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Detection, Control and Prevention of Listeria

Being aware of the current concern about recent cases of Listeria in Spain, the laboratories of Tentamus Spain want to inform you about the main causes of infection and techniques for detection, control and prevention of this bacterium.

Listeria monocytogenes is a food-borne bacterium that can cause an infectious disease called listeriosis in humans. Listeriosis is considered as a serious disease, as it has high rates of hospitalization and mortality in risk groups (elderly, pregnant women, newborns, etc.).


Transmission of Listeria monocytogenes


Listeriais a bacterium that can be found in soils, plants and water. In turn, animals can be carriers of this bacterium through the consumption of infected plants and/or feed.

In humans, the consumption of contaminated food is the main route of transmission. The most vulnerable foods that have most frequently caused listeriois in the population are: smoked fish, meat, raw vegetables, unpasteurized milk and dairy products, as well as sausages and meat preparations.


Main Causes of Contamination with Listeria monocytogenes


Regulation (EC) No 2073/2005  establishes the analytical controls that companies must carry out to ensure that food is free of the bacterium and it doesn’t pose a risk to the population. According to Aecosan (Spanish Agency for Food Safety and Nutrition), the main causes of contamination of Listeria in food are:

  • Reduction of the number of microorganisms in food so that, for example, the date of preferred consumption can be increased. When there is a high exposure to other non-pathogenic microorganisms in food, they compete for space and nutrients, making it difficult for listeria to develop to a high level. Fermented foods such as yoghurt or mature cheese are therefore often not on the list of contamination-prone foods.
  • Breakage of the cold chain
  • Oxygen-free product packaging system
  • Failure to reach optimum temperatures for the elimination of bacteria in the manufacturing process. This bacterium is sensitive to heat treatments above 65°C, although it has very particular characteristics, which make it different from other bacteria that produce food infections: it is relatively resistant to acid medium (pH range 4.3 to 9.6) and high concentrations of salt (25.5% ClNa), and can also multiply at refrigeration temperatures (between 2°C and 4°C). In very acidic foods (pH < 4,3) and kept refrigerated, 15 days are necessary to reach risk levels.

Therefore, special attention should be paid to ready-to-eat foods, as contamination can occur after food is cooked, but before it is packaged.


Prevention and Control of Listeria monocytogenes


The resistance of this bacterium, along with the high mortality rates in humans, makes safe food handling paramount to ensure public health.

There is no foolproof solution that can completely prevent Listeria contamination in food, but a proper hygiene and disinfection program can contribute greatly to effective bacterial control. Every food industry must have adequate tools and control plans to prevent possible contamination. These tools range from control models such as Hazard Analysis and Critical Control Points in manufacturing (HACCP) and microbiological minimization plans among other tools, to a good analytical control system, both of ready-to-eat products and work surfaces to verify the effectiveness of the disinfection process.

In order to carry out this effective analytical control, the Spanish Tentamus laboratories provide our customers with various analytical tests for the detection of this bacterium. In addition, we have laboratories accredited by ENAC for the analysis of food safety in food.


Contact us, our team of experts will inform and advise you throughout the process.

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