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United States Department of Agriculture

Agricultural Research Service

Title: A Multiple Protocol to Improved Diagnosis and Isolation of Shiga toxin-Producing Escherichia coli (STEC) from Human Stool Specimens

item Shelton, Daniel
item Park, C.
item Karns, Jeffrey

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 2/17/2007
Publication Date: 5/21/2007
Citation: Shelton, D.R., Park, C., Karns, J.S. 2007. A multiple protocol to improved diagnosis and isolation of shiga toxin-producing escherichia coli (stec) from human stool specimens. 107th Annual Meeting of the American Society for Microbiology, May 21-25, 2007, Toronto, Canada.

Interpretive Summary:

Technical Abstract: Many enterohemorrhaegic colitis caused by STEC are undiagnosed. Even when properly diagnosed, a minimum of two weeks is required to identify an outbreak. We evaluated the use of multiple protocols to improve diagnosis, isolation and characterization of STEC strains. The IFH performed the initial detection of STEC directly from stools, sorbitol-MacConkey agar (SMAC) and MacConkey broth. The EIA devices applied were Premier EHEC (Meridian Biosciences) and OIA®SHIGATOX (Inverness Meidcal-BioStar). The real-time PCR was conducted by the USDA/ARS on enriched cultures from broth media: EC, Minimal Lactose (MLB), and MacConkey broth (MAC) media. Among 18 stool samples received by IFH for analysis, 16 were toxin-positive, which yielded 8 sorbitol-negative O157:H7 and 5 sorbitol-positive, non-O157 STEC from SMAC. The remaining 5 samples required enrichment on EC, MLB and/or MAC broth due to a failure to isolate STEC from SMAC. All 5 enriched samples were toxin-positive (including the two samples that were previously toxin-negative from direct stool). Two O157:H7 and one non-O157 STEC were isolated. The two remaining enriched samples did not yield isolates; however, based on PCR analysis both enriched samples contained non-O157 EHEC at extremely low concentrations. Based on PCR analysis of non-O157 strains, 3 strain types were identified. Samples from 3 patients, which were received within 2 days of one another, had a similar gene profile--- eae- and stx1-negative, and stx2-positive. The uniqueness of this gene profile suggests that these patients were most likely infected with a common strain from a common source. Our results indicate that a multiple protocol approach is necessary to reliably diagnose and isolate STEC strains. In addition, PCR analysis may allow for rapid identification of localized STEC outbreaks. All of these protocols are suitable for use in clinical labs, and if used routinely, would allow for a higher rate of diagnosis and more rapid identification of outbreaks.

Last Modified: 07/28/2017
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