The Evolution of E. coli

Hugh Pennington

The E. coli outbreak in Germany is enormous. In case numbers (so far) it falls short of the 1996 outbreak in Sakai City in Japan, but the number of those in Germany going on to develop haemolytic uraemic syndrome (HUS), the main complication, which affects blood cells and kidney function, is far greater than in any previous outbreak – 520 on 2 June – and the proportion of those infected that have gone on to develop HUS is also much greater. Germany usually sees about 65 HUS cases every year. In Sakai City only 106 out of 2764 microbiologically confirmed cases developed HUS. The number of deaths in Germany already exceeds the 17 in central Scotland in 1996.

The German problem is being caused by E. coli type O104:H4, which hasn’t been recorded as causing an outbreak before. It is clearly a very hot strain. At least some of its virulence comes from Shiga toxin 2 (Stx2), which is released by the bacterium and sticks to the surface of cells in various organs, including the glomeruli and tubules in the kidney. The cells take up the toxin, which turns off their ability to make proteins, and the cells commit suicide.

Where this strain has come from is currently a mystery. A comparison of victims and well people in Hamburg indicated that the former ate tomatoes, cucumbers and lettuce much more than the latter. But direct attempts to identify the contaminated food have failed. An E. coli strain capable of causing gastroenteritis and HUS was found last week on Spanish organic cucumbers, and Hamburg’s health minister, Cornelia Prüfer-Storcks, went public with this information. At the time it was a reasonable guess that this would turn out to be the outbreak strain. But further work showed that it was not. This didn’t give the cucumbers an absolutely clean bill of health, but it wasn’t the smoking gun. Whether the cause of the outbreak will be established is far from certain. It has been in progress since the beginning of May. Finding contaminated food will depend on whether any remains uneaten and is available for analysis. In many food poisoning outbreaks this doesn’t happen.

Up to now it has been reasonable to assume that the E. coli came from the rectums of cattle or sheep, the natural home of Stx2 carrying strains, and that manure containing it got onto food. But the genome sequence of the strain shows that it is related to another diarrhoea-causing E. coli, a strain from Africa (enteroaggregative E.coli, or EAEC), which only occurs in humans. The sequencing was done in three days by BGI (formerly the Beijing Genomics Institute) in China.

That a nasty new E. coli strain has appeared isn’t surprising. E. coli O157 only showed itself in the early 1980s. In evolutionary terms it is brand new. And E. coli evolves in real time, by taking up DNA from its brothers and sisters as they huddle together in the bowels of their hosts. We may never know where O104 has come from, though we will probably find out quite soon where it lives in nature. Sampling cowpats is straightforward, at least. As for why it’s so nasty, molecular biology will help to find out, but it may take a while: we’ve been studying O157 for a quarter of a century without a full answer. And there’s no knowing whether O104 will stay around for years like O157 or fade away like SARS. The only certainty is that evolution will continue to take us by surprise.


  • 4 June 2011 at 4:10pm
    Geoff Roberts says:
    The experts are still trying to identify the source of the outbreak. Seems that it was definitely not the cucumbers from Spain. There's a theory that it may have started in a restaurant in Lübeck as there has been a large number who ate there who have caught it. Another possibility that it originated in Hamburg durung the harbour birthday celebration there, but it's all speculation right now. Seems that 90% of the patients are female but I don't think that you can read anything into that yet.

  • 5 June 2011 at 10:19am
    David Gordon says:
    It is symptomatic of the woeful quality of much comment on science in our newspapers that one, the other day, was lamenting that "science" had not found the answer to the German E.coli outbreak. Answers often do not come quickly - but the feat of sequencing the genome of this nasty pathogen in three days is breathtaking, certainly to scientists of my (and Professor Pennington's) generation.

    • 5 June 2011 at 5:01pm
      Geoff Roberts says: @ David Gordon
      Agree completely with your first sentence. All of the hype goes into 'Horror germ' and little thought into the actual processes of identifying the little beast. Views in Germany on scientific certainties have declined since the disasters in Japan. "Building nuclear power stations on or near an earthquake rift? An accident is very unlikely." Well there was one, but it won't happen here (in Germany)" That's why Chancellor Merkel, who is a Physicist by profession has changed her party policy completely in the past few weeks.

  • 5 June 2011 at 4:53pm
    Geoff Roberts says:
    The number infected is bnow up to 2500, and 25 people have died after being infected. Lübeck is still apossibility as three distinct groups that ate there have exhibited symptoms. The lates possibility seems to be bean sprouts grown near Uelzen, also delivered to Lübeck but not a definite linkage so far. Hospitals in Hamburg an the region are absolutely at their limits, blood supplies are short. I hope that the numbers start to drop off now.

  • 6 June 2011 at 5:35pm
    Geoff Roberts says:
    Well it wasn't the sprouts, so what now? The number of infections per day has dropped off. Criticisms of the crisis management is growing in the media but as one minister said, his job is to protect the consumers.

  • 10 June 2011 at 1:34pm
    echothx says:
    The potential impact of infectious diseases is curiously absent from debates about future healthcare costs, the emphasis being on chronic diseases (also called Non-communicable-diseases) The combined effects of industrial food production, global trade and human travel, plus the ability to manufacture vaccines and other treatments on a massive scale very quickly, and then market them to an anxious public via popularity seeking politics and circulation seeking media is plenty of material for a health economist or 2 to make some predictions. Surely?

  • 10 July 2011 at 10:47pm
    Steve_11 says:
    Talk about being an outcast! It’s like the cucumber and the bean sprout were part of the popular crowd and then some kid at school spread a nasty rumour about them having head lice and suddenly all the kids avoided them. Only, it’s not head lice, it’s a deadly E. coli bacteria, and it’s not kids, it’s government officials spreading this information. At the end of May a rare and toxic strain of E. coli started to make itself known in Germany and to date, 26 people have died from this outbreak. Thousands more have been infected, not only in Germany but in other European countries, the USA, and Canada. This is not a situation to be taken lightly as it involves one of the largest number of deaths from any E. coli outbreak. For more & some tips to prevent E. Coli visit:

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