A New Immunoassay for Detecting All Subtypes of Shiga Toxins Produced by Shiga Toxin-Producing E. coli in Ground Beef

BACKGROUND: Shiga toxin (Stx) is a common virulence factor of all Shiga toxin producing E. coli (STEC) that cause a wide spectrum of disease, including hemorrhagic colitis and hemolytic uremic syndrome (HUS). Although several commercial kits are available for detection of Stx produced by STEC, none of them are capable of recognizing all subtypes of Stxs, which include three subtypes of Stx1 and seven subtypes of Stx2. METHODS AND FINDINGS: New monoclonal and polyclonal antibodies against Stx1 and Stx2 were developed. A universal sandwich ELISA capable of detecting all known subtypes of Stx1 and Stx2 was established using a pool of newly developed antibodies. To precisely monitor the sensitivity of the assay for each subtype of Stxs, recombinant toxoids were created and used as standards in ELISAs. Because of the high affinity of the antibodies incorporated, the ELISA assay is highly sensitive with a limit of detection for the different subtypes of Stx1a and Stx2a between 10 and 50 pg/mL in phosphate buffered saline (PBS). The assay was also able to identify STEC based on the production of Stxs using the supernatants of culture fluids or even single colonies on agar plates without lengthy enrichment in liquid medium. When applied to ground beef samples, this newly developed ELISA was capable of distinguishing beef samples spiked with a single bacterial cell. CONCLUSIONS: A highly sensitive and universal assay for all subtypes of Stx1 and Stx2 was developed. It has significantly improved upon the current technologies by avoiding false negative results due to the narrow detection range of the assay. The assay developed in this study can be useful for prompt detection of new and emerging serotypes and screening ground beef samples for contamination of STEC at an early stage in the food supply chain, thus avoiding the need for possible recall.