Toxins of Locus of Enterocyte Effacement-Negative Shiga Toxin-Producing Escherichia coli

Maike Krause,Herbert Schmidt,Holger Barth

doi:10.3390/toxins10060241

Maike Krause, Herbert Schmidt + Show 1 more

Open Access

https://doi.org/10.3390/toxins10060241

Copy DOI

Journal: Toxins	Publication Date: Jun 14, 2018
Citations: 17	License type: CC BY 4.0

Affiliation: University of Hohenheim, University of Ulm

Abstract

Studies on Shiga toxin-producing Escherichia coli (STEC) typically examine and classify the virulence gene profiles based on genomic analyses. Among the screened strains, a subgroup of STEC which lacks the locus of enterocyte effacement (LEE) has frequently been identified. This raises the question about the level of pathogenicity of such strains. This review focuses on the advantages and disadvantages of the standard screening procedures in virulence profiling and summarizes the current knowledge concerning the function and regulation of toxins encoded by LEE-negative STEC. Although LEE-negative STEC usually come across as food isolates, which rarely cause infections in humans, some serotypes have been implicated in human diseases. In particular, the LEE-negative E. coli O104:H4 German outbreak strain from 2011 and the Australian O113:H21 strain isolated from a HUS patient attracted attention. Moreover, the LEE-negative STEC O113:H21 strain TS18/08 that was isolated from minced meat is remarkable in that it not only encodes multiple toxins, but in fact expresses three different toxins simultaneously. Their characterization contributes to understanding the virulence of the LEE-negative STEC.

Highlights

Escherichia coli strains that produce Shiga toxins (Stx) occur widely in the gastrointestinal tract of animals and humans
Key Contribution: This review describes the current knowledge about the function and regulation of toxins of locus of enterocyte effacement (LEE)-negative Shiga toxin producing E. coli
This study showed that each toxin of E. coli O113:H21 strain TS18/08 was transcribed and that changes on mRNA levels of the three different toxins corresponded to the growth phase of a discontinuous culture [114]

Summary

Introduction

Escherichia coli strains that produce Shiga toxins (Stx) occur widely in the gastrointestinal tract of animals and humans. In contrast to saa and sab, iha can be found in LEE-negative and LEE-positive STEC as well as other pathogenic E. coli [38,43] Based on these genetic profiling studies, it is assumed that iha is an adhesion-associated gene which seems to be preserved throughout STEC serotypes. This indicates a probable importance for human infections [38,40,43]. Tia can be found in LEE-negative STEC, where it is encoded within a pathogenic island termed SE-PAI [44] In their in vivo study involving two different LEE-negative STEC, Bondì et al [45] showed that tia is needed to mediate the invasion into Caco-2 (human colon adenocarcinoma cells/Cancer coli-2) and HEp-2 cells. The functionality and regulation of the toxins that are found in LEE-negative STEC are described

Toxins of LEE-Negative STEC

Schematic view ofof the targetsites sitesofofthe the toxins

EHEC-Hly

Findings

Conclusions