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Applied and Environmental Microbiology, December 2000, p. 5536-5539, Vol. 66, No. 12
Obihiro University of Agriculture and
Veterinary Medicine, Obihiro, Hokkaido
080-8555,1 Hokkaido Institute of
Public Health, Sapporo, Hokkaido 060-0819,2 and
Graduate School of Agriculture and Life Science, The
University of Tokyo, Tokyo 113-8657,3 Japan
Received 31 May 2000/Accepted 30 September 2000
An outbreak caused by salted salmon roe contaminated with
enterohemorrhagic Escherichia coli O157 occurred in Japan
in 1998. Since about 0.75 to 1.5 viable cells were estimated to cause
infection, we presumed that O157 might enter the viable but
nonculturable (VNC) state in salted salmon roe and consequently that
viable cell numbers might be underestimated. Although
patient-originating O157 cells could not grow on agar plates after
72 h of incubation in 13% NaCl, they were resuscitated in yeast
extract broth, and more than 90% of the cells were shown to be viable
by fluorescent staining, suggesting that almost all of them could enter
the VNC state in NaCl water. Roe-originating O157 was resistant to NaCl because it could grow on agar after 72 h of incubation in NaCl water, but about 20% of cells appeared to enter the VNC state. Therefore, germfree mice were infected with O157 to examine the resuscitation of cells in the VNC state and the retention of
pathogenicity. O157 that originated in roe, but not patients, killed
mice and was isolated from the intestine. However, these isolates had
become sensitive to NaCl. O157 cells of roe origin incubated in normal media also killed mice and were isolated from the intestine, but they
also became transiently NaCl sensitive. We therefore propose that
bacterial cells might enter the VNC state under conditions of stress,
such as those encountered in vivo or in high salt concentrations, and
then revive when those conditions have eased. If so, the VNC state in
food is potentially dangerous from a public health viewpoint and may
have to be considered at the time of food inspection. Finally, the
establishment of a simple recovery system for VNC cells should be established.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Does Enterohemorrhagic Escherichia coli
O157:H7 Enter the Viable but Nonculturable State in Salted Salmon
Roe?
*
Corresponding author. Mailing address: Department of
Veterinary Microbiology, Obihiro University of Agriculture and
Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
Phone and fax: 81-155-49-5386. E-mail:
smakino{at}obihiro.ac.jp.
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