Development and evaluation of a PCR-microplate capture hybridization method for direct detection of verotoxigenic Escherichia coli strains in artificially contaminated food samples

For the purpose of detecting, directly in food, veroxigenic Escherichia coli, a microplate hybridization method for the detection of PCR products from the SLT I and SLT II genes, was developed and evaluated. Two pairs of primers and two probes, specific for the SLT I gene and for the SLT II gene, were designed and tested. For the strains containing both genes, two PCR products of different molecular weights were obtained, whereas when only one gene was present only one fragment resulted from PCR. The use of the biotin-labeled probes allowed the immobilization of the PCR products in the microtiter plate wells and by this means their detection was possible using an ELISA-based technique. Forty artificially contaminated and fifty naturally contaminated food samples were analyzed by using the PCR–microplate hybridization technique developed in this study. All the artificially contaminated food samples were positive, independently of the number of cells inoculated before the enrichment step, whereas the naturally contaminated food samples were all negative.