Functional Role of the Enterococcal Polysaccharide Antigen

Enterococci represent one of the leading causes of infections among hospitalized patients and residents of long-term care facilities. In the USA, there were over 50,000 cases of enterococcal infections in 2017, with ~10% fatality rate. The majority of infections are caused by Enterococcus faecalis and E. faecium, which include bacteremia, urinary tract and surgical sites infections, and endocarditis. E. faecalis and E. faecium display high levels of natural and acquired antibiotic resistance that severely limits the treatment options. In Enterococci, one of the major components of cell wall is the Enterococcal Polysaccharide Antigen (EPA). The recently solved structure of EPA polymer consists of a polyrhamnose backbone decorated with wall teichoic acids. While the putative mechanism of EPA biosynthesis has been proposed, the critical steps of this mechanism remain poorly defined. The goal of this application is to decipher the mechanism of initiation of polyrhamnose and wall teichoic acid assembly. In addition, we will examine the role of EPA in the resistance mechanism to daptomycin, the antibiotic of last resort. We will utilize a combination of genetic, analytical and biochemical methods to answer these questions. The proposed experiments will provide a better understanding of cell wall biogenesis in Enterococci to enable the development of alternative approaches to treat drug-resistant infections. EPA has been proposed as a vaccine candidate whereas the enzymes of the EPA biogenesis represent attractive drug targets, therefore the proposed studies will have implication for the vaccine and drug development.