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Evaluation of the RIDA®QUICK Verotoxin/O157 for the detection of Shiga toxin and Escherichia coli O157 in stool enrichment cultures

Abstract number: P1385

Mellmann A., Leidinger H., Sander P., Fischer R., Becker K., Bielaszewska M., Karch H.

Objectives: Shiga toxins (Stx) are the major virulence factors of enterohaemorrhagic Escherichia coli (EHEC), which can cause diarrhoea and the life-threatening haemolytic uraemic syndrome (HUS), the major cause of acute renal failure in childhood. The serogroup O157 is associated with 70–90% of all EHEC infections. The prompt detection of the pathogen is mandatory to start the adequate therapy. We therefore evaluated the new RIDA®QUICK Verotoxin/O157, which detects Stx and the E. coli serogroup O157 within 16 hours.

Methods: To evaluate the RIDA®QUICK Verotoxin/O157 (R-Biopharm, Darmstadt, Germany), in total 161 samples were analysed. These included 51 EHEC reference strains which represent a broad spectrum of 38 different serotypes, all known Stx subtypes (except for Stx2g produced by animal strains only), and 6 Stx-low producers. Furthermore, 98 stools, 8 isolates from these stools and 4 animal isolates from our routine clinical microbiological laboratory and from the consulting laboratory were investigated for the presence of Stx and O157. The results were compared to genotypic detection of Stx encoding genes (stx) and of the sfpA gene that is specific for a subset of EHEC O157 by PCR. To verify Stx production the Vero cell cytotoxicity assay was applied in addition.

Results: Of the 161 samples, 145 samples (90.1%) were correctly diagnosed using the RIDA®QUICK Verotoxin/O157 regarding Stx production and/or serogroup O157. The serogroup O157 alone was correctly detected in 157 samples (97.5%) and Stx production was correctly determined in 147 samples (91.3%) in comparison to PCR detection and the cytotoxicity assay. Sensitivity, specificity, positive and negative predictive values for Stx/O157 detections were 84.3/91.7%, 98.7/98.5%, 98.6/91.7%, and 85.6/98.5%, respectively. False negative results of Stx detection were mainly due to low Stx production in isolates (n = 3), to low amounts of EHEC in the stool enrichment broth (5), and to the presence of rare Stx subtypes (Stx2d, Stx2e) as sole Stxs (2). The low EHEC concentration also explained 2 false negative O157 results. In two further samples, false positive O157 results were detected.

Conclusion: Overall, the new RIDA®QUICK Verotoxin/O157 is a highly specific method to determine the presence of Stx and the serogroup O157 in stool enrichment cultures within 16 hours. Ongoing studies investigate the test performance in comparison to Stx targeting ELISA.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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