Listeria monocytogenes

What Is Listeria monocytogenes?

Listeria monocytogenes is a food pathogen that can grow even at refrigerator temperatures. ISO 11290 defines two separate methods: The 1st part is the search for the presence of bacteria (presence/absence in a certain sample amount), the 2nd part is its counting.

Purpose of Listeria monocytogenes

The aim is to determine whether this pathogen is present, especially in cold products that are ready for consumption and have a long shelf life. Listeriosis is rare, but its course is severe in pregnant women, the elderly, and immunocompromised people; That is why the legislation gives a special place to this pathogen.

Which Products Is Listeria monocytogenes Applied To?

Ready-to-eat meat and fish products (smoked salmon, delicatessen)
Soft cheeses and products made from raw milk
Prepared salads and sandwiches
Frozen vegetables and ready meals
Production line surface swabs

In Which Sectors Is Listeria monocytogenes Used?

FoodDrinkAgricultureRetailYem

Standards Related to Listeria monocytogenes

ISO 11290-1 (search)
ISO 11290-2 (count)
ISO 20776 / ISO 16140-2 (alternative method verification)
EU 2073/2005 Annex I (criteria for ready-to-eat foods)

Listeria monocytogenes Conditions

Method: Search (present/absent) or count; is selected according to the criteria to which the product is subject
Enrichment: Two-step enrichment in semi-selective and selective broth
selective media: ALOA (Agar Listeria Ottaviani-Agosti) and a second selective medium
Verification: Biochemical and hemolysis confirmation in typical colonies

Equipment for Listeria monocytogenes

Class II biosafety cabinet
Temperature-controlled incubators
Stomacher (peristaltic homogenizer) and sterile bags
Autoclave and dry air sterilizer
Colony counting apparatus and microscope

Sample Requirements for Listeria monocytogenes

The sample must be sent in its original, unopened packaging.
Products that require a cold chain must be delivered with a cooler and without breaking the chain.
Aseptic sampling rules must be followed; The container must be sterile.
Batch, production date and expiration date information must be reported with the sample.
The amount required for analysis varies depending on the product type; Confirmation must be received before shipping.

Duration of Listeria monocytogenes

Due to the two-step enrichment and verification, search analysis is a process of approximately one week. Rapid methods (PCR-based screening) give negative results early; positive screens are confirmed by culture.

Listeria monocytogenes Procedure

1The sample is weighed and transferred to semi-selective enrichment medium.
2The first enrichment is done at a defined temperature and time.
3Transfer is made from the culture to the second selective enrichment medium.
4Planting is done on selective solid media.
5Typical colonies are selected and confirmation experiments are performed.
6The result is reported as presence/absence or cfu/g in the sample amount.

Listeria monocytogenes Acceptance Criteria

The legislation, not the method, determines whether the result will be considered appropriate or not. The relevant communiqué of the Turkish Food Codex, EU 2073/2005 and 1881/2006 and the specification of the buyer company define different limits depending on the product group; The report gives the measured value and takes the limit from the applicable legislation.

Evaluation of Results

The evaluation depends on which category the product falls into in EU 2073/2005 and the Turkish Food Codex. Products that support reproduction and those that do not are subject to different criteria during their shelf life; Whether it supports reproduction or not is shown by the shelf life study.

Listeria monocytogenes Report

Sample description, batch/lot information and arrival conditions
Sampling method (if taken by the laboratory)
Applied analysis method and reference standard
Analysis date and incubation conditions, if any
Result and its unit
Measurement uncertainty (if requested)
A statement that the result applies only to the specimen submitted for testing

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Turkish Food Codex Microbiological Criteria Regulation
EU 2073/2005 — microbiological criteria for foodstuffs
Law No. 5996 on Veterinary Services, Plant Health, Food and Feed

Food Testing — What Does This Testing Field Cover?

The section below describes the field that the Listeria monocytogenes test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Food testing shows that a product is safe for consumption and contains what its label states. The family works along three axes: microbiological safety, chemical safety and nutritional composition. All three require different laboratory infrastructure, a different body of methods and a different turnaround time.

