Following the current ISO method (ISO/TS 13136), not all variants of the stx2 pathogenicity gene are detected, particularly stx2f. Differences in important serotypes exist between Europe and the United States. ISO/TS 13136 requires five serotypes (O26, O103, O111, O145 and O157). Moreover, there will be an extension of regulation (EC) 2073/2005 specifically for sprouts, which requires these five as well as O104.
Purpose: To evaluate the specificity (inclusivity and exclusivity), sensitivity, and robustness of the ISO/TS 13136 method (a PCR-based method) for STEC screening and serotype identification in comparison to the foodproof STEC Screening and O-group Identification Kits.
Methods: ISO primary enrichment for STEC testing was performed. Enrichments were then tested using ISO/TS13136 described PCR-based method or PCR-based STEC screening kit, which involved DNA extraction from the primary enrichment followed by real-time PCR. The serotypes of STEC-positive samples were then determined using the O-group identification kit.
Results: The sensitivity and robustness of the screening and O-group identification kits fulfill requirements set forth by ISO/TS13136. However, the specificity of the screening kit was superior due to its detection of more Shiga-toxin variants, such as stx2, and the O-group Identification Kit determined 3 more O-groups than the ISO/TS 13136 method currently requires.
Significance: The combination of the foodproof STEC Screening and O-group Identification Kits provided the ability to detect and identify all eight serotypes simultaneously and reduce the time-to-result.