2006 年 50 巻 4 号 p. 175-184
Listeria monocytogenes is the causative agent of foodborne listeriosis in humans. Japan has an average of 83 cases of listeriosis per year and an estimated incidence of 0.65 cases per million residents, which is lower than the values reported in some European countries and the United States. Nevertheless, the level of contamination in retail food products in Japan is roughly equivalent to that reported in these countries, where large outbreaks have occurred. Japan might therefore face a similar risk of foodborne listeriosis outbreaks. Ready-to-eat seafood (such as cold-smoked fish) has been linked to sporadic cases of listeriosis. In Japan, a wide range of ready-to-eat seafood products are consumed in great quantities. We investigated L. monocytogenes contamination in commercially available ready-to-eat seafood products during 1999 and 2000. L. monocytogenes was isolated from 13% (12 of 95) of the tested products. All the positive samples were cold-smoked fish products. Molecular typing of the isolates suggested that the products were contaminated with persistent strains that were unique to their respective manufacturers. We investigated manufacturing plant A to trace L. monocytogenes isolates to the source of contamination. As the result of this, a combined analysis of the seasonal prevalence of this bacterium and molecular typing of the isolates in the plant suggested that the product contamination was associated with the slicing machines. Implementation of an effective washing and cleaning regime for the slicing machines resulted in a marked decrease in the incidence of L. monocytogenes contamination of the finished products.