What is Listeria

Listeria and listeriosis

What are Listeria?

Listeria are gram-positive rod-shaped bacteria that have low nutrient requirements and can be found almost anywhere in the environment. The bacterium Listeria monocytogenes, which can cause listeriosis in humans, is of particular importance.

Listeria are quite resistant to environmental influences such as salt or acid. The germ can even multiply at refrigerator temperatures. It also survives freezing, but at least does not multiply. A lack of oxygen (e.g. in vacuum-packed boiled sausage slices or smoked fish) is also not a problem, so that the survivors often have growth advantages over other bacteria. But they grow best at temperatures of 30 to 37 ° C.

Where do Listeria occur?

Listeria are common all over the world. They occur everywhere in the environment, e.g. B. in the soil and on plants, in compost and in sewage. They are also widespread in the agricultural sector (animal feed, digestive tract and animal feces). So you can already in the food production, z. B. during milking or slaughter, get into the food. Therefore, raw foods originating from animals are particularly affected. Vegetables can be contaminated with soil or animal manure, which contain the pathogen. Listeria can also be found on fresh vegetables or leaf salads.

However, they can also be found in food processing companies, especially when cleaning and disinfection measures are not carried out properly. This means that heated or otherwise preserved food for direct consumption can be contaminated during processing (recontamination). As a rule, the bacteria can only become dangerous for humans after they have multiplied (over 100 germs per gram or milliliter).

How dangerous are Listeria?

In healthy people, the infection is usually mild or even undetected without symptoms. For people with a weakened immune system, listeriosis can also be life-threatening. Listeriosis is treated with antibiotics.

The sick and the elderly, newborns and people with a weakened immune system as well as pregnant women are particularly at risk. Since the bacteria can cross the placental barrier after an infection in the mother and the unborn child does not yet have any defense mechanisms, premature or stillbirth or subsequent damage to the newborn can result. Depending on the state of health, the infection can lead to meningitis and encephalitis or blood poisoning in risk groups.

Around 700 Listeria infections are detected in Germany every year. The trend is still increasing, because for years, diseases, especially caused by Listeria monocytogenes, have been increasing continuously in Germany and the EU. The number of unreported cases is significantly higher because many people do not see a doctor.

Symptoms of Listeria Disease

The time between infection and the onset of listeriosis (incubation period) is usually between 3 and 70 days (usually around three weeks). Otherwise healthy people may have a slight febrile reaction that often does not indicate a food cause - possibly with vomiting and diarrhea, similar to gastrointestinal flu, as well as fever, pain in the limbs and muscles, fatigue and a feeling of illness.

With a slight progression, these complaints usually subside on their own within a few days. However, it can also be that the disease remains undetected because there are no symptoms at all.

How can I protect myself?

  • As a precautionary measure, risk groups such as pregnant women and the elderly should avoid products such as raw milk, raw milk cheese (soft cheese), raw sausages, raw meat products such as minced meat or minced meat, raw fish or smoked fish that has been stored for a long time (also in the refrigerator) - except when the food is heated at least 70 ° C core temperature before consumption.
     
  • Caution should also be exercised with these people with ready-to-cook, prepackaged salads, especially if the salad mixes contain sliced ​​white cabbage.
     
  • A strong multiplication of Listeria can also take place during storage in the household (also in the refrigerator). Therefore, proper storage and compliance with hygiene rules in your own kitchen play an important role.
     
  • Complete cooking, frying or baking of food (thorough cooking on all parts of the food at more than 70 ° C for at least two minutes) kills the Listeria.
     
  • Food that is no longer heated before consumption should be prepared as fresh as possible and consumed promptly. If stored temporarily in the refrigerator, these foods should be consumed within two to three days.

This content was created by the consumer centers in North Rhine-Westphalia and Hesse for the network of consumer centers in Germany.