Prevalence of Listeria monocytogenes in retailed meat in the Tokyo metropolitan area.

This study was conducted to determine the prevalence of Listeria monocytogenes in retailed meats, comprising beef, chicken, and pork, in the Tokyo metropolitan area. A total of 379 samples of retailed meat were collected from 1998 to 2003, most of which were obtained by simultaneously purchasing the three classes of meat from a shop and then making another simultaneous purchase of meat from the same shop a few weeks later. The prevalence of L. monocytogenes was 28.0%, and the serotypes isolated were mainly 1/2a, 1/2b, 1/2c, and 4b. Comparison of the prevalence of each serotype among the classes of meat showed a predominant distribution of serotypes 1/2a, 1/2b, and 4b in chicken, while serotype 1/2c was dominant in pork. A total of nine cases considered to be due to persistence and/or cross-contamination were found. Most of the strains involved in persistence and/or cross-contamination were of serotypes 1/2c or 4b. These results suggest that contamination in retailed meat in Japan is at almost the same level as in other countries and that chicken has the highest potential as a source of contamination and infection. In addition, we suggest that the ecological niche of serotype 1/2c is distinct from those of 1/2a, 1/2b, and 4b, which may explain why human hosts have less opportunity to be exposed to serotype 1/2c and why there is a lower rate of isolation of this serotype from cases of human listeriosis.