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United States Department of Agriculture

Agricultural Research Service

Research Project: Technologies for Detecting and Determining the Bioavailability of Bacterial Toxins

Location: Foodborne Toxin Detection and Prevention

Title: Development of biphasic medium for detection of Shiga toxin producing E. coli using Tetrahymena thermophila

item Salvador, Alexandra
item Clotilde, Laurie -
item Bernard Iv, Clay
item Lauzon, Carol -
item Crowe, Chris -
item Lin, Andrew -
item Hartman, Gary -
item Lau, David -

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 17, 2012
Publication Date: N/A

Technical Abstract: E. coli O157 has long been the leading cause of major foodborne STEC outbreaks but recently non-O157 STECs are increasingly implicated. Selective media for E. coli O157 are commercially available but none detect non-O157 STEC. Currently, regulatory agencies screen for non-O157 STECs by enriching foods overnight, spreading aliquots onto Levine’s eosin methylene blue and chromogenic agar plates, and testing colonies by PCR or agglutination assay until a positive colony is recovered. This process can be lengthy (2-21 days). Here we describe development of a highly selective medium based on expression of Shiga toxin (Stx). Earlier, it was shown that when Tetrahymena thermophila protozoa are co-cultured with non-STECs, T. thermophila use the bacteria as a food source, but when co-cultured with STECs, T. thermophila are killed after 6 hours. Using a Shiga-toxin inducing broth developed by a commercial partner (Hardy Diagnostics) we were able to further evaluate this model. Culturing STEC in this broth enhanced production of Stx, and after a 2 hour co-incubation with T. thermophila, all T. thermophila were killed. We are currently exploring the development of a biphasic system to identify STEC. This system will be comprised of a thin liquid overlay of T. thermophila on a solid agar similar in composition to existing commercial E.coli selective medium. Ultimately the goal is to develop an assay sufficiently sensitive to detect one ID50 of STEC in a single serving of food. This system would accelerate identification of STECs, facilitate laboratory efforts such as molecular serotyping, reduce the time to issue a product recall, and could be used by regulatory agencies.

Last Modified: 9/10/2014
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