Spotlight on the Escherichia coli bacteria

In May 2011, Germany had to cope with an outbreak of the « E. coli EHEC bacteria». Almost a year later, scientists published an analysis highlighting the real causes of this catastrophe which gave rise to many questions and approximations. In the publication, the researchers also suggest a new nomenclature which should make it possible to better distinguish the different strains of the bacteria which are sometimes confused with each other and which are in fact very different from each other.

E-Coli2The extensive media coverage given to the outbreak is still fresh in the memory. In May 2011, Germany was shaken by an epidemic caused by a hitherto unknown strain of the E.coli bacteria. In a matter of a few weeks, the number of cases multiplied to reach the number of 4,000, of which more than 96% in Germany. All cases of infection were linked to a common food source. As the source was the same and the infection did not spread from person to person, this suggested that the bacteria was not contagious or at least was only very slightly contagious. However, the number of cases multiplied in a very short space of time causing fear to spread throughout all western countries. Within a few days, the bacteria was a main topic of discussion, with each person, politician and journalist having his or her own theory. A few weeks later the epidemic disappeared and the bacteria ceased to be mentioned in the media and was forgotten about, although a lot of unanswered questions remained. Yet, although the outbreak was sudden and short-lived, the bacteria is still present all over the world and infects humans and animals daily even though large outbreaks are still relatively rare.

There are several strains of the E. coli bacteria which cause inflammation of the intestines and diarrhea. But some strains of the bacteria produce Verotoxins which can contaminate the blood and cause a series of symptoms with varying degrees of seriousness from diarrhea which can sometimes be bloody, to the destruction of renal function (hemolytic uremic syndrome or HUS), depending on the resistance of the infected person and/or the concentration of toxins. Once the toxins have contaminated the blood to the point of causing renal failure, it becomes very difficult to treat the disease. Also, if the patient does not have the benefit of a kidney transplant, an operation for which there are very long waiting lists, or dialysis, which involves being hooked up to a machine every day to remove waste from the blood, the disease can prove to be fatal. In the case of the 2011 outbreak, among the almost 4000 people who were infected 55 were victims of kidney failure leading to death.  

Animal versus human strains

More than a year after the outbreak, a team of scientists who specialize in human and veterinary medicine published an article (1) summarizing its emergence and recontextualizing it from the point of view of human medicine in the broader sense and also from an epidemiological, veterinary medicine and bacteriology viewpoint. “The primary aim of the article was to set the record straight. There were a lot of rumors, mistakes and misunderstandings concerning the epidemic. Inundated by this flood of incomplete information, the wider public, just like a large part of the scientific community, did not have the key to an understanding of the causes of the catastrophe”, explains Jacques Mainil, Professor of bacteriology at the University of Liège’s Faculty of Veterinary Medicine.

The first mistake in the case of an epidemic is to systematically point the finger of blame at animals. This knee-jerk reflex is caused by the existence of a common strain of the E. coli bacteria, the EHEC O157:H7 strain. This strain can be found in the intestines of cattle and other ruminants that do not become ill due to the presence of the bacteria: the animals are known as “healthy carriers”. At the slaughter stage, the EHEC O157:H7 strain can unfortunately contaminate meat intended for human consumption. If the meat is not well cooked or properly refrigerated it can proliferate and once ingested by humans, will attack the intestines causing diarrhea which can become bloody before causing kidney lesions in some cases. This strain, which is crudely called “the hamburger bacteria”, often causes infection in men and women: it can involve isolated cases or epidemics according to the source of contamination.

(1) Piérard D., De Greve H., Haesebrouck F., Mainil J.G. O157:H7 and O104:H4 Vero/Shiga toxin-producing Escherichia coli: respective role of cattle and humans. Vet. Res., 2012, 43:13.

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