What is it and how to prevent Listeria



Listeria Monocytogenes is a food pathogen of great interest due to its incidence and its high mortality rate associated with listeriosis (one of the main deaths due to food disease). It is a Gram positive, anaerobic facultative bacillus that can grow or survive in a wide range of pH, temperature, saline concentration and low water activity.

It is a bacterium that is widely distributed in the environment (water and soil) and grows at low temperatures persists in the food industry, is often found in sinkholes, structures or elevated areas or hidden areas that are difficult to clean. Therefore, it can be found in a variety of raw foods, as well as processed and processed foods made from unpasteurized milk.

In addition, it has the capacity to form biofilms which makes it especially resistant since it protects the cells from adverse conditions of desiccation, heat, the presence of antimicrobial substances (disinfectants).

It must also be borne in mind that it has the ability to adapt to disinfectants applied to cleaning and disinfecting industries, which makes it difficult to eliminate them.

The effects of this disease are gastrointestinal symptoms, fever, muscle aches, vomiting, diarrhea, neck stiffness, confusion and weakness, and may cause death in the case of a serious infection and not treated in time.

There are groups of people who are more at risk because the effects caused by this bacterium are more serious, the risk groups are adults over 50 years old, adults with weakened immune systems, developing Fetuses, newborns and pregnant women.

A study conducted by the European Food Safety Authority (EFSA) in 2010-2011 refers to the presence of Listeria monocytogenes in ready-to-eat foods. Said study was carried out in retail establishments for fishing, meat and cheese. We analyzed 3,053 batches of smoked or marinated fish packaging, 3530 meat products and 3452 cheeses. Of these three groups, the smoked or marinated packaged fish was the one that obtained the highest prevalence of this bacterium at the end of its useful life and in turn the group in which more counts greater than 100 cfu / g were made. Taking into account all groups, a total of 0.84% ​​of samples analyzed with the presence of Listeria monocytogenes exceeded 100 cfu / g at the end of the product's useful life.

At present the outbreaks are linked to dairy products, especially soft cheeses, fruits and vegetables.

As for cases in Europe of Listeriosis, a total of 2,536 were registered in 2016, this figure multiplies 1.4 of those detected in 2012.

If we focus on Spain, during the last years the incidence of the disease has multiplied. In 2016 there were 363 cases compared to 109 that were registered in the year 2012.


We, the consumers, could avoid the Listeria by taking the following measures:

1/ Do not drink raw milk
2/ Wash hands, utensils, surfaces and cutting boards after handling raw foods
3/ Separation of cooked foods from those without cooking in our refrigerator
4/ Consume perishable foods with the least possible delay
5/ Wash fruits and vegetables with plenty of water.


While the food industries must take measures in this regard, such as:

1/ Extreme cleaning and disinfection of utensils, machinery and facilities
2/ Avoid cross contamination between foods that have undergone a heat treatment and those that do not
3/ Do not break the cold chain of food as this favors the growth of the bacteria-
4/ Include the risk for listeria contamination in the manufacturing process to carry out an adequate control.
5/ Control the environment, vectors, filters, ventilation and waste
6/ Review of cleaning products


About the Author

Irene Parra

Leave a comment