Sources and tracking of Listeria monocytogenes in a cold-smoked processing plant

The compliance of RTE foods with the safety criteria for L. monocytogenes in a cold-smoked salmon processing facility, as laid down in the Commission Regulation 2073/2005, was evaluated. The origin of L. monocytogenes was evaluated in the plant by tracing the bacterium along the production line by using the PFGE. The pathogen was isolated from in the raw materials, but none of the batches of semi-processed product was found positive. On the contrary, the pathogen was isolated from all the tested batches in the final product. The number of fish samples positive for L. monocytogenes clearly increased at the end of the manufacturing stage. The results of the enumeration of L. monocytogenes in the final product (0 days of storage), at 30 days of storage and at the end of the shelf-life, show that, none of the finished products were contaminated by the bacterium. Moreover, samples obtained from the environment revealed that the processing line was contaminated with the bacterium. PFGE with AscI and ApaI yielded respectively two and three restriction patterns. The same pulsotypes were isolated both from the fish and from the environment, suggesting that cross contamination occurred. An important factor in foodborne listeriosis is that the pathogen can grow to significant numbers at refrigeration temperatures when given sufficient time. The presence of L. monocytogenes in RTE foods is now regulated within the EU, which provides that L. monocytogenes should be legally below 100 cfu g−1 during the shelf life of such products (Regulation 2073/2005). The findings from this study indicate that there is need of a good control in the manufacture and retail of pre-packaged cold-smoked salmon as not all the samples examined complied with the legal food safety criteria for L. monocytogenes. Moreover, strict attention must be paid to cleaning and disinfection to control the level of L. monocytogenes and to avoid in-plant colonization by this pathogen.