Grant: Project Grant - PA: Antimicrobial Resistance (Bridge Grant)

The use of lytic viruses called bacteriophages (or simply phages) to kill multidrug resistant bacteria such as the human pathogen Clostridioides difficile (Cd) has gained a lot of interest recently. The manipulation of the microbiome with genetically-engineered phages to restore health is also attracting a lot of attention. However, despite 100 years of phage research, important gaps in our understanding of the molecular steps leading to a successful viral infection still exist. Filling these gaps is essential for the future development and approval of phage-based biotherapeutics. The most critical step of a phage infection cycle is recognition of a bacterial receptor. This lock-and-key interaction is highly specific, the lock being a bacterial surface component and the key being a phage protein. We recently identified SlpA, the main protein composing the outer layer of Cd cells, as being an important phage receptor. Also, using bioinformatics and cryo-electronic microscopy (cryo-EM) reconstruction of whole phage particles, we identified phage proteins involved in SlpA recognition. Most importantly, we successfully engineered a phage tail to make it bind to and infect a different host in a SlpA-dependent manner. Our goal is now to describe with an unprecedent level of detail phage-host interactions in Cd, with emphasis on the molecular interactions between phage tail proteins and SlpA. To do this, we will use bacterial and phage genomics, cryo-EM phage reconstruction, genetic engineering of SlpA and phage proteins, viral functional assays, and a mouse model of Cd infection. These exciting results will deepen our global understanding of phage-host interactions and, ultimately, will pave the way to the rational design of therapeutic phages to fight Cd infections.