Assessment of a real-time PCR for the detection and characterization of verocytotoxigenic Escherichia coli

The European Union Reference Laboratory (EU-RL) has produced guidelines for a real-time PCR for the detection of verocytotoxigenic Escherichia coli (VTEC). In this study, we validated the EU-RL assay on 545 strains of VTEC and evaluated the utility of the assay for the detection of VTEC from stool specimens. The validation study on cultures showed that the EU-RL VTEC PCR was 99.3% sensitive for the detection of vtx genes; only strains harbouring vtx2f genes were not detected. The assay was 100% sensitive and 100% specific for the detection of both the eae and O157 rfbE genes. In a prospective study involving 500 stool samples, the EU-RL VTEC PCR detected vtx genes in 12.4% of specimens, compared to 3.8% specimens found to be culture-positive for E. coli O157 using the Health Protection Agency national standard culture method. This study showed that the EU-RL VTEC assay was reliable and robust, and an effective rapid screening method for the detection of VTEC from stool specimens.