Listeriosis
Listeriosis caused by Listeria monocytogenes is a serious etiological threat. Over the last decades, a significant increase in infections has been observed, mainly caused by the consumption of contaminated food. Additionally, disturbing information is the fact that approximately 30 percent of infections end in death. Sticks are extremely dangerous for pregnant women, the elderly and those with weakened immune systems.
Characteristics of Listeria monocytogenes
Listeria monocytognes is a relatively anaerobic, motile, Gram-positive bacillus. It is an intracellular parasite. It does not form capsules or spores. It develops at a pH of 4.4 and 4.9 and a temperature of -0.4 to 50°C in aerobic or relatively anaerobic conditions. It is common in the environment. It most often inhabits soil, water, sewage and the digestive tract of many species of animals and people. It is often isolated from farm animals, hence the risk of contamination of products made from raw materials obtained from them with bacilli. It is estimated that over 90 percent of infections are caused by eating infected food.
Bacteria of the Listeria genus are very resistant to unfavorable environmental conditions such as high temperature, salinity and low pH. This is why they are so common in the environment and pose a threat in the food industry. They are able to survive short-term pasteurization and freezing. The bacterium multiplies at temperatures from 2 to 4°C, so food stored at this temperature may be at risk of infection. An additional problem in terms of food safety is the fact that the sticks are able to acquire resistance to unfavorable environmental conditions.
The products most at risk of colonization by Listeria are the least processed ones, e.g. vegetables – especially leafy ones, such as lettuce or spinach, milk and dairy products, meat, cold cuts and fish. A particularly important and increasingly common problem is the presence of pathogenic bacilli in soft cheeses and ready-to-eat delicatessen products. An important aspect of maintaining food safety is maintaining appropriate hygiene during the production process, appropriate storage of products and their transport.
Listeriosis
Symptoms of poisoning appear several to several hours after consuming the infected product. Listeriosis can have various symptoms. Most often, in the first phase of the disease, symptoms include headache, fever, cough, digestive system problems and joint pain. In the advanced phase of the disease, inflammation of the meninges, brain, lungs, endocardium, joints, bones and peritoneum may occur. The most severe cases result in sepsis, acute respiratory failure and even death.
People most at risk of developing listeriosis and its severe course are seniors, children, people struggling with cancer and weakened immunity. It is particularly dangerous for pregnant women and the fetus. It can lead to miscarriages, premature births and even death of the baby. A child who is infected with listeriosis during birth or in the mother’s womb is exposed to serious ailments of the nervous system and other organs such as the liver or lungs. Listeriosis in newborns is characterized by a very high mortality rate.
Detection of Listeria monocytogenes in food
Food testing for Listeri monocytogenes is regulated by the PN EN ISO 11290 standard. According to it, a food sample is multiplied in a selective multiplication broth and then transferred to selective media. The developed, characteristic colonies are subjected to confirmatory tests. For this purpose, identification tests using biochemical reactions, e.g. using carbohydrates, can be used. The analyzed colonies are placed in the dilution liquid. After incubation, the result is analyzed based on the color change. The test also checks the ability of bacteria to hemolyze and hydrolyze esculin. Immunological tests are also commonly used to identify Listeri monocytogenes. Thanks to modern microbiological testing methods, a negative result can be obtained after 48 hours. The development of science allows for the quick and precise detection of pathogens that threaten human life and health.
Enterprises producing ready-to-eat food are obliged to constantly monitor the microbiological purity for Listeria, both in manufactured products and production areas, as well as in the equipment used.
Microbiological criteria of food
In accordance with Commission Regulation I (EC) No. 2073/2005 of 15 November 2005 on microbiological criteria for foodstuffs, Listeria monocytogenes must absolutely not be present in 25 grams of food intended for infants or food for special medical purposes. However, in ready-to-eat food in which its growth is not possible and which is not intended for infants or is not food for medical purposes, Listeria monocytogenes may be present in an amount not exceeding 100 cfu per gram if the product was placed on the market during its shelf life.
