Listeria monocytogenes assay (by count)

Listeria monocytogenes count is an essential microbiological analysis for food safety control. This pathogenic bacterium is the agent responsible for listeriosis, a serious infection that can affect vulnerable populations (pregnant women, the elderly, and immunocompromised individuals).

Capable of growing at low temperatures and in a variety of environments, Listeria monocytogenes poses a major risk to ready-to-eat products, refrigerated foods, and food production chains. Its enumeration allows for the assessment of the actual contamination of a sample and ensures compliance with European regulatory requirements, in particular Regulation (EC) No 2073/2005 on microbiological criteria for foodstuffs.

Objectives and purpose of the census

This analysis aims to:

• Quantify the population of Listeria monocytogenes in a food product, ingredient or surface.
• Check microbiological compliance with regulatory thresholds (generally absence in 25 g or < 100 CFU/g).
• Evaluate the effectiveness of cleaning and disinfection procedures in production workshops.
• Monitor the microbiological quality of products with extended shelf life.
• Identify potential sources of contamination in the manufacturing chain.

Counting is a quantitative method, complementary to the qualitative search for Listeria monocytogenes , which aims only to detect its presence or absence.

Analytical methods

Listeria monocytogenes testing is carried out according to standardized methods, including ISO 11290-2 , which describes the method of enumeration on selective culture media.

Enumeration on specific culture medium
The sample is homogenized, diluted and inoculated on a selective medium that promotes the growth of Listeria spp. After incubation at controlled temperature, the characteristic colonies are counted, and the results are expressed in CFU/g (colony-forming units per gram) or CFU/mL.

PCR (Polymerase Chain Reaction)
For rapid diagnosis, PCR allows the detection and quantification of Listeria monocytogenes in the sample. This approach is useful in microbiological monitoring programs or for cleaning validation.

DNA sequencing (NGS)
In the context of in-depth studies, sequencing makes it possible to identify the strains of Listeria monocytogenes present, to establish links between contaminated batches and to study environmental persistence in production sites.

The analyses are carried out in ISO 17025 accredited laboratories and can be integrated into HACCP plans, quality audits or process validation studies.

Industrial applications

Listeria monocytogenes testing is essential for:

• Ready-to-eat products (salads, cheeses, deli meats, prepared meals, etc.).
• Food cutting and processing workshops.
• Dairy and plant-based products with an extended shelf life.
• Work surfaces and packaging areas.
• Raw materials or ingredients at risk.

This analysis allows quality and food safety managers to control critical points and ensure that safe products are placed on the market.

Affected matrices

• Dairy products and matured cheeses
• Deli meats and processed meats
• Ready-to-eat vegetables
• Long-life refrigerated products
• Environmental samples (water, surfaces, materials)

Recommended Related Analyses

For comprehensive microbiological monitoring, YesWeLab recommends combining the following:
Salmonella spp. testing – another major pathogen in food.
Total coliform and E. coli counts – indicators of hygiene and fecal contamination.
Yeast and mold counts – to assess the microbiological stability of products.
Process water analysis – to control potential sources of microbiological contamination.

Why choose YesWeLab?

YesWeLab relies on a network of partner laboratories specializing in food microbiology and accredited to ISO 17025.
Our analyses adhere to standardized protocols and offer complete traceability of results. We support manufacturers in implementing self-monitoring plans, validating cleaning processes, and tracking production batches.

Thanks to our digital platform, you can easily order, track and view your analysis results, with personalized scientific support.