| Summary: | Shiga toxin (Stx) producing E. coli (STEC) infections represent an important public health problem given the severity of the disease and sequelae associated to it. Since the use of antibiotics enhances the virulence of STEC, new therapeutic strategies are urgently required. Thus, the main aim of this project is the study of small molecules that are able to block expression of Shiga toxin in Escherichia coli O157:H7. The genes encoding Stx are located on temperate lysogenic phages integrated into the bacterial chromosome and expression of the toxin is generally coupled to phage induction through the SOS response. We aimed to find new compounds capable of blocking expression of Stx type 2 (Stx2) as this subtype of Stx is more strongly associated with human disease. High-throughput screening of a small-molecule library identified a lead compound that reduced Stx2 expression in a dose-dependent manner. We show that the optimized compound interferes with the SOS response by directly affecting the activity and oligomerization of RecA, thus limiting phage activation and Stx2 expression. Our work suggests that RecA is highly susceptible to inhibition and that targeting this protein is a viable approach to limiting production of Stx2 by EHEC. This type of approach has the potential to limit production and transfer of other phage induced and transduced determinants. As a result of the successful identification of a small molecule capable of inhibiting Stx2 expression in E. coli O157:H7, an additional high-throughput screening (HTS) of small molecules was performed. Two new compounds with activity against Stx2 production were successfully identified and characterised in biological assays. Finally, we describe the use of a small molecule with previously reported anti-quorum sensing activity. Our findings suggest that the compound furanone C-30 blocks stx expression in vitro.
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