Characterization of hypochlorous acid as potent physiological antimicrobial

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Invasion of pathogenic bacteria elicit multiple defense mechanisms in host organisms. One very potent strategy that cells of the mammalian host defense system employ involves the production of high levels of hypochlorous acid (HOCl), the active ingredient of household bleach and a well-known, highly effective disinfectant. HOCl-production is used by neutrophils to kill off invading microorganisms, as well as by cells of barrier epithelia to control bacterial colonization. Recent studies demonstrated that HOCl causes the oxidative unfolding, inactivation and aggregation of countless essential proteins in bacteria, providing a first clue as to the mechanism by which bleach kills bacteria. Bacteria appear to have evolved vital strategies to protect themselves against HOCl-stress, allowing them to colonize host tissues and cause infections. Preliminary studies revealed that the uropathogenic E. coli (UPEC) strain CFT073, a strain known for its involvement in urinary tract infections, is substantially more resistant to HOCl-stress than commensal lab E. coli strains. Moreover, UPEC strains have the ability to form biofilms, which shield them against natural host defense systems, and further increase HOCl resistance. Aim of this study is now to identify and characterize selected UPEC-specific genes, which contribute to the enhanced HOCl-resistance of CFT073 in the planktonic state and/or in biofilms. We reason that by decreasing the HOCl-resistance of CFT073, we will inevitably decrease its pathogenicity. I will biochemically characterize selected UPEC-specific gene products, which contribute most strongly to the bleach resistance of CFT073, and determine their in vivo role during HOCl-stress by using the appropriate mutant strains. By using the respective deletion mutants in a urinary tract infection model, we will reveal which UPEC-specific gene products are essential for CFT073 pathogenicity. These proteins will serve as targets for future small compound screens. In summary, I will use a multifaceted biochemical and genetic approach to obtain a detailed understanding about how bacteria respond to and defend themselves against HOCl with the long-term goal to develop strategies that increase the sensitivity of pathogenic bacteria to HOCl.