830. Comparison of Three Different Methods for Detection of Shiga Toxin-Producing Escherichia coli in a Tertiary Paediatric Care Center
Session: Oral Abstract Session: Advances in Diagnostics
Saturday, October 22, 2011: 8:15 AM
Room: 151AB
Background:  Shiga toxin-producing Escherichia coli (STEC) is a common cause of food-borne gastroenteritis, hemorrhagic colitis and may lead to hemolytic uremic syndrome (HUS). HUS is the major cause of acute renal failure in pediatric patients. STEC are characterized by the presence of at least one of the two types of Shiga toxins, Stx1 and Stx2. The first serotype of STEC identified was O157:H7 (O157 STEC) but at least 150 other serotypes are human pathogens. However, O157 STEC is the only serotype easily identified by culture on sorbitol MacConkey agar (SMAC). To optimize the recovery of non-O157 STEC, the CDC recommends since 2009 to screen for Shiga toxins all specimens submitted for enteric pathogens detection. The objective of this study was to compare the performance of SMAC with an enzyme immunoassay (EIA) and a real time PCR for the detection of STEC in our pediatric institution.

Methods: Between June and September 2009, we tested all stool samples from pediatric patients sent to our laboratory to rule out bacterial enterocolitis. The usual workup, including SMAC, for common enteric pathogens was done, and a MacConkey broth was added. After overnight enrichment of the broth, the STEC screening was performed by EIA Premier EHEC (Meridian) and a real time home brew PCR targeting stx1 and stx2. For EIA positive samples, the type of Shiga toxin was determined by the ImmunoCard STAT! EHEC (Meridian). For specimens with discrepant results, positive by PCR or EIA and negative by SMAC, another PCR targeting different gene sequences was done.

Results:  On 632 samples tested, SMAC identified 5 O157 STEC. EIA recovered 6 positive samples, 3 distinct from SMAC, but failed to detect 2 O157 STEC. Finally, the PCR detected 21 stool specimens exhibiting at least one type of Shiga toxin. All the discrepant results had been confirmed positive by the second PCR.

Conclusion: In our institution, we found that the adjunct of a PCR targeting genes coding for Shiga toxin over SMAC significantly increase our detection rate of STEC. The sensitivity of the EIA was not as high as reported in the literature and raised the concern to miss O157 STEC. It was therefore decided to perform a PCR on each stool sample sent to our laboratory for detection of enteric pathogens, in addition to the usual workup.

Subject Category: D. Diagnostic microbiology

Emilie Vallieres, MD, Clinical Microbiology and Infectious Diseases, CHU Sainte-Justine, University of Montreal, Montreal, QC, Canada, Maude Saint-Jean, MD, Microbiology and Immunology, and Pediatric Infectious Diseases, CHU Sainte-Justine, University of Montreal, Montreal, QC, Canada and Fabien Rallu, PhD, Microbiology and Immunology, CHU Sainte-Justine, Montreal, QC, Canada


E. Vallieres, None

M. Saint-Jean, None

F. Rallu, None

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