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Applied and Environmental Microbiology, July 2000, p. 2866-2872, Vol. 66, No. 7
Department of Biomedical Food Research,
National Institute of Infectious Diseases, Shinjuku-ku, Tokyo
162-8640,1 Eiken Chemical Co. Ltd.,
Shimotsuga-gun, Tochigi 329-0114,2
Nissui Pharmaceutical Co. Ltd., Yuki, Ibaraki
307-0036,3 Tokyo Kenbikyoin Foundation,
Higashikurume, Tokyo 203-0032,4
Niigata Prefectural Research Laboratory for Health
and Environments, Sowa 314-1, Niigatashi
950-215,5 Shizuoka Institute of
Environment and Hygiene, Shizuoka 420-8637,6
and Division of Microbiology, National Institute of Health
Sciences, Setagaya-ku, Tokyo 158-8501,7
Japan
Received 20 January 2000/Accepted 19 April 2000
We studied injury of Escherichia coli O157:H7 cells in
11 food items during freeze storage and methods of isolating
freeze-injured E. coli O157:H7 cells from foods. Food
samples inoculated with E. coli O157:H7 were stored for 16 weeks at
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Selective Enrichment with a Resuscitation Step for
Isolation of Freeze-Injured Escherichia coli O157:H7
from Foods
20°C in a freezer. Noninjured and injured cells were
counted by using tryptic soy agar and sorbitol MacConkey agar
supplemented with cefixime and potassium tellurite. Large populations
of E. coli O157:H7 cells were injured in salted cabbage,
grated radish, seaweed, and tomato samples. In an experiment to detect
E. coli O157:H7 in food samples artificially contaminated
with freeze-injured E. coli O157:H7 cells, the organism was
recovered most efficiently after the samples were incubated in modified
E. coli broth without bile salts at 25°C for 2 h and
then selectively enriched at 42°C for 18 h by adding bile salts
and novobiocin. Our enrichment method was further evaluated by
isolating E. coli O157:H7 from frozen foods inoculated with
the organism prior to freezing. Two hours of resuscitation at 25°C in
nonselective broth improved recovery of E. coli
O157:H7 from frozen grated radishes and strawberries, demonstrating
that the resuscitation step is very effective for isolating E. coli O157:H7 from frozen foods contaminated with injured E. coli O157:H7 cells.
*
Corresponding author. Mailing address: Department of
Biomedical Food Research, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan. Phone: 81 3 5285 1111. Fax: 81 3 5285 1176. E-mail: ykudo{at}nih.go.jp.
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