Listeria monocytogenes is a foodborne pathogen that causes listeriosis, a rare but severe disease with hospitalisation rates above 90% and fatality rates that can reach 20–30% in vulnerable populations, including the elderly, pregnant women, newborns, and immunocompromised individuals. In the EU, approximately 2,738 cases were reported in 2022 alone, a 15.9% increase over 2021, making it one of the most serious foodborne illnesses in Europe. Unlike most bacteria, Listeria thrives at refrigeration temperatures (2–4 °C), tolerates salt and acid, and can form biofilms on processing surfaces, making it exceptionally difficult to eliminate from food production environments.
Ready-to-eat (RTE) foods consumed without further heat treatment carry the highest risk. These include smoked fish, deli meats, soft cheeses, pre-packaged salads, and cooked products that may be recontaminated after the cooking (lethality) step. The critical danger lies in post-processing contamination: Listeria can colonise equipment surfaces, drains, and slicers, and transfer onto finished products before packaging. This is why environmental hygiene in the post-lethality zone is the single most important control point.
Eradicating Listeria is not simply a matter of using an effective biocide. While using the right disinfectant is a necessary starting point, it is only a prerequisite. Listeria monocytogenes is extremely difficult to eradicate from a plant environment due to multiple factors: biofilm formation that shields bacteria from sanitisers; its psychrotrophic nature allowing growth at refrigeration temperatures; high tolerance to humidity, salt, and acid; and its ubiquity in the natural environment, meaning constant reintroduction is likely. A holistic approach combining hygienic design, validated cleaning protocols, environmental monitoring, and staff training is essential.
Listeria monocytogenes is most often found in wet, moisture-retaining areas and in hard-to-reach, hard-to-clean parts of food plants, especially where hygienic design is poor. Typical harbourage sites include drains, floors, joints and seals, damaged or poorly sloped surfaces, and niches where water pools (standing water, puddles, and other damp traps). These conditions support survival and biofilm formation and can lead to spread onto food-contact surfaces if not tightly controlled.
Listeria spreads mainly through water movement, cross‑contamination, and human and equipment activity. It can be transported via floors, drains, cleaning tools, mobile equipment, wheels, footwear, hands, and contaminated surfaces, especially in wet areas.
High‑pressure cleaning, poor segregation of zones, inadequate cleaning of non‑food‑contact surfaces, and movement of people or equipment between areas can all transfer Listeria from harbourage sites to food‑contact surfaces. Once established, biofilms and persistent moisture greatly increase the risk of repeated spread if not effectively controlled.
Effective Listeria control starts with reducing the chance of it entering the site (raw material controls, traffic hygiene, and supplier and inbound handling), then preventing cross-contamination and managing moisture so it cannot persist. All equipment and infrastructure - especially drains, floors, chillers, evaporators, and cleaning tools - must be hygienically designed and genuinely cleanable, then routinely cleaned, disinfected, and maintained to prevent niches where residues and water can build up.
Trained personnel, clean and disinfected PPE, controlled construction and workflow changes, and a robust environmental monitoring programme are essential to identify risks, verify controls, and prevent Listeria from becoming established in the production environment. Further information can be found in our Listeria Guide.
There is no Listeria‑specific chemical. Control depends on effective cleaning, correct application of standard disinfectants, and preventing biofilm formation. Removing soil, moisture, and biofilms—and reducing damp conditions—is far more critical than switching chemistry.
Innovative approaches such as our pre-cleaning technology Diverclean Sonic and our no‑rinse solution Divosan Protect Conc. can further improve how sanitation is executed. By using less water, often at ambient temperature, and shorter cleaning cycles, they reduce damp conditions and condensation — key routes for Listeria cross‑contamination in wet plants.
Effective control of Listeria in drains requires specific, well‑defined cleaning protocols, not just routine wash‑down. Drains must be properly dismantled (e.g. grates, baskets, foul‑air traps) so all internal surfaces can be accessed and cleaned. Alongside daily cleaning, a regular deep clean (typically weekly) is recommended to prevent biofilm formation.
Deep cleaning should focus on thorough soil removal, using strong alkaline or chlorinated alkaline detergents combined with mechanical action (brushing) to reach all surfaces, especially in poorly designed drains. Once cleaned and reassembled, a strong alkaline or chlorinated alkaline detergent—or, where appropriate, a caustic product—should be applied, followed by a sanitizer. Depending on site requirements, peracetic acid‑based or quaternary ammonium (QAC) sanitizers may also be used.
High‑pressure water should be avoided to prevent splashing and spread of contamination. The final disinfectant is best applied gently (for example, by pouring), and surrounding equipment and surfaces must also be disinfected after reassembly to prevent re‑contamination.
