What is the significance of Listeria monocytogenes in food?
Oct 23, 2019 - Microbiology
What is the significance of Listeria monocytogenes in food?
Profile "Listeria monocytogenes"
General Information and Origin
Listeria monocytogenes is increasingly playing an important role as an infectious agent, as the reported number of cases is continuously rising.
Although listeria are primarily soil dwellers, these bacteria are widely distributed in the environment. Listeria can be found on plants, in wastewater, and in the stool of healthy and sick animals. Due to their wide distribution, listeria are regularly found in raw animal and plant foods (e.g., meat, poultry, milk, vegetables, fish, and seafood). They also play a significant role in processed foods (e.g., meat and sausage products, smoked fish products, mixed salads).
Despite comprehensive hygiene measures in food production facilities, they can establish themselves in certain ecological niches and persist there. They are often found in moist areas in slimy films or biofilms.
Significance
These bacteria can cause very severe illnesses, particularly among pregnant women, infants, the elderly, and sick individuals. The proportion of fatalities is relatively high in these populations.
Such cases can be avoided by adequately cooking food and comprehensive hygiene during production. It should be noted, however, that Listeria monocytogenes can still multiply at refrigerator temperatures. Short storage times and low temperatures < +2 °C are necessary to prevent the growth of these bacteria.
Important Causes of Elevated Germ Counts
- Hygiene errors during production (e.g., contaminated working utensils, surfaces, and equipment, ...) or biofilm formation in hard-to-reach places
- Cross-contamination between raw and processed foods
- Processing of contaminated raw materials
- Insufficient cooling and/or extended storage of foods
- Inadequate heating of foods
Growth Conditions
- Temperature: Growth at 0 - 45 °C
- pH: Growth at 4.5 - 9.0
- aw: Growth up to min. 0.93
- Salt tolerance: max. 10%
- Oxygen requirement: facultatively anaerobic, multiplication in vacuum packaging and packaging with protective atmosphere possible
At what temperatures do these microorganisms die?
In general, it can be assumed that these bacteria are killed when heated to +72 °C for at least two minutes or by an equally effective process. In foods, it must be ensured that this temperature-time combination is reached in the core of the product to safely kill the bacteria.
Further Information and Literature
- www.rki.de: under "Infectious Diseases A-Z"
- www.bfr.bund.de: under "Food Safety"
- www.lgl.bayern.de: under "Food" and then "Hygiene"
- Food Microbiology, J. Krämer and A. Prange, 7th edition 2017
- Microorganisms in Foods, H. Keweloh, 2nd edition 2008
- Handbook of Food Hygiene, K. Fehlhaber/J. Kleer/F. Kley (Behrs Verlag), 1st edition 2007
In our laboratory, we regularly conduct tests for Listeria monocytogenes. We provide fast and reliable results.
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