithelial Cells Modulates Pro-Inflammatory Responses Induced by Shiga Toxin Type 2 and Subtilase Cytotoxin

“…Stx2 presents several different variants (Stx2a to Stx2g), which have high homology (93–100%), except for Stx2f variant (69% identity) [12]. Furthermore, two additional Stx2 types, Stx2h and Stx2i, were recently described [13,14]. STEC strains encoding Stx2 are more frequently related to the most severe cases of HUS [15] and the subtype Stx2a cause more serious illnesses than strains encoding Stx2c [16].…”