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United States Department of Agriculture

Agricultural Research Service

Research Project: NON-THERMAL AND ADVANCED THERMAL FOOD PROCESSING INTERVENTION TECHNOLOGIES Title: The survival of Shigella sonnei in frozen media and after ultraviolet treatment of ice and inoculated fish samples

item Rajkowski, Kathleen

Submitted to: Ice World Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 16, 2007
Publication Date: April 1, 2007
Citation: Rajkowski, K.T. 2007. The survival of Shigella sonnei in frozen media and after ultraviolet treatment of ice and inoculated fish samples. Ice World Journal. 9:14-23.

Interpretive Summary: Shigella sonnei can cause diarrhea type illnesses when contaminated water or food is consumed. If the pathogen contaminated water is used to manufacture edible ice, which is classified as a food by the FDA, it can survive and cross contaminate fish. This research was done to determine how long S. sonnei will survive frozen in various liquids at refrigerator-freezer and deep freezer temperatures. S. sonnei survived in all the liquids tested for 3 to 6 weeks, except for tap water which contained residual chlorine. When the residual chlorine was removed by heating, the S. sonnei survived in the tap water. Ultraviolet light treatment of the frozen pathogen suspension resulted in a 99.9 percent reduction. When the S. sonnei suspension was inoculated on frozen fish samples, ultraviolet light treatment resulted in a 99 percent reduction of the pathogen. The results of this study showed that S. sonnei can survive in frozen liquids and care must be taken to produce edible ice with pathogen free water. Ultraviolet light is an effective treatment to reduce surface contamination of fish providing a safer frozen product for the consumer.

Technical Abstract: Shigella sonnei is a water and foodborne pathogen that can cause dysentery, a type of diarrheic illness. Until recently, edible ice was not a food safety concern. However, Shigella spp. were reported to survive in ice and were epidemiologically linked to diarrheic illnesses. In order to determine the frozen state survival of S. sonnei F6129, several suspending liquids were used. The S. sonnei survived for > 3 wks while frozen in 0.85 and 2.0% saline, Butterfield and buffered peptone buffers, vegetable broth and autoclaved water stored either at -9 or -70 C. S. sonnei did not survive in filter sterilized tap water which contained residual chlorine, but did survive in the tap water when the residual chlorine was removed by either autoclaving or deionization. When S. sonnei was suspended in Butterfield buffer, which was then frozen, ultraviolet treatment (254 nm at 1.2 joules) was effective in reducing the bacterial counts by 3 log. UV treatment (1.2 joules) was also effective in reducing S. sonnei inoculated on frozen fish samples by 2 logs. UV treatment of S. sonnei inoculated on fresh fish resulted in no reduction of the pathogen, whereas the pulsed UV treatment resulted in a half log reduction. The results of this study showed that S. sonnei can survive for reasonable long periods of time (3 - 6 wks) while suspended in various ices. UV treatment may provide a decontamination intervention technique which would provide the consumer frozen fish with reduced pathogens and pathogen free edible ice.

Last Modified: 12/1/2015
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