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Published on August 31, 2025
Brad Peters, Founder, Director, CEO of HRBUniversal & The Plate & Pour Collective Equity Partner Program
A groundbreaking study published in npj Science of Food sheds new light on the complex mechanisms by which Listeria monocytogenes biofilms contribute to persistent cross-contamination within ready-to-eat (RTE) food processing environments. The research, with a particular focus on cold-smoked salmon, provides crucial insights that have significant implications for current food safety regulations and microbial control strategies.
Understanding the Biofilm Effect: A Novel Approach to Listeria Transfer
Scientists from the Spanish Higher Council for Scientific Research (CSIC) and the University of Córdoba meticulously designed an experimental setup to simulate real-world contamination scenarios. They cultivated both multispecies and single-species biofilms using bacterial strains isolated directly from food processing surfaces. These biofilms were grown under carefully controlled low-nutrient and low-Listeria load conditions, mirroring the challenging environment often found in industrial settings.
To quantify the transfer rates of Listeria, the research team employed a sophisticated modeling approach. They tracked Listeria transfer across an impressive 25 successive contacts between the cultured biofilms and fresh salmon slices. This rigorous methodology allowed them to observe and analyze distinct contamination profiles that varied significantly depending on the type of biofilm involved. The study’s innovative approach highlights the often-underestimated role of microbial communities in facilitating pathogen persistence and dissemination.
Regulatory Landscape Shifts: Increased Accountability for Food Business Operators
The findings of this study are particularly pertinent in light of recent changes in European legislation regarding microbiological criteria for foods. In 2024, the European Commission amended existing EU regulations, specifically expanding the responsibilities of food business operators concerning Listeria monocytogenes.
Under the revised regulation, food business operators are now unequivocally accountable for ensuring the absence of L. monocytogenes in 25 grams (g) of an RTE food product. This stringent requirement applies unless the producer can definitively demonstrate that the L. monocytogenes load will not exceed 100 colony-forming units per gram (CFU/g) of the product throughout its entire shelf life. This amendment underscores a heightened emphasis on proactive pathogen control and prevention within the food industry.
Case Study: Multispecies Biofilms Drive Listeria Growth Beyond Regulatory Limits
To vividly illustrate the practical implications of these regulatory changes, the researchers conducted a compelling case study. They simulated a realistic scenario where a single smoked salmon slice from an 80g package became contaminated with L. monocytogenes originating from both single- and multispecies biofilms.
The results of this simulation were striking. After 15 days of refrigerated storage, the L. monocytogenes load in samples contaminated from the multispecies biofilm demonstrably surpassed the critical regulatory limit of 100 CFU/g. In stark contrast, samples contaminated from single-species biofilms often remained below this threshold or exhibited significantly slower growth.
This pivotal finding provides concrete evidence that multispecies biofilms create an environment conducive to more robust L. monocytogenes growth and persistence. It strongly suggests that traditional microbial challenge studies, which often rely on single-species inoculations, may underestimate the true risk of Listeria contamination in complex food processing environments. The study unequivocally underscores the critical importance of considering multispecies biofilm contamination when designing microbial challenge studies, as it is crucial for developing and implementing more effective L. monocytogenes control strategies that accurately reflect real-world conditions.
#Listeria #Biofilms #FoodSafety #RTEFoods #FoodContamination #Microbiology #FoodScience #PublicHealth #FoodSafetyRegulation #FoodProcessing