The most distinctive feature of the field is TIME PRESSURE. A steel specimen can wait on a shelf; a raw milk or fresh meat sample cannot. The time the sample was taken, the transport temperature and how long it takes to reach the laboratory directly determine the validity of the result. In food microbiology the cold chain record is therefore an inseparable part of the test report.

On the microbiological side there are two different questions and they must not be confused. DETECTION of a pathogen is a qualitative question: is Salmonella present in the sample or not? ENUMERATION of indicator organisms is a quantitative question and an indicator of production hygiene. The absence of a pathogen in a product does not show that hygiene is good; if the total mesophilic aerobic count is high, there is a problem in the process.

On the chemical side, pesticide residues, mycotoxins, heavy metals, additives, veterinary drug residues and process contaminants (acrylamide, furan, PAH) are measured. Multi-residue methods in this area (QuEChERS-based LC-MS/MS and GC-MS/MS) can screen hundreds of active substances in a single analysis; limits are defined separately for each product–substance pair.

On the composition side, protein, fat, moisture, ash, fibre, sugar profile, fatty acid composition, vitamin and mineral content are determined. These values are the basis of the nutrition declaration on the label and the tolerance ranges are defined in legislation — the difference between the declared value and the measured value must stay within that tolerance.

There is NO CE marking on food, and this shapes how the field works. Conformity is demonstrated through operating a HACCP-based food safety system, complying with labelling rules and not exceeding contaminant, residue and microbiological limits. A test result produces evidence not for a certificate but for a functioning system.

Allergen management carries particular weight. The presence of an undeclared allergen in a product is one of the most frequent causes of food recalls. Analysis here runs together with cleaning validation: it is shown that the line has been cleaned adequately after a production run containing an allergen and that the risk of cross-contamination is under control.

Voluntary schemes have become effectively mandatory in this field. Retail chains require their suppliers to hold a certificate under a GFSI-recognised scheme (BRCGS, IFS, FSSC 22000); without it, getting onto the shelf is practically impossible.

Method groups in this field

Pathogen detection
Detection of Salmonella, Listeria monocytogenes, Campylobacter, Cronobacter and Shiga toxin-producing E. coli; culture-based and molecular methods.
Indicator counts
Total mesophilic aerobic count, Enterobacteriaceae, coliforms and E. coli, coagulase-positive staphylococci, yeasts and moulds, lactic acid bacteria, sulphite-reducing Clostridia.
Pesticide and veterinary residues
Multi-residue screening by LC-MS/MS and GC-MS/MS with QuEChERS extraction.
Mycotoxins and contaminants
Aflatoxins, ochratoxin A, deoxynivalenol, patulin; heavy metals (ICP-MS), acrylamide and PAH compounds.
Nutritional composition
Kjeldahl protein, fat and fatty acid profile, moisture, ash, dietary fibre, sugar profile, vitamin and mineral analyses.
Allergens and authenticity
Gluten, milk, egg, nut and soy allergen analyses; molecular methods for species identification and adulteration detection.

Commonly confused in this field

Sampling is half the result. A sample transported at the wrong temperature or delayed gives an invalid result even if it is analysed correctly in the laboratory.
The absence of a pathogen does not show that hygiene is good; indicator counts give separate information and the two are read together.
A result from a sample taken from a lot can be generalised to the whole lot only if the sampling plan was set up statistically.
Limits are defined in separate regulations by product group and are updated regularly; a conformity decision based on an outdated limit table may be wrong.
For exports, the limits of the destination country may differ from EU limits; the same product may be compliant in one market and non-compliant in another.

Which decisions these results support

Verification of the HACCP plan and process monitoring
The basis for the nutrition declaration and allergen information on the label
Health certificates before export and compliance with destination market limits
Supplier and lot-based acceptance control
Shelf-life studies and determining storage conditions
Producing evidence for audits under GFSI-recognised schemes

Related Tests

Frequently Asked Questions About Listeria monocytogenes

Does storing it in the refrigerator eliminate the risk of Listeria?

No. Listeria monocytogenes can continue to reproduce, albeit slowly, in cold environments. Therefore, the risk does not decrease in cold products with a long shelf life, but may increase with time.

Should a call or a count be requested?

This is determined by the criteria to which the product is subject. In some products, it is required that it is not present in a certain sample amount, and in others it is required that it not exceed a certain level throughout its shelf life.