Replication Region Analysis Reveals Non-lambdoid Shiga Toxin Converting Bacteriophages.

Grzegorz Wêgrzyn,Ann-Katrin Llarena,Marina Aspholm,Toril Lindbäck,Kristin O’Sullivan

doi:10.3389/fmicb.2021.640945

Grzegorz Wêgrzyn, Ann-Katrin Llarena + Show 3 more

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https://doi.org/10.3389/fmicb.2021.640945

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Abstract

Shiga toxin is the major virulence factor of enterohemorrhagic Escherichia coli (EHEC), and the gene encoding it is carried within the genome of Shiga toxin-converting phages (Stx phages). Numerous Stx phages have been sequenced to gain a better understanding of their contribution to the virulence potential of EHEC. The Stx phages are classified into the lambdoid phage family based on similarities in lifestyle, gene arrangement, and nucleotide sequence to the lambda phages. This study explores the replication regions of non-lambdoid Stx phages that completely lack the O and P genes encoding the proteins involved in initiating replication in the lambdoid phage genome. Instead, they carry sequences encoding replication proteins that have not been described earlier, here referred to as eru genes (after EHEC phage replication unit genes). This study identified three different types of Eru-phages, where the Eru1-type is carried by the highly pathogenic EHEC strains that caused the Norwegian O103:H25 outbreak in 2006 and the O104:H4 strain that caused the large outbreak in Europe in 2011. We show that Eru1-phages exhibit a less stable lysogenic state than the classical lambdoid Stx phages. As production of phage particles is accompanied by production of Stx toxin, the Eru1-phage could be associated with a high-virulence phenotype of the host EHEC strain. This finding emphasizes the importance of classifying Stx phages according to their replication regions in addition to their Stx-type and could be used to develop a novel strategy to identify highly virulent EHEC strains for improved risk assessment and management.

Highlights

Enterohemorrhagic Escherichia coli (EHEC) is responsible for severe foodborne diarrheal diseases in humans
The results indicate that characterization of the replication region of the Stx phage could potentially be used as a novel strategy to identify highly virulent EHEC strains and with that, improve risk assessment and outbreak management strategies
To explore why the Stx phage TL-2011c produced a high number of phages in the absence of chemical induction (Iversen et al, 2015), we examined the nucleotide sequence of its genome in detail and observed that its replication region differed from the replication region of phage lambda and the Stx phage 933W

Summary

Introduction

Enterohemorrhagic Escherichia coli (EHEC) is responsible for severe foodborne diarrheal diseases in humans. The first known large outbreak of food-borne disease due to Shiga toxin-producing E. coli occurred in the United States in 1982 and was linked to consumption of undercooked contaminated ground beef prepared as hamburgers (Riley et al, 1983). The E. coli O157:H7 strain EDL933 that caused this outbreak is currently reference strain for O157:H7 and EHEC (Riley et al, 1983). The major virulence factor of EHEC is the Shiga-toxins (Stx), whose genes are carried by bacteriophages (Los et al, 2011). Stx are divided into two major families, Stx and Stx, of which. The reference strain EDL933 carries an Stx phage designated 933W (O’Brien et al, 1989; Plunkett et al, 1999)

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