Urgent scientific and technical assistance to provide recommendations for sampling and testing in the processing plants of frozen vegetables aiming at detecting Listeria monocytogenes

L. monocytogenes, vegetables, fruits, freezing plant, handling facilities, critical sampling site, microbial source tracking
First published in EFSA Supporting Publications
3 Julio 2018
29 Junio 2018
Technical Report


EFSA was requested to provide recommendations to the European Commission on the sampling strategies and established microbiological methods most appropriate for maximising the sensitivity of detection of L. monocytogenes in processing water and the environment of premises producing frozen fruits, vegetables or herbs (FVH) as well as on the final food produced; and on the identification of critical sampling sites (CSSs) for environmental monitoring of L. monocytogenes. Seven steps are defined for a fit‐for‐purpose sampling strategy which is expected to support competent authorities and food business operators in foodborne outbreak investigations where frozen FVH are implicated. The relevant CSSs can be defined based upon critical inspection inside a freezing plant and the background information described in this report. Typical non‐food contact surfaces where L. monocytogenes can harbour in a freezing plant include: floors, especially cracks and crevices, walls, drains, ceilings, overhead structures, catwalks, wash areas, condensate and standing water, wet insulation in walls and around pipes and cooling units, rubber seals around doors, especially in coolers, metal joints, specially welds and bolts and contents of vacuum cleaners. L. monocytogenes is also commonly found on equipment used for food processing, preparation, storage, and transportation such as freezing tunnels, castings bowls, blade spinner, slicers, knives, cutting boards, conveyor belts, gloves joints, gaskets and dead ends. A concerted effort should be made to plan the sampling around production batches and environmental CSSs. Sampling procedures should be performed as exhaustively as possible covering the largest number of CSSs and samples per CSS to gain insight into the potential variability of the contamination sources. EN ISO standard method 11290‐1 is recommended for L. monocytogenes detection. Characterization of L. monocytogenes isolates using well established molecular techniques is needed to identify strains from positive samples and establish links between isolates from humans and from implicated FVH.

biocontam [at] efsa.europa.eu
Question Number
On request from
European Commission