If you want to learn more about drains cleaning and disinfection, register for our webinar Hidden Risks, Real Consequences: Hygienic Drainage in Food and Beverage Production.
Hygienic design refers to the principles applied to the construction and layout of food processing equipment and facilities to facilitate effective cleaning and prevent microbial harborage. Equipment with smooth, accessible surfaces, proper drainage, minimal dead spaces, and easily disassembled components significantly reduces the risk of Listeria persistence. Poor hygienic design, such as cracked gaskets, hidden joints, or hard-to-reach areas, creates "safe zones" where bacteria survive cleaning cycles and eventually recontaminate products. International guidelines (e.g., EHEDG) provide standards that food processors should follow to minimize this risk.
An Environmental Monitoring Programme (EMP) is a systematic approach to sampling and testing the food processing environment for indicator organisms and pathogens, primarily Listeria species. The purpose is to detect contamination before it reaches the product, verify the effectiveness of sanitation programmes, and identify persistent harbourage sites (niches). For RTE food producers, a robust EMP is both a regulatory expectation and a best practice to proactively manage risk. Without it, contamination can build silently on non-food-contact surfaces and eventually migrate into food-contact zones.
In a traditional zone-based approach, sampling frequency is determined solely by proximity to the product: Zone 1 (food contact surfaces) is tested most frequently, Zone 2 (adjacent areas) at moderate frequency, Zone 3 (production room areas like floors and drains) less frequently, and Zone 4 (support areas) least frequently.
A risk-based EMP goes further by evaluating multiple risk factors for each sampling site: moisture and water activity, temperature, traffic patterns, historical findings, cleaning difficulty, and product exposure. The key insight is that a Zone 3 drain near an RTE slicing line may need more attention than a Zone 2 surface in a low-risk area. Transitioning from a purely zone-based to a risk-based approach allows food processors to allocate resources where the actual risk is highest.
When Listeria is detected, act quickly: contain the issue first, then investigate, fix, and verify. Hold affected product and, if needed, stop the impacted area; run a root-cause investigation to identify the niche and how it spread; implement corrective and preventive actions (cleaning method changes, repairs, segregation, training); then resample and trend results to confirm it has been eliminated and is not recurring.
The required response also depends on where Listeria is detected and the associated risk to the product:
Practical comparison
|
Scenario |
Product hold? |
Why |
|
Listeria in finished product |
✅ YES (always) |
Product is unsafe / illegal to release |
|
Listeria in Zone 1 (FCS) |
✅ VERY LIKELY |
Direct contamination risk |
|
Listeria in Zone 2 |
⚠️ Often considered |
Close to product |
|
Listeria in Zone 3 (drains) |
❌ NOT automatic |
Indirect risk → depends on escalation |
From 1 July 2026, Regulation (EU) 2024/2895 tightens Listeria requirements for ready‑to‑eat foods that support growth. Compliance must now be demonstrated across the entire shelf life, not only when the product leaves the factory.1 [fsai.ie]
By default, products must meet the criterion “Listeria monocytogenes not detected in 25 g” throughout shelf life. Alternatively, manufacturers may apply the ≤100 cfu/g at end of shelf life approach—but only if supported by robust scientific evidence, such as shelf‑life studies, challenge testing, and/or predictive modelling under realistic conditions. (Source: https://www.fsai.ie)
Overall, the regulation shifts expectations from single test results to proof of control, requiring strong environmental monitoring, validated shelf‑life evidence, and clear documentation showing the product remains safe through distribution and storage.
In December 2024, the USDA's Food Safety and Inspection Service (FSIS) announced significant new measures following high-profile outbreaks linked to RTE meat and poultry products. Effective January 2025, FSIS added broader Listeria species testing to all samples of ready-to-eat product, environmental and food contact surfaces. Previously, only L. monocytogenes was tested; now, broader species testing provides more information about the effectiveness of a facility's sanitation programme. FSIS is also leveraging its National Advisory Committee on Microbiological Criteria for Foods (NACMCF) to review and guide longer-term policy changes on Listeria.
Diversey, a Solenis Company, provides an integrated approach to Listeria management that goes beyond chemistry alone. Our solutions include validated cleaning and disinfection protocols, environmental monitoring support, specialist open plant cleaning (OPC) solutions such as Diverclean Sonic (which eliminates or drastically reduces the pre-rinse step), and rapid pathogen testing tools like SecureCheck and OPCCheck. We also offer technical consultancy, training, and webinars on best practices in food safety. Our philosophy is that effective Listeria control requires a holistic system: the right chemistry is the starting point, but it must be combined with hygienic design, validated processes, competent personnel, and continuous monitoring.