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This work was aimed at determining the occurrence and diversity of Listeria monocytogenes in a traditional meat-processing facility to reveal persistent contamination. A total of 268 samples, including 196 environmental samples and 72 meat samples were collected during a four-year period, and 70 were found to be L. monocytogenes positive. Molecular serotyping of 77 isolates classified these strains into four serogroups, with the majority of 34 strains in serogroup IIa. To reveal the persistent contamination, subtyping by AscI/ApaI-PFGE was applied. Cluster analysis resulted in strain discrimination into 18 profiles. Strains with PFGE/MLST-ST classification as 1/ ST9, 2/ST14 and 9/ST2 were predominant and considered persistent. Based on the results of PFGE, a spatial and temporal map of persistent L. monocytogenes contamination was drawn. Subtyping by PFGE was used as a reliable tool to reveal persistent contamination and, complemented with virulence characteristics, can contribute to the improvement of L. monocytogenes control programs in food processing. Practical applicationListeria monocytogenes is a food-borne pathogen with significant public health and economic impact. This study, focused on prevalence and tracing of L. monocytogenes strains in a traditional meat-processing facility, revealed persistent contamination by the pathogen. Data of PFGE profiling from repeated samplings over a four-year period facilitated to draw a spatial and temporal map of persistent L. monocytogenes strains spreading in a meat-processing facility and, subsequently, will allow optimisation of cleaning and disinfection measures to ensure hygiene. Based on the detection of virulence factors, persistent ECIII and comK prophage-positive strains were observed, indicating a higher risk of contamination by more virulent L. monocytogenes strains. The obtained results clearly indicate, that most attention should be paid to control strategy improvement in the meat processing chain focused preferably on prevention, not only to final products.

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