Novel monoclonal antibodies against Stx1d and 1e and their use for improving immunoassays

Shiga toxins (Stxs) are major causative agents for bloody diarrhea and hemolytic uremic syndrome, a life-threatening disease in humans. No effective treatment is available. Early detection of Stxs in clinical samples is critical for disease management. As bacteria evolve, new Stxs are produced; therefore, methods used to identify them need to be improved as well. In this study, new monoclonal antibodies (mAbs) against Stx1d and 1e were developed and used to improve a commercial Stx1 kit. Incorporation of the new mAbs into the Abraxis Stx1 kit not only increased the assay sensitivity to Stx1d, but the assay was conferred the ability to detect Stx1e, a newly identified subtype of Stx1 produced by an atypical Stx-producing bacterial strain, Enterobacter cloacae M12X01451, isolated from a clinical specimen. This toxin was not detectable using existing commercial kits. The signal to noise ratio (s/n) of the new assay was increased 3-fold for Stx1d, and 44-fold for Stx1e at toxin concentration of 10ng/mL. The limit of detection (LOD) was 10pg/mL for Stx1a, and 100pg/mL for Stx1c, 1d and 1e. When used for bacterial strains, the sensitivity of the new assay was improved 2.5- to 60-fold depending on subtypes produced. In summary, high affinity mAbs against Stx1d and 1e were developed and incorporation of these mAbs into the Stx1 kit significantly enhanced the assay sensitivity and broadened the subtype-specificity. This improvement should be useful for reducing product recalls and disease mistreatment due to failures of detecting less common but clinically important subtypes of Stxs.