Listeria: what is it?

The bacterium Listeria monocytogenes causes infection, listeriosis. Rare in France (about 400 cases per year), it generally causes minor problems but can be extremely serious in women. pregnant woman and in frail people.

Characteristics of Listeria

Listeria monocytogenes is a bacterium saprophyte Gram+ (Gram positive). Requiring little oxygen (aero-anaerobic), it is widespread in nature and is organized in clusters or short chains. It is found in soil, plants, waste and in the digestive tract infected animals.

Multiplying optimally between 30 and 37°C, it can adapt to the cold and multiply slowly in low temperatures between 0 and 10°C. This acclimatization gives it the ability to spread in refrigerators and end up in foods such as dairy products unpasteurized, poorly washed vegetables and fruits, cold cuts, raw shellfish. An essential factor in its multiplication is linked to the preservation of contaminated food for a duration “long” (of the order of eight days and more) under insufficient refrigeration or rupture of the cold chain bringing the temperature above +5°C.

This germ is all the more dangerous as it does not cause any apparent changes in the food. It does not affect the taste or smell of contaminated food in such a way that it is impossible to detect it. However, it is destroyed by cooking.

Listeria: strong pathogenicity in people at risk

Once ingested, the bacterium gains the lymph nodes from the intestine then the bloodstream to multiply in the liver and the missed where it is usually controlled by the immune system.

Generally, this germ is not very pathogenic for humans in good health (syndrome flu, gastroenteritis) but there is a risk of severe disorders (meningitis) in the immunocompromised subject (lymphocyte T insufficient). At the pregnant womanthe infection may go undetected but lead to neurological damage to the fetus and death in utero. The infected neonate may develop a sepsis or a meningitis. Pathogenicity therefore depends on the state of health of the infected persons and the dose ingested.

Susceptible to most antibiotics (penicillin, gentamicin), the treatment of severe forms is recommended for a period of two to three weeks. The prevention is essential during pregnancy and is based on strict refrigerator hygiene measures, the avoidance of cheeses in raw milk and charcuterie. Particular attention should be paid to cooking food.