Clostridioides difficile is the leading cause of antibiotic-associated diarrhea in the hospital and long term health care settings. In addition to the patient toll, the treatment-associated costs of C. difficile infections to the United States healthcare system have been estimated at $5 billion. Although the rate of C. difficile infection in the United States is rising, surprisingly little is known about the mechanisms by which C. difficile spores maintain their extreme resistance properties. C. difficile is believed to be acquired by the host in the form of a dormant spore which contaminates the nosocomial environment. In other organisms, a significant amount of resistant to UV and genotoxic chemicals is provided by the small acid soluble proteins (SASPs). SASPs are thought to nonspecifically bind to DNA and alter its form to prevent the formation of thymidyl-thymidine adducts (thymidine dimers) upon UV exposure. These proteins also provide resistances to reactive oxygen, acids, crosslinking agents and minor resistance to heat. In C. difficile, however, nothing is known about how these important proteins contribute to the C. difficile spore resistance spectrum. C. difficile SspA provides resistance to UV but SspA & SspB play a role in spore formation. The C. difficile ΔsspA ΔsspB double mutant strain does not produce mature spores suggesting that these SASPs regulate, at some level, the sporulation program. This application will analyze the impact of SASPs on spore biology in three aims. Aim 1 investigates how SspA & SspB contributes to spore formation and how the C. difficile SASPs protect the C. difficile genome from UV damage. Aim 2 investigates mechanisms by which the SASPs contribute to spore formation. Aim 3 investigates how the protease that degrades the SASPs during germination is regulated and its spectrum of activity in the spore. Successful completion of these aims will thoroughly characterize the impact of SASPs on spore resistance and lead to the future design of agents that can clean a contaminated environment.

Successful completion of the experiments listed in this proposal will characterize, in detail, the Clostridioides difficile spore small acid soluble proteins. These proteins contribute to the extreme resistance properties that are characteristic of endospores, C. difficile included. By understanding how C. difficile spores maintain their resistance to genotoxic chemicals / treatments, a better strategy to reduce their burden in the healthcare environment can be designed.