Listeria and Listerioris in the food industry under scrutiny

One of the most serious food-borne diseases in the EU due to its high morbidity and mortality is Listeriosis. According to EFSA, Listeriosis is the fifth most reported human zoonosis in the EU. In 2021 it rebounded by 14% compared to the previous year, reaching the highest reporting rate since records have been kept. During 2021, 2,183 human cases were reported, of which 923 required hospitalisation, resulting in 196 deaths. However, the overall trend of listeriosis did not show any considerable variation across countries except in Romania with a significant decrease. It should be noted that according to EFSA most of the infections are related to the consumption of convenience foods.

In terms of food-, feed- and animal-borne outbreaks, 23 outbreaks were recorded in 2021, the highest number ever, which could be related to the increased use of whole genome sequencing techniques, which allow the scientific community to better detect and define outbreaks, according to the EFSA report. These outbreaks resulted in 104 cases of which 48 required hospitalisation and 12 died.

In the EFSA report we found 244,357 samples from different categories of convenience food, ready-to-eat, from the distribution or manufacturing stages. Most of the infections and outbreaks are related to the consumption of ready-to-eat foods, meat and meat products, smoked fish and frozen vegetables of domestic origin that do not require any additional heat treatment.

Listeria in the food industry

The possible routes of L. monocytogenes contamination of a food industry are numerous and can occur via dirt stored in the shoe soles worn by plant operators, their clothing, the wheels of transport vehicles used, from animals excreting the bacteria or having it attached to their skin via vegetables brought in from the field, from raw food of animal origin and even from healthy carriers. This is largely due to the fact that in areas with food waste and high humidity the growth of this pathogen is favoured.

In factories, it is very frequently isolated in floor drains, in condensed and stagnant water that can be found after cleaning and disinfection processes, in food remains and in the equipment where they have been processed, in the upper parts of handling rooms, in aerosols produced by sanitisation processes, etc. Other surfaces or product contact areas that may be contaminated in meat and poultry processing plants, including areas after heat treatment, include slicers, saws, decks, shelves and racks, baskets, crates and containers, hand tools, gloves and aprons, packaging materials, packaging equipment, tables, conveyor belts, cleaning brushes, etc. In addition to contamination through food contact surfaces, there are many other possibilities for contamination in the environment. L. monocytogenes can be found and proliferate in many non-food processing areas and, under certain conditions, contaminate product contact areas.

Persistent Listeria

Listeria is a bacterium capable of withstanding even harsh environmental conditions and becoming persistent. When bacteria adhere to and colonise surfaces, they form biofilms showing increased resistance to disinfectants, requiring specific cleaning protocols for their elimination. The application of insufficient hygiene protocols or inadequate hygiene control mechanisms may lead to the occurrence of such persistent L. monocytogenes contamination in facilities, particularly favoured by the formation of biofilms on food contact surfaces. In these L. monocytogenes biofilms the cells are much more resistant to stress and disinfection treatments than planktonic cells. However, depending on the type of substrate on which the biofilm is formed, the resistance of the cells to disinfecting agents will be different, with biofilms formed on a Teflon substrate being more resistant than those formed on stainless steel.

This type of contamination is of particular concern as it reveals inadequate hygiene control and the need to modify cleaning, disinfection and control protocols to ensure the quality and safety of processed foods.

In general, disinfectants used in food industries, such as chlorine releasing compounds, peracetic acid, quaternary ammonium compounds, polymeric biguanide, etc., are effective against Listeria under normal conditions of use. However, it is true that some resistance of L. monocytogenes or other pathogens to develop resistance to biocides has been detected.
We must not lower our guard against this pathogen, so we must be constant in the application of hygiene protocols, using tools for rapid detection of biofilms and contamination, as early detection is essential. The EFSA report stresses that awareness of Listeria and its risks associated with certain consumption habits and types of food such as ready-to-eat products and frozen vegetables must be maintained.

The most effective tool to combat it is through in-depth knowledge: knowing its ecology, its viability conditions, the conditions under which it can form biofilms or its response to disinfectants. These are some of the topics included in the book “Listeria monocytogenes in the meat industry” by Christeyns, an extensive manual aimed at food safety professionals and experts in industrial hygiene which details, among others, the control of Listeria spp. in the industry, practical cases or self-control systems in the meat industry. If you are interested in getting a free copy, you can request it at



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Team CHRISTEYNS Food Hygiene

Company specialized in food safety with headquarters Belgium. With more than 25 years of experience, we offer innovative and effective solutions to the specific hygiene problems of food factories, as well as livestock farms, through a wide range of products, equipment and services designed for the proper cleaning and disinfection of facilities.

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