Bean sprouts to blame for ‘decade-old’ E. coli

Debora MacKenzie 

The strain of Escherichia coli that has caused lethal food poisoning in northern Germany was almost certainly carried by bean sprouts. The bacteria have not been found in food, but epidemiological investigation of what victims ate point towards one German sprout farm.

Meanwhile, mounting evidence suggests the bacterial strain responsible for the outbreak has been circulating in Germany for the past decade – and in people, not cattle as initially supposed.

It is likely to have got into food via human faeces, says Lothar Beutin, head of the national E. coli lab at the German Federal Institute for Risk Assessment in Berlin.

Both the University of Münster, Germany, and BGI, a sequencing lab in Beijing, China, have sequenced the genome of the outbreak bacteria. The results show that it carries genes from a type of E. coli called entero-aggregative, which usually causes persistent but not fatal diarrhoea, plus one for Shiga toxin, which causes bloody diarrhoea and haemolytic-uraemic syndrome (HUS), a severe complication that can be fatal.

Further analysis of the sequence has shown that it is basically an entero-aggregative strain that has picked up Shiga toxin on a lambda phage, a type of virus that infects bacteria and commonly carries genes between them.

The strains of E. coli that produce Shiga toxin, called STEC, are thought to be carried mainly by cattle, which are immune to the toxin. But, says Beutin, "I don’t think [the German strain] came from animals, because we have never seen an aggregative strain in animals." The source of the current epidemic must be human, he says: "There could be another environmental reservoir, but it is hard to imagine."

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