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United States Department of Agriculture

Agricultural Research Service

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Research Project: Develop a New Microbiological Medium for Selective Cultural Enrichment of STEC

Location: Produce Safety and Microbiology Research

2012 Annual Report


1a.Objectives (from AD-416):
The objective of this cooperative research project is to develop a microbiological growth medium that is selective for Shiga toxin-producing Escherichia coli bacteria (STEC).


1b.Approach (from AD-416):
The principle of the STEC-selective medium is based upon competition between STEC and another microorganism. At least one recent scientific publication suggests the protozoan Tetrahymena thermophila is capable of killing E. coli that do not express Shiga toxin, while STEC can kill the protozoan. If STEC are present, they may be the only organisms capable of growth on the media. Developing the new media based on an existing E. coli selective medium will help in negative selection against non-E. coli toxin producers, which might otherwise compete against STEC and the protozoan. Additional selection may be applied in a modified pre-amplification culture, before plating on the new media. For validation, STEC will be spiked into foods and the Lower Limit Of Detection determined. Documents NFCA with Hardy Diagnostics. Formerly 5325-42000-043-08N (4/11).


3.Progress Report:

In FY12 a new culture method for detection of Shiga toxin-producing E. coli (STEC) was developed based on a highly selective medium that promotes the production of Stx by cultured STEC. This medium has now been commercialized. This medium facilitates the identification of STEC that are responsible for an estimated 265,000 infections each year in the US, including some fatalities. This medium can be incorporated into tests that would minimize the time needed for analysis, while enabling recovery of STEC from contaminated foods, thus enhancing the capabilities of industry and government to assure food safety. Research progress reported, addresses objective 1 of the parent project.


Last Modified: 7/31/2014
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