Pulsed-field gel electrophoresis (PFGE) typing of Listeria strains isolated from a meat processing plant over a 2-year period

As part of a hygiene monitoring program in a meat processing plant a total of 131 Listeria isolates were detected by sampling different processing areas and meat products within a 2-year period. The isolates were differentiated by means of phenotypic characteristics. Furthermore, the genomic ApaI and SmaI fragment patterns of all isolates were examined by pulsed-field gel electrophoresis (PFGE). PFGE using SmaI and ApaI yielded 15 (Listeria monocytogenes), 20 (Listeria innocua) and six (Listeria welshimeri) pulsotypes. Of the environmental Listeria monocytogenes isolates the predominating PFGE-type B was clearly associated with processing area A whereas PFGE-type E predominated in the meat products. Moreover, the study showed the persistence of closely related Listeria strains over a 2-year period in the environment of this meat processing plant.