It sounds odd, if not criminal! Yes, our laboratory takes food products and adds the human foodborne pathogen, Listeria monocytogenes! Relax, we don’t let it leave our lab. Rather, we re-package the contaminated food and hold it for the duration of the product shelf life and study it over that time. We’re trying to see if this cold-loving (i.e., psychrotrophic) bacterial pathogen would actually grow in the product if it were to inadvertently contaminate the product in your processing plant. This is called a “Challenge Study,” and whether or not the pathogen can grow in the ready-to-eat products your company makes has a huge bearing on how you will manage your environmental monitoring program, and how the government views your food safety program.
Big Changes Coming for USDA-FSIS Regulated Ready-to-Eat Meats
As a result of a very high profile recent outbreak of Listeriosis from contaminated deli meats, the USDA-FSIS announced changes to the way they regulate ready-to-eat (RTE) meat processors with regards to controlling Listeria monocytogenes. One of the biggest impacts on industry will be that the agency will now sample both products and environment for not only the pathogen (Listeria monocytogenes), but also the indicator, Listeria spp. In 2014, USDA clarified how it would regulate the pathogen in RTE meats, stating that processors could produce products that fall into one of three “Alternatives.” Alternative 1 products receive a lethal treatment in the final package and do not support growth of Listeria monocytogenes; Alternative 2 products have either a post-lethality treatment or inhibitory properties that prevent growth; and Alternative 3 products have neither and rely solely upon sanitation to prevent contamination of the product. There are more testing requirements for Alternative 3 products. Many believe that Directive 50-24 gives RTE meat processors even more reason to get their products out of the Alternative 3 category – meaning re-formulate with antimicrobial agents that restrict the growth of the pathogen during shelf life.
FDA Also Requires Greater Scrutiny for RTE Products that Support Growth of Listeria monocytogenes
The FDA Guidance for Industry on controlling Listeria monocytogenes in RTE foods takes a similar approach. They advise more product testing and environmental testing for products that support growth of the pathogen, than for products that are proven to no support more than a 1-log increase of the pathogen during shelf life. In the Guidance, they coined the term, “Listeristatic” and gave steps to validate that a Formulation is Effective at restricting Listeria monocytogenes growth:
• Historically established formulation controls (e.g., pH less than or equal to 4.4 or water activity less than or equal to 0.92);
• Reference to scientific or technical information (e.g., published, peer-reviewed scientific studies that demonstrate the effectiveness of an antimicrobial ingredient to prevent the growth of L. monocytogenes in products that you manufacture, such as deli salads);
• Previous validation studies (published or internal to your establishment) (e.g., if you determine that an available validation study for one formulation of a deli salad applies at least in part to a second formulation);
• Mathematical modelling (e.g., using models related to inhibition of growth of L. monocytogenes to provide information useful in designing challenge studies);
• Scientifically valid experimental data (e.g., data from challenge studies that you conduct to determine inhibition of L. monocytogenes growth in a specific food).
These approaches are commonly used alone or in combination. For example, some formulation controls rely on a single parameter (such as pH alone or water activity alone), whereas other formulation controls rely on a combination of parameters (such as an antimicrobial ingredient in combination with pH).
- pH less than or equal to 4.4 or water activity less than or equal to 0.92 You may rely on data and information available in the scientific literature as an adequate demonstration that a listeristatic formulation that uses a pH less than or equal to 4.4, or water activity less than 0.92, is effective.
- Listeristatic formulation that combines one or more antimicrobial substances and/or one or more other intrinsic factors
FDA recommends that you demonstrate, through scientific studies that include information from the scientific literature, modelling, and, where needed, challenge studies, that a listeristatic formulation that combines one or more antimicrobial substances and/or one or more other intrinsic factors will consistently prevent the growth of L. monocytogenes. A listeristatic formulation is generally considered to be effective if growth studies that include samples at various points during product shelf life show an increase of less than 1 log cycle over two or more time intervals in the number of L. monocytogenes during replicate trials with the food of interest. Such studies should be conducted by a microbiologist or other food safety expert (e.g., process authority) knowledgeable in food microbiology and pathogen control. This information should provide the parameters (and the associated minimum or maximum values) that you would monitor to ensure consistent control of L. monocytogenes. FDA recommends that you use values for operating parameters that incorporate a margin of safety; this could prove useful in evaluating process deviations.
Get Started Now!
We’re your experts. Challenge studies take time, so get started now. We need a week or to for preparing our cultures and materials. The government requires at least two separate lots (i.e., batches) of product, preferably 3. Then, we have to run the study for at least 1.25X your current shelf life. We can give you rolling updates as the study progresses. Reach out here to learn more.
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