Molecular tracking of Listeria monocytogenes in an Iberian pig abattoir and processing plant

The environment and products from an Iberian pig abattoir and processing plant were sampled to investigate the prevalence and genetic diversity of Listeria monocytogenes. The organism was not detected in the pig carcasses prior to processing. Fresh and dry-cured pork did show detectable levels, always ranging below 100 CFU per gram. A total of 163 L. monocytogenes isolates collected during one year were characterized by PCR-based serotyping and pulsed-field gel electrophoresis (PFGE) restriction analysis. Three predominant PFGE types or pulsotypes seemed to persist in the plant. The pulsotype S1 (serotype group 1/2a, 53% of the isolates) was mostly recovered from whole pieces of meat and environmental sites, while pulsotypes S2 (1/2a, 17%) and S4 (1/2b, 21%) were more frequently associated with ground pork products. The pulsotype S4 was also found in a grinding machine, suggesting a possible association of this machine with the contamination of the ground meat products.