Alanning numbers of pathogenic bacteria are now resistant to multiple antibiotics. This problem is perhaps most pressing for two common hospital-borne pathogens, vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA). In the case of VRE, the resistance genes are encoded on large plasmids. Interestingly, through a survey of multiple VRE isolates we have discovered that these plasmids use toxin-antitoxin (TA) systems to maintain themselves in the bacterial host. In this system, if a plasmid-free daughter cell arises during cell division the labile antitoxin is degraded and the toxin kills the cell. We have pursued an antibacterial strategy based on the identification of small molecules that activate the latent toxin proteins in the bacterial cell;these compounds would thus induce cell death. Through surveys of VRE, MRSA, Staphylococcus sp., and P. aeruginosa, we have found that three particular TA systems are prevalent: CcdAB, RelBE, and MazEF. Through highthroughput cell-based screening we have now identified compounds that kill cells in a CcdAB-dependant fashion, and others that kill in a RelBE-dependent fashion. Described herein is a comprehensive plan designed to fully validate TA disruption as a tractable antibacterial target. This will involved chemical optimization of the lead compounds for CcdAB and RelBE, high-throughput screening to identify compounds that activate the toxins from these three TA pairs, and the use of peptides as TA disruptors.
The alarming rise of multi-drug resistant bacteria, combined with the severe slowdown in the discovery and development of novel antibiotics, has led to a situation where increasingly large numbers of infections simply cannot be treated with antibiotics. Described herein is an antibacterial strategy based on the activation of latent toxin- antitoxin systems that we have found to reside within bacterial cells.
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