Evaluation of the Duopath Verotoxin Test for Detection of Shiga Toxins in Cultures of Human Stools

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Abstract
The Duopath Verotoxin test (Merck KgaA, Darmstadt, Germany) is a newly developed immunochromatographic test for the confirmation of Shiga toxin (Stx)-producing Escherichia coli (STEC) strains from food products. This test detects both Stx 1 (Stx1)-positive and Stx2-positive samples individually with the same device. By modification of the original protocol, the present study evaluated its performance and feasibility for clinical application with human stool samples, consisting of 41 frozen samples known to contain STEC isolates (O157:H7 and non-O157 serotypes) and 250 fresh specimens. The test specimens were polymyxin B extracts of colony sweeps taken from overnight sorbitol-MacConkey agar cultures of stools containing STEC isolates and other bacteria. All 41 frozen STEC-positive stool samples were positive by the Duopath Verotoxin test, as were 2 fresh stool samples with culture-confirmed STEC O157 infection. Thus, 100% sensitivity and no false-positive results were obtained when the Premier EHEC assay (Meridian Bioscience, Cincinnati, Ohio) was used as the “gold standard.” The Duopath Verotoxin test is simple to perform and easy to interpret, providing a turnaround time of 24 h. Despite its original intended use, the Duopath Verotoxin test has a great potential for clinical application.