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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

Authors
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
item Carter, John

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: 12/19/2014
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