Beyond Antibiotics: New Drugs Blocking Type Three Secretion

On acceptance of his Nobel Prize for the discovery of Penicillin in 1945, Sir Alexander Fleming warned of the threat of antimicrobial resistance (AMR), stating ‘there is a danger that the ignorant man may easily underdose himself and by exposing his microbes to non-lethal quantities of the drug, make them resistant’. By 2019, Fleming’s fears were realised, with 1.27 million deaths directly attributed to AMR globally. Bacteria have the ability to rapidly evolve resistance and as a result, we have consistently observed resistance to antibiotics arising shortly after their introduction. Therefore, we must investigate therapies which are “evolution-proof” to improve the longevity of drugs and improve patient outcomes. In this proposal, I outline my plans to investigate antivirulence (AV) drugs as novel anti-infective agents. These differ from traditional antibiotics as their mechanism is not to kill or inhibit the growth of the infecting bacteria, but instead to prevent pathogens from causing disease within the host. One potential target for AV therapies is the Type III Secretion System (T3SS), a molecular syringe which delivers effector proteins to host cells and facilitates epithelial cell attachment in enteric pathogens. This is a shared virulence factor across pathogens such as Salmonella, Shigella, Enteropathogenic and Enterohaemorrhagic Escherichia coli. Targeting of virulence factors such as the T3SS, which are not essential for survival, results in decreased selective pressure for the evolution of resistance. For enteric pathogens, the narrow spectrum of activity may reduce disruption to the native gut microbiome and reduce recurrent infections linked to antibiotics. I aim to apply the AV concept to a significant global pathogen; Shiga-toxin-producing E. coli (STEC). These are acute enteric pathogens which are responsible over one million cases of foodborne disease worldwide. These pathogens are completely reliant on the T3SS to colonise their host, highlighting them as prime candidates for targeting by AV drugs. In my previously published work, I investigated aurodox – a natural product of the soil bacterium Streptomyces goldiniensis – as a novel inhibitor of the T3SS. This work has demonstrated that aurodox transcriptionally downregulates the expression of the T3SS in EHEC, and the SPI-2 T3SS of Salmonella Typhimurium). I have worked alongside experts in infection biology to establish a bespoke murine model of EHEC disease pathology and have shown that aurodox prophylactically protects mice against the infection. In this fellowship, I will expand the testing of aurodox beyond the single serotype previously tested (E. coli O157:H7) to the ‘big six’ circulating STEC serotypes worldwide. I postulate that these experiments will demonstrate the robustness of aurodox, and demonstrate its translational potential for use as an AV therapy in the clinic. I will use synthetic biology to enhance the pharmacological properties of aurodox before testing the resulting compounds in vitro, an ultimately, I a murine model of STEC. Finally, I will expand my study of AV molecules beyond aurodox by identifying bioactive bacterial metabolites with therapeutic potential from unexplored environments. I will use a combination of deep metagenomic sequencing and traditional culture-based techniques to study the actinobacterial population of the bovine gut, which is the reservoir of STEC. These experiments will form the foundations of my own unique research area as I transition to independence. These objectives contribute to the overarching goal of developing novel treatments for enteric pathogens with limited treatment options.