Comparison of Shiga toxin-producing Escherichia coli detection methods using clinical stool samples

Molecular diagnostic tools capable of identifying Shiga toxin-specific genetic determinants in stool specimens permit an unbiased approach to detect Shiga toxin-producing Escherichia coli (STEC) in clinical samples and can indicate when culture-based isolation methods are required. It is increasingly recognized that clinically relevant STEC are not limited to the singular O157 serotypes, and therefore diagnostic assays targeting toxin-encoding determinants must be able to account for any genetic variation that exists between serotypes. In this study conventional PCR and four real-time PCR assays (HybProbe, TaqMan, SYBR Green, and LUX) targeting the stx1 and stx2 Shiga toxin coding sequences were used to identify STEC in enriched stool samples (n = 36) and a panel of O157 and non-O157 strains (n = 64). PCR assays targeting stx1 and stx2 had variable specificity and sensitivity values with enriched stool samples. Molecular assays using DNA from pure cultures revealed that some primers were not sensitive to all stx2 variants. This evaluation concluded that the TaqMan-based probes were most appropriate in high throughput clinical diagnostic laboratories in consideration of cost, turn around time, and assay performance.