In the case of the O104:H4 strain, there is another cause of intestinal inflammation at the start. The bacteria are still verotoxinogenic, but their interaction with the cells of the intestine is different: they attach themselves to it in a way that is known as aggregative . Thanks to this property, they aggregate on the surface of the cells of the intestine and form what visually resembles a pile of bricks, before releasing their toxins. Moreover, the adhesins present on their surfaces allow them to attach themselves to the cells of human intestines but not those of animals. These strains are therefore restricted to humans and there is no need to look for an animal source of the infection. In this case the strain will be known as Agg-VTEC bacteria (Aggregative Verotoxigenic E. coli).

The origin of these two strains and the mode of infection are not the only differences. The AE-VTEC O157:H7 strain is the third most common bacterial cause of diarrhea in the developed countries while the Agg-VTEC O104:H4 strain is extremely rare. The first affects mainly children of both sexes, although the second attacks adults more frequently, predominantly females (scientists have not been able to explain this difference in risk of infection. One hypothesis is that there is a difference in diet. Females tend to eat more raw vegetables than men. To date no proof has been found for this theory). The incubation period is not the same either, and where the ‘hamburger’ bacteria leads to the HUS syndrome in 7% to 10% of cases, the German strain led to this syndrome in 20% of cases. It is therefore the most virulent from this point of view.

The differences in terms of properties is sufficient to illustrate the importance of clearly naming the strains in order to better diagnose the causes of infection and to identify the origin thereof more easily. Although the scientific community has relied on the previous nomenclature, it still has not found a better way of naming the strains. It is in no way certain that that they will accept the proposition contained in this publication despite the fact that it is more precise and has a certain appeal. “We are going to present this nomenclature in May 2012, at an international congress in Amsterdam which has been organized on the subject of the strains of E. coli that produce Verotoxins. We will arm ourselves with shields and see how the scientific community reacts”, jokes Professor Mainil.