Challenge tests

Industrial challenge tests with all relevant food pathogenic bacteria

Precise and accurate risk assessment is mandatory wherever contamination with Clostridium botulinum, Listeria monocytogenes and shigatoxigenic or verotoxigenic E. coli can constitute a severe safety hazard. Testing based on model systems or non-pathogenic surrogates will usually not be satisfactory as documentation for this purpose.

Our biosafety level 3* pilot plant facilities are approved to evaluate food safety risks in relation to all relevant pathogenic bacteria. This enables us to simulate the appropriate contamination scenarios from primary contamination of raw materials to secondary contamination after processing.

In our certified facilities, we can perform pilot-scale industrial challenge tests including most relevant food processing steps – the slicing, grinding or chopping of raw materials, brine injection into meat or fish, heat treatment by cooking, autoclaving or steaming, and smoking and fermentation. We can also pack and store food in modified atmosphere and other conditions.


Challenge studies with Listeria monocytogenes

Food safety regulations in the EU, US and many other regions stipulate the need for challenge tests with Listeria monocytogenes in ready-to-eat (RTE) foods. Challenge tests are required by the USDA to validate the effectiveness of post-lethality treatments of RTE products and for documenting the effectiveness of antimicrobial agents or processes within the aimed shelf-life (USDA Regulation, 9 CFR 430.4(a)).

Within the EU, the European Regulation (EC) No. 2073/2005 lays down the microbiological criteria for certain microorganisms in foods and the implements measures which food business operators (FBOs) must comply with. In relation to Listeria monocytogenes, this regulation covers RTE food products with the overall aim of ensuring that the level of this pathogen is below 100 cfu/g at the time of consumption. To this aim, the regulation sets different criteria depending on whether the food product supports growth of L. monocytogenes. If it is documented that the RTE food does not support the growth of Listeria during the designated shelf-life, a limit of 100 cfu/g applies for products placed on the market during their shelf-life. If the food supports the growth of Listeria monocytogenes or documentation is lacking, L. monocytogenes must be absent in 25 g. Due to the nature of this organism, it is close to impossible to guarantee absence of Listeria, even with the best hygienic conditions and procedures. Thus, it is highly recommended to ensure stabilisation of the product by protective measures and subsequently document by challenge testing that the criterion of 100 cfu/g is complied with.

Supplementing EC 2073, the Technical Guidance Document on challenge tests and durability studies for assessing shelf-life of ready-to-eat foods related to Listeria monocytogenes from the European Union Reference Laboratory for Listeria monocytogenes (EURL Lm) describes exactly how specialised laboratories should conduct the needed challenge tests; furthermore, in some EU countries specifications are set by the regional food authorities. By artificial contamination of the food product with a pool of cold-adapted listeria strains, the challenge test aims at simulating the behaviour of L. monocytogenes during processing and distribution under the foreseen storage and handling conditions.

At ISI Food Protection, we conduct such tests according to the EU and regional requirements, and as well as according the EN ISO 20976-1 on “Requirements and guidelines for conducting challenge tests of food and feed  products -Part 1: Challenge tests to study the growth potential, lag time and maximum growth rate” from 2019. In our biosafety level 3* pilot plant, we perform studies of relevant processing steps where there is a risk of primary contamination (e.g., for cold-smoked salmon or fermented sausages), as well as tests comprising re-contamination at slicing and packaging.

Our laboratory is ISO 17025:2017 -accredited to conduct challenge tests by the Danish Accreditation Fund / European Co-operation for Accreditation (Method 41050: Challenge test of Listeria monocytogenes).

Get in touch if you have any questions about the legal requirements or how such tests should be performed.


Challenge studies with Salmonella and VTEC

We perform challenge studies with food-related Salmonella serotypes and pools of verotoxin-producing Escherichia coli (VTEC) strains.

Tests with these pathogenic species are relevant e.g., if there is a need to document the safety of processes such as the fermentation of salami-type sausages.


Challenge studies with Clostridium botulinum

Due to the latest requirements to reduce or ban nitrite in cured meat and other food products, C. botulinum has gained renewed focus as a food safety hazard. Furthermore, we have experienced that plant-based analogue food products may constitute a severe risk related to potential outgrowth of C. botulinum.

We are authorised to conduct challenge tests at pilot-scale level in diverse food products, including simulation of relevant production processes.


Challenge studies with other food-relevant microorganisms

In addition to the above, ISI Food Protection can conduct challenge tests with other relevant pathogens, including Campylobacter jejuni, Staphylococcus aureus (including MRSA strains), Clostridium perfringens, Bacillus cereus and Yersinia enterocolitica.