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J Food Prot. 2017 Mar;80(3):467-475. doi: 10.4315/0362-028X.JFP-16-062.

Prevalence of Listeria monocytogenes in Retail Lightly Pickled Vegetables and Its Successful Control at Processing Plants.

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Division of Bacteriology, Osaka Prefectural Institute of Public Health, Nakamichi 1-3-69, Higashinari-Ku, Osaka 537-0025, Japan.
Izumisano Public Health Center, Kamikawaraya 583-1, Izumisano, Osaka 598-0001, Japan.
Kishiwada Public Health Center, Nodamachi 3-13-1, Kishiwada, Osaka 596-0076, Japan.
Food Safety Promotion Office, Environment Health Division, Department of Health Care and Welfare, Shiga Prefecture, Gotenham 13-45, Otsu, Shiga 520-0834, Japan.
Department of Microbiology, Osaka City Institute of Public Health and Environmental Sciences, Tojo-cho 8-34, Tennoji-ku, Osaka 543-0026, Japan.
Division of Biomedical Food Research, National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya-ku, Tokyo 158-8501, Japan.


Incidences of food poisoning traced to nonanimal food products have been increasingly reported. One of these was a recent large outbreak of Shiga toxin-producing Escherichia coli (STEC) O157 infection from the consumption of lightly pickled vegetables, indicating the necessity of imposing hygienic controls during manufacturing. However, little is known about the bacterial contamination levels in these minimally processed vegetables. Here we examined the prevalence of STEC, Salmonella spp., and Listeria monocytogenes in 100 lightly pickled vegetable products manufactured at 55 processing factories. Simultaneously, we also performed quantitative measurements of representative indicator bacteria (total viable counts, coliform counts, and β-glucuronidase-producing E. coli counts). STEC and Salmonella spp. were not detected in any of the samples; L. monocytogenes was detected in 12 samples manufactured at five of the factories. Microbiological surveillance at two factories (two surveys at factory A and three surveys at factory B) between June 2014 and January 2015 determined that the areas predominantly contaminated with L. monocytogenes included the refrigerators and packaging rooms. Genotyping provided further evidence that the contaminants found in these areas were linked to those found in the final products. Taken together, we demonstrated the prevalence of L. monocytogenes in lightly pickled vegetables sold at the retail level. Microbiological surveillance at the manufacturing factories further clarified the sources of the contamination in the retail products. These data indicate the necessity of implementing adequate monitoring programs to minimize health risks attributable to the consumption of these minimally processed vegetables.


Lightly pickled vegetable; Listeria monocytogenes; Persistent strain

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