Risks of Contamination with Listeria monocytogenes and Salmonella spp in Ready-to-Eat Food


In the modern world, people have become accustomed to outsourcing everyday tasks, including cooking. This trend is evident in the growing consumption of ready-to-eat products (RTE). For instance, in Europe in 2021, the average per capita consumption of such dishes reached 15 kg.

The increasing demand for RTE products, while benefiting the retail and public food sectors, also brings about new microbiological challenges concerning food safety. Pathogen environmental monitoring reveals that RTE dishes, especially those with multiple components, can be susceptible to contamination by various bacteria, including different strains of Listeria spp and Salmonella spp

This issue demands immediate attention, given the data from EFSA, which indicates that Salmonellosis ranks as the second most prevalent zoonotic disease in EU countries, with an annual incidence rate approaching 91,000 cases. Listeriosis, on the other hand, is fifth in terms of the number of registered zoonotic diseases in the EU, with 2,183 cases.

Both Listeria monocytogenes and Salmonella spp possess the ability to adapt to diverse conditions, persist in them, and proliferate. Typically, in indoor environments and at average air temperatures, the lifespan of these bacteria can vary from a few hours to several days. The duration of their survival depends on several factors, including:

  • Temperature and Humidity: Environmental conditions play a vital role. Bacteria's lifespan varies depending on factors like temperature and humidity.

  • Surface Type: Bacteria can survive longer on porous surfaces such as wood or fabric compared to non-porous surfaces.

  • Sunlight Exposure: Direct sunlight, with its UV radiation, can inhibit bacteria. Bacteria exposed to sunlight tend to have shorter lifespans.

  • Presence of competitive Microorganisms: When bacteria face competition from other microorganisms, like in cases of coexistence, the lifespan of Listeria and Salmonella decreases significantly.

  • Environmental Characteristics: The environment's characteristics, such as moisture content, acidity levels, and protein content, impact bacterial survival. Products with high moisture, low acidity, and high protein content are more likely to yield positive results in swab tests in the food industry.

  • Use of Preservatives or Processing: In products where preservatives or pasteurization are used, bacteria tend to survive for shorter periods.

At which stages of production is Listeria monocytogenes Salmonella spp advisable?

Identifying Listeria monocytogenes and Salmonella spp is crucial at various stages of production. It's vital to note that, even under less-than-ideal conditions, the risk of contamination with these pathogens in the production of RTE supermarket products always exists.

Let's explore when and how these pathogens can infiltrate RTE products: 

Quality Control Testing during the supply of raw materials for the production of RTE food. 

Quality control testing is a pivotal step in inspecting incoming raw materials, which encompass water, both raw and processed meat, dairy items, vegetables, and fruits. Detecting contaminated products promptly is essential to prevent potential contamination of others.

By addressing these issues at the raw material stage, we ensure the safety and quality of the final RTE products, safeguarding consumers from harmful pathogens like Listeria monocytogenes and Salmonella spp.

Environmental Monitoring and Assessment during the production of RTE food.

Both of these bacteria have a remarkable ability to endure on various surfaces.

Listeria, in particular, exhibits resilience in production environments and equipment. It possesses the capability to form biofilms, which act like protective shields, allowing it to cling to surfaces and shield itself from external influences.

On the other hand, Salmonella employs adhesive structures to remain attached. Depending on the level of contamination, these bacteria can even develop resistance to antimicrobial agents, demanding more rigorous processing measures.

Improper storage of RTE dishes, especially in warm or humid conditions, creates a breeding ground for bacterial growth. Furthermore, contamination can occur when prepared dishes come into contact with other products containing Listeria monocytogenes or Salmonella spp, facilitating the transfer of these harmful bacteria. Hence, maintaining stringent quality control of RTE products is of paramount importance in ensuring food safety.

Utilizing Environmental Swabbing for Ready-Made Product Safety

When it comes to safeguarding RTE products, environmental swabbing emerges as a powerful tool. Improper storage, especially in warm or humid conditions, can become a breeding ground for accelerated bacterial growth. Moreover, the risk of contamination looms large when prepared dishes come into contact with other products housing Listeria monocytogenes or Salmonella spp.

In this scenario, the critical importance of ensuring top-notch quality control for ready-made products becomes abundantly clear. Environmental swabbing, as part of a comprehensive strategy, helps in early detection and mitigation of potential hazards, reinforcing the safety of these products for consumers.

The risk of Listeria monocytogenes and Salmonella spp. contamination in ready-to-eat products during transportation. 

It's crucial not to underestimate the potential for Listeria monocytogenes and Salmonella spp. contamination in RTE products during transit. What's worth noting is that the threat of these contaminants extends beyond the production phase, making environmental monitoring an ongoing necessity.

This risk continues during transportation, particularly for products lacking hermetic packaging or with damaged packaging. Hence, vigilance throughout the entire supply chain is imperative to ensure the safety and integrity of these products, safeguarding consumers from potential health hazards.

The Importance of Environmental Monitoring During the Sales Process

It's imperative to recognize the risk of Listeria monocytogenes and Salmonella spp. contamination doesn't dissipate during the sales process. Some strains of these bacteria have evolved to thrive at lower temperatures, even within refrigerators. This means that the threat extends to supermarket shelves, where Listeria monocytogenes and Salmonella spp can exhibit moderate activity. This activity, although reduced, is still sufficient not only for their potential survival in products but also for contaminating adjacent items.

Additionally, supermarket shoppers themselves may inadvertently come into contact with these bacteria and transfer them through their hands. Hence, simply treating surfaces with appropriate agents and adhering to hygiene standards by employees might not always suffice.

Just as during transportation, ensuring complete hermetic sealing of product packaging is crucial to prevent potential contamination of food products. Contamination with Listeria monocytogenes and Salmonella spp is a lurking threat at every stage of the production and sale of RTE products. While rigorous quality control of raw materials, meticulous monitoring of storage conditions, and maintaining high production hygiene are undoubtedly essential, risks persist even in subsequent stages.

Environmental monitoring plays a pivotal role in systematic surveillance. It not only aids in the detection of Listeria and Salmonella pathogens but also facilitates testing for hygiene and cleanliness indicators. We recommend incorporating ATP and E. coli tests to maintain control over hygiene and cleanliness levels, which can be conveniently accessed through the provided link. This comprehensive approach ensures that the safety and quality of RTE products are upheld throughout the entire journey from production to the hands of consumers.

Back to Blog