Longitudinal study onListeria monocytogenesin Sardinian fermented meat products processing plants: contamination routes, pathogenic profile and evaluation of gene expression in persistent and non-persistent isolates

Detection and enumeration ofL. monocytogeneshave been carried out in 385 samples of raw materials, fermented sausages and environments of different processing plants located in Sardinia (Italy). A subset of ninety - seven strains isolated during a period from 2004 to 2011 were characterized by multiplex PCR-based serogrouping, multiplex PCRs for the presence of virulence genes, PFGE, and quantitative assessment of thein vitrobiofilm formation. In addition, Relative and Absolute Quantification of genes expression ofpocR,mdr,eutGandcbiD, probably involved in the persistence of the pathogen in the environment have been evaluated, in persistent and non-persistent isolates by Real-Time PCR. The 22% of the samples were positive for the presence ofL. monocytogenes. The 31.51% and 15% of the samples tested, food and environment, respectively, were positive for Listeria monocytogenes. Isolates were serotyped as 1/2a, 1/2c, 1/2c and 4b, and presented all the considered virulence genes. PFGE revealed a high heterogeneity of pulsotypes within the plants. PFGE results did not showed the presence of persistent strains among the selection included in this study. The 44% of the tested strains were able to attach to abiotic surfaces forming biofilm. Relative and Absolute qRTi-PCR showed that the genes selected were not involved in persistence.