Scientists in Oslo say sequencing of a particular virulent strain of E. coli O103:H25, which caused an outbreak in Norway in 2006, revealed a resemblance to the 2011 German outbreak strain of E. coli O104:H4, and suggests the two strains are related.

Writing in the online journal PLoS ONE, the researchers with the Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, say fermented sausage was implicated in the 2006 outbreak, which sickened 17 people. Ten of those people developed hemolytic uremic syndrome, the acute kidney disease, and one died. The “extraordinarily high” frequency of HUS was 60 percent.

In last year’s outbreak of E. coli O104:H4, which began in Germany and was linked to sprouts grown from contaminated fenugreek seeds, there were at least 50 fatalities among the 4,000 sickened. The incidence of HUS was 22 percent.

The Norwegian researchers said they sequenced the genome of the 2006 outbreak strain of  E. coli O103 to “elucidate its high virulence and examine potential relationship to other virulent EHEC (enterohaemorrhagic) strains.”

What they found was that it “shows considerable resemblance to the German outbreak strain” and “supports a close relationship” between the two.

E. coli O103:H25 is classified as an enterohaemorrhagic E. coli, or EHEC — bacteria that produce the Shiga toxin known for causing hemorrhaging and HUS.

The German O104:H4 outbreak strain is not an EHEC, but an enteroaggregative E. coli (EAEC) .

The term “enteroaggregative” refers to the way the bacteria aggregates into a stacked-brick pattern and clings to intestinal tracts. Enteroaggregative E. coli are known to cause persistent diarrhea –  notably traveler’s diarrhea — but not HUS. 

But, like EHEC, O104 also releases Shiga toxin into the bloodstream, an adaptation that resulted in at least 826 cases of HUS in the German outbreak.

The theory is that enteroaggregative O104 acquired Shiga toxin-producing DNA from more virulent strains of enterohemorrhagic E. coli. 

“Despite the lack of genes characteristic of EAEC in EHEC O103:H25 NOS, and thus differing in both pathotype and serotype, the genomes of the Norwegian and the German outbreak strains are highly similar,” the researchers wrote.

They add: “The finding of closely related Shiga toxin producing phages and genomes in two outbreak strains of different serotypes and pathotypes, but with a high HUS incidence in common, is remarkable and will be investigated further.” 

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Image source: E. coli O104:H4 outbreak strain from the Robert Koch Institute.