Evaluation of the VTEC-Screen "Seiken" test for detection of different types of Shiga toxin (verotoxin)-producing Escherichia coli (STEC) in human stool samples.

An immunoassay for in vitro detection of Shiga (Vero) toxins Stx1 and Stx2 (VTEC-Screen "Seiken") was compared with the verocell toxicity test (VCA) and an stx-gene specific PCR for detection of Shiga toxin-producing E. coli (STEC) from 234 human stool samples selectively enriched on sorbitol-MacConkey (SMAC) agar. Culturable STEC were isolated from 59 (25.2%) of the 234 stool specimens and were found to be distributed over 20 different O-serogroups. Fifty-three (89.8%) of the 59 STEC-positive samples were identified with the VTEC-Screen compared to 55 (93.2%) with the PCR and 58 (98.3%) with the VCA. A possible false positive reaction with the VTEC-Screen was obtained with one sample and five samples showed aspecific reactions with both the test- and the control latex. The VTEC-Screen detected all samples which contained Stx1 producing strains (77.9% of STEC-positive samples) but was negative with six samples (10.2%) which contained Stx2 and/or Stx2 variant producers, although secondary enrichment of on brain-heart infusion agar detected three of these to improve the detection rate to 94.9%. Examination of reference strains encoding different genotypes of stx(1) and stx(2) indicated that certain variants of Stx2 reacted poorly (Stx2d-Ount, Stx2e and Stx2ev) or not at all with the VTEC-Screen. Overall, however, the test was found to be accurate, rapid and easy to perform, thus being suitable for the routine screening of clinical stool specimens for STEC.