Impact of False Positives, Atypical Strains, and New Listeria Species on Listeria monocytogenes Analysis in Europe: Overview and Perspectives

Abstract

Listeriosis, one of the most severe foodborne diseases, remains a leading cause for hospitalization and patient mortality. Recent unconfirmed alerts to Listeria monocytogenes in France have shown that the combination of rapid alternative detection or enumeration chromogenic-based methods with simplified verification tests was not adequate to unequivocally diagnose listeriosis, as some non-Listeria microorganisms may adopt a morphology typical of L. monocytogenes. Added to the risk of false negative results due to rare atypical L. monocytogenes strains, finally, the recent expansion of the Listeria genus generated confusion about species relevant for food safety and the scope of analytical methods. The European Union Reference Laboratory (EURL), the French National Reference Laboratory (NRL) for L. monocytogenes and the WHO Collaborating Centre and National Reference Centre for Listeria, decided to conduct an overview of the impact of L. monocytogenes in France and in Europe. In 2025, an enquiry was launched to collect some feedback from the NRLs of the EU Members States and French official control laboratories. The outcome of this survey revealed the need for revision of the scope and some notes of the EN ISO 11290 Standards, as well as the necessity to collect additional information from both official laboratories’ networks and certification agencies overseeing commercial methods. Specifically, it underlined the potential value of introducing new rules in EN ISO 16140-2 standard, such as adding strains’ specific characteristics in the validation studies and including new foods in the categories of food products.