Grant: Discovery Grants Program - Individual

Antibiotic resistance is now a well-documented problem worldwide. Other related issues such as bacterial persistence leading to antibiotic tolerance and evasion of the host immune defenses are less understood. Persistence by seemingly antibiotic-susceptible microorganisms is responsible for infection relapse and chronic manifestation of diseases. So-called difficult-to-treat infections (e.g., biofilms, infections of indwelling biomedical devices, lung infections in cystic fibrosis patients and recurrent infections in animals such as bovine mastitis) involve subpopulations of atypical bacteria that are not efficiently killed by antibiotics or the host immune system. Such atypical bacteria are called small-colony variants (SCVs) or Peristers depending on the mechanism by which they appear. The well-known pathogen Staphylococcus aureus can appear as a SCV. Compared to their commonly found normal counterparts, SCVs produce high amounts of protective biofilms, are tolerant to antibiotics and are capable of hiding and persisting within host epithelial cells. Many SCVs have mutations in the so-called respiratory chain that affect the enzyme (ATP synthase) responsible for producing the energy necessary for growth of the bacteria. Slow growing bacteria or dormant cells are tolerant to most antibiotics that usually kill actively growing bacteria. Fortunately, our research group has identified a natural product found in the tomato plant (tomatidine) that is able to kill S. aureus SCVs. The target of that new class of antibiotics is the ATP synthase. This discovery points to an essential function for the residual ATP synthase activity observed in SCVs. Unlike the S. aureus SCVs, other Persisters do not usually arise from mutations. There is abundant evidence that for example Escherichia coli persister cells arise from active mechanisms in response to a stress such as that caused by antibiotic exposure. An example of the mechanisms leading to E. coli persister cells involves the production of a bacterial peptide that sabotages its own respiratory chain and ATP production. This results in the generation of dormant cells tolerant to antibiotic action, a consequence similar to that observed in respiratory-deficient S. aureus SCVs. Based on our current understanding on how tomatidine acts on S. aureus SCVs, it is reasonable to suggest that Persisters may also be hypersusceptible to drugs inhibiting bacterial ATP synthase. The objectives of the proposed research is to characterize the mechanisms leading to the formation of SCVs and Persisters, to demonstrate that the ATP synthase is essential for these types of bacteria, and to demonstrate that the control and prevention measures we developed for S. aureus SCVs can be extended to other types of SCVs and Persisters. The low residual but apparently essential ATP synthase activity of SCVs might likewise represents the Achilles' heel of all persister cells from Gram positive or Gram negative pathogens.