What is Listeria monocytogenes and its consequences?

Name

Gender Listeria
Species monocytogenes (generates white blood cells)

General

L. monocytogenes can cause foodborne illness and is one of the most feared pathogenic bacteria in food microbiology. Unlike other bacteria, Listeria can grow in cold, humid climates such as the refrigerator. However, the temperature does affect the growth rate. At 4°C, Listeria grows more slowly than at 7°C.

Suspicious food

High-risk products are mainly those that have been kept refrigerated for long periods and are eaten without being heated.Smoked fish, soft mould cheeses and cooked sliced meats are most commonly associated with Listeria. Other risk products include other meats, chilled pâté, hot dogs, chilled sandwiches and chilled ready meals such as raw salads. 

Diseases

The bacteria enter the intestinal tract through food and penetrate the intestinal mucosa. This stage is accompanied by flu-like symptoms such as fever, chills and headache, which usually disappear by themselves. Highly potent strains of L. monocytogenes can enter the bloodstream and reach the liver and spleen. From there, other organs, the central nervous system and, in pregnant women, the foetus can be infected.

Incubation period

The incubation period, i.e. the time between infection and the first symptoms of illness, is unknown, but is probably 12 hours or even a few days for the milder forms of listeria. For the more severe forms, the incubation period may be a few days to weeks.

Risk groups

Pregnant women, newborn babies, the elderly and people with weakened immune systems are at greater risk from Listeria infection.  
In people with a severely weakened immune system, Listeria can cause serious illnesses such as blood poisoning, meningitis, inflammation of the lining of the heart, gastrointestinal infections and skin and eye infections. 
In pregnant women, infection can lead to miscarriage or premature birth.The susceptibility to Listeria infection varies from person to person. The worse the condition of the immune system, the greater the risk of an infection having adverse effects. In healthy people, the mortality rate is about 3%, but in people in high risk groups, this figure rises to 30%-50%.

Prevention

Complete prevention is not possible, but products that have been properly stored and heated or cooked are generally safe, as the bacteria are killed at a temperature of 75°C. The main danger is cross-contamination. The main risk is cross-contamination, when cooked materials come into contact with raw products or contaminated materials (such as cutting boards). In addition, certain products should not be eaten by those at risk, for example raw milk cheese, cheese with surface flora and long shelf life meats (such as pate); generally products which are stored for long periods of time.