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Shiga toxin -producing Escherichia coli (STEC) is a public life-threating pathogen and another contagious food-borne disease with a wide spectrum of severity, from watery diarrhea and hemorrhagic colitis to Hemolytic Uremic Syndrome (HUS).(56) Seven serogroups are associated with hemorrhagic colitis (HC) and Hemolytic Uremic Syndrome related to entero-hemorrhagic E. coli (EHEC) (57). There are over 400 non-O157 serotypes associated with human disease (58). The most dangerous feature of STEC infections is the production of potent Stxs, immunological non-cross reactive toxins, categorized as Stx1 and Stx2. Both toxins cause disease in animal, but humans HUS is associated with Stx2. The Stx2e causes edema disease in neonatal piglets leading to fatal outcomes and economic losses (59, 60). This sever toxin consists of an enzymatically active A subunit and five B subunits that bind to a glycolipid receptor (61). Up to now, there isn’t any available vaccine or e?ective therapy against infection for human use and treatment is limited to fluid replacement. Furthermore, antibiotics treatment has a progressive effect on STEC infection into HUS and drug resistance is inevitable. (62). So, there is an urgent need for new effective treatment options. At present, anti-Stx mAb exhibit successful results in animal models (63, 64) and in clinical trials. However, complicated process of production and the high cost of optimization of mAbs are tremendous (65, 66). Jacqueline et al reported VHH- based neutralizing Ab effective in patients suffering from STEC.
Such heterodimer VHH antitoxin consists of two Stx1or Stx2 linked together provided more neutralizing activity of Stx than two separate monomers in cell-based assays and in vivo mouse models(67). In order to improve VHH half-life, two copies of Nb were fused to anti-human seroalbumin VHH, (2vb27)2-SA. Nb construct showed protective activity against toxic effects of Stx with increased neutralization activity due to avidity effect and absence of Fc fragment (68).
Challa et al used RETA APMs by the SELEX method to detect shiga toxins; they found that SELEX, p-SELEX and M-SELEX products retrieved from RNA library were able to bind stx2 not to Stx1. So, these aptamers could be employed for stx2 diagnosis in future (69).

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