Abstract
Escherichia coli O104:H4 was associated with a severe foodborne disease outbreak originating in Germany in May 2011. More than 4000 illnesses and 50 deaths were reported. The outbreak strain was a typical enteroaggregative E. coli (EAEC) that acquired an antibiotic resistance plasmid and a Shiga-toxin 2 (Stx2)-encoding bacteriophage. Based on whole-genome phylogenies, the O104:H4 strain was most closely related to other EAEC strains; however, Stx2-bacteriophage are mobile, and do not necessarily share an evolutionary history with their bacterial host. In this study, we analyzed Stx2-bacteriophage from the E. coli O104:H4 outbreak isolates and compared them to all available Stx2-bacteriophage sequences. We also compared Stx2 production by an E. coli O104:H4 outbreak-associated isolate (ON-2011) to that of E. coli O157:H7 strains EDL933 and Sakai. Among the E. coli Stx2-phage sequences studied, that from O111:H- strain JB1-95 was most closely related phylogenetically to the Stx2-phage from the O104:H4 outbreak isolates. The phylogeny of most other Stx2-phage was largely concordant with their bacterial host genomes. Finally, O104:H4 strain ON-2011 produced less Stx2 than E. coli O157:H7 strains EDL933 and Sakai in culture; however, when mitomycin C was added, ON-2011 produced significantly more toxin than the E. coli O157:H7 strains. The Stx2-phage from the E. coli O104:H4 outbreak strain and the Stx2-phage from O111:H- strain JB1-95 likely share a common ancestor. Incongruence between the phylogenies of the Stx2-phage and their host genomes suggest the recent Stx2-phage acquisition by E. coli O104:H4. The increase in Stx2-production by ON-2011 following mitomycin C treatment may or may not be related to the high rates of hemolytic uremic syndrome associated with the German outbreak strain. Further studies are required to determine whether the elevated Stx2-production levels are due to bacteriophage or E. coli O104:H4 host related factors.
Highlights
A novel Escherichia coli O104:H4 strain was associated with a widespread and severe foodborne disease outbreak in Germany between early May and July, 2011 [1]
The E. coli O104:H4 outbreak isolate Shigatoxin 2 (Stx2)-phage are most closely situated on the tree to the Stx2phage from E. coli O111:H- strain JB1-95, and more distantly to Stx2-phage from other O111, O103 and O91 serotypes
The relative importance of Stx2-phage heterogeneity and specific Stx2-phage features compared to those of the bacterial host in the virulence of the E. coli O104:H4 outbreak strain awaits further study. It is clear from the German E. coli O104:H4 outbreak that future novel combinations of bacteriophage and bacterial host are likely and that their impact on human health could be devastating
Summary
A novel Escherichia coli O104:H4 strain was associated with a widespread and severe foodborne disease outbreak in Germany between early May and July, 2011 [1]. The E. coli O104:H4 outbreak strain exhibited characteristics typical of other enteroaggregative E. coli (EAEC), including the presence of a paa-containing virulence plasmid, production of enteroaggregative adherence fimbriae (AAF) I, and formation of the stacked-brick adherence pattern on intestinal epithelial cells [3]. The 2011 outbreak isolates were shown to be clonal and part of multi-locus sequence type ST678, which is unique to E. coli O104:H4 strains, and part of the E. coli phylogenetic group B1, which contains a variety of other pathogenic serotypes [5]. Stx production has only rarely been reported among EAEC strains. Only seven sporadic cases of infections with E. coli O104:H4 strains that produced Stx had been reported worldwide in the preceding ten years [7]
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