Aims: In order to study the transmission of Listeria monocytogenes in a poultry and a pork meat plant, we analysed the contamination by this pathogen over several months. Methods and Results: Five hundred and two isolates of L. monocytogenes were collected and characterized by genotyping and serotyping. Thirty-seven genotypes were obtained by APaI-restriction analysis-pulsed field gel electrophoresis (REA-PFGE) and 35 by SmaI-REA-PFGE and resulted in 50 combined genotypes. The tracing of the contamination in both plants showed that some clones were able to survive for several months. However, some other clones were found only during processing operations, were not detectable after cleaning and seemed to enter continuously into the plant. Conclusions: Some L. monocytogenes strains may persist for a long period in the plant environment Different genotypes can be associated with poultry as well as pork meat. Significance and Impact of the Study: Listeria monocytogenes contamination can be due to contaminated raw materials, bacterial spread and also ineffective cleaning procedures.