Towards a global method of Listeria challenge testing in food: diversity requires harmonization

Challenge testing is a key method used to validate food safety control measures against Listeria monocytogenes, a pathogen of major public health concern due to its severe health risks. This review provides a comprehensive overview and comparative analysis of existing challenge test protocols for Listeria monocytogenes, aiming to support improvement and harmonization of international practices. We begin by outlining the role of challenge tests in categorizing foods and determining product shelf-life and their recognition within existing regulatory frameworks. The review then explores how challenge testing is implemented across main global regions with national protocols, particularly those in Europe, the United States, Canada, Australia and New Zealand, alongside relevant international guidelines, particularly those from the Codex Alimentarius and Standard EN ISO 20976-1:2019. A comparative analysis of national and international protocols follows, identifying key methodological differences and similarities. The main divergences include variations in strain selection, storage temperature conditions, and decision criteria used to interpret the growth potential of Listeria monocytogenes. Differences also extend beyond methodology, particularly in laboratory performance assessment and alignment with current best practices. Despite these discrepancies, efforts towards harmonization are acknowledged. This review highlights recent updates and alignments across protocols and proposes a harmonization pathway, identifying scientific priorities and opportunities to develop best practices for strengthening risk assessment and management measures aimed at reducing listeriosis cases worldwide.