E. Coli: Why can this bacterium be dangerous?

During its evolution, some strains ofE.coli they have acquired genetic mutations that give them harmful properties, among them E.coli called enterohemorrhagic (EHEC noted). Infections caused by EHEC are more or less severe. In the most severe cases, especially in young children, they can cause bleeding diarrhea and / or kidney damage: it is the hemolytic uremic syndrome (HUS). According to the Ministry of Solidarity and Health, between 100 and 160 children are affected each year by HUS. This life-threatening syndrome after an infection with E.coli shiga toxin producer.

Contaminated food: the main source of infection

Bacteria E.coli Shiga – type toxin producers, so named because of their resemblance to those produced by Shigella dysenteriae, another bacterium that causes a form of dysentery: it multiplies at temperatures between 7 ° C and 50 ° C (the optimum temperature is 37 ° C). Some strains grow into acidic foods, up to a pH of 4.4.

The first strain of EHEC was isolated in 1982, during an outbreak of food poisoning in the United States; this epidemic had been caused by burgers whose burgers were poorly cooked. Since then, EHEC has spawned many other outbreaks. The largest EHEC epidemic observed in France occurred in 2005: it was caused by frozen minced meat contaminated with strain O157: H7; 69 cases had been identified, including 57 children under the age of 13.

Monthly distribution of cases of hemolytic-uremic syndrome in children under 15 in France, from 2011 to 2020. Credits: Santé publique France

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E.coli O157: H7 is one of the most harmful serotypes, but other serotypes have been associated with sporadic cases and outbreaks. He E.coli SUH officials, particularly serotype O157: H7, are present in the gut of many ruminants (cows, calves, goats, sheep, deer, etc.); they are excreted in their feces, which can contaminate the direct environment of these animals (water, manure, soil) and the food that comes from them.

Thus, transmission to humans occurs primarily through the consumption of contaminated foods, such as raw or undercooked minced meat, raw milk, raw vegetables, or contaminated germinated seeds; contamination of food of animal origin occurs especially in the slaughterhouse, or during milking. Fecal contamination of water as well as cross-contamination during food preparation can also cause infections.

Contact from one person to another (within the same family or community) represents another possible mode of transmission; some cases of transmission of the bacterium from one asymptomatic person to another have also been reported.

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Toxins that attack blood vessels

EHEC infection usually occurs 3 to 4 days after ingesting contaminated food: it causes diarrhea (sometimes bleeding), abdominal pain, and sometimes fever and vomiting. In most cases, the cure is spontaneous, averaging about ten days.

As the infection progresses to SUH, intense fatigue, pallor, and decreased urine volume are added, which then become darker. HUS has been under increased surveillance by French Public Health since 1996. The most vulnerable people to this infection are children and the elderly. According to the World Health Organization, for 10% of patients, the infection with E.coli producing shiga toxins can progress to SHU, with a lethality rate of 3 to 5%. These toxins induce vascular damage in the intestine, kidney, and brain, causing problems with clotting and high blood pressure.

SUH is the most common cause of acute kidney failure in young children. It can cause neurological complications (seizures, strokes and coma) in 25% of patients and chronic kidney sequelae in 50% of them.

In general, antibiotics are not recommended to treat an EHEC infection: by destroying the bacteria, they would cause the release of shiga toxins into the body, further aggravating SUH. Treatment is based on compensating for deficiencies caused by toxins, through blood transfusion, dialysis and / or plasma exchange.

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Some recommendations to limit the risk of infection

When it comes to hygiene, make sure you wash your hands thoroughly before preparing meals (and even during preparation if necessary), and thoroughly clean kitchen utensils; it is best to use different utensils for raw meat and other foods to avoid. cross-contamination.

Keep in mind that EHEC bacteria tolerate the cold well (they survive for several days in the fridge or freezer), but they are destroyed by cooking. Therefore, meat, especially minced meat, must be perfectly cooked: cooking can destroy this bacterium if the food is “thoroughly cooked”, which means that the temperature must reach at least 70 ° C everywhere for at least two minutes.

Fruits and vegetables, as well as herbs, should be washed, peeled if possible, and eaten raw.

Finally, it is advisable to prevent children under the age of 5 from consuming raw milk, cheese and other dairy products made with raw milk. The Pasteur Institute also recommends avoiding the contact of very young children with farm animals, in particular livestock, sheep and their environment.

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