Detection of Listeria monocytogenes in commercially broken unpasteurized liquid egg in Japan

Unpasteurized liquid whole-egg samples were collected from six and seven commercial establishments across Japan in 1993 and 1994 and in 2005, respectively. The samples were tested for the presence of Listeria spp. and Listeria monocytogenes. Detection rates of the Listeria spp. were greatly different among the egg-breaking facilities, with a range of 8 to 55%. There was no significant difference in the contamination rate between the samples from 1993 and 1994 and from 2005. L. monocytogenes was isolated from 2 of 487 (0.4%) samples in 1993 and 1994, and 2 of 316 (0.6%) samples in 2005. These detection rates are lower than known detection rates of other livestock products (5.1 to 42%). In 2005, the L. monocytogenes-positive samples were quantified by a most-probable-number counting experiment, and the contamination levels were below 7.5 organisms per 25 g of sample. D55 degrees C-values of 0.59 to 4.08/min were determined for L. monocytogenes isolated in this study. This heat tolerance is in a good agreement with past reports, and slightly higher than that of Salmonella. This study suggests that the legal pasteurization condition of liquid egg is sufficient to ensure microbial safety against L. monocytogenes because the contamination rate and its level are considerably low.