Infective endocarditis, a condition in which bacteria grow in a biofilm-like state on the valves of the heart, is a deadly complication of bloodstream infections. Enterococcus species are responsible for 30% of healthcare- acquired endocarditis. When caused by multi-drug resistant strains, such as vancomycin-resistant enterococci (VRE), infective endocarditis is nearly untreatable and uniformly fatal. The CDC considers VRE a serious threat and estimates 5,400 VRE-related deaths and over $500 million in associated healthcare costs in 2017. A major risk factor for the development of enterococcal endocarditis and other infections is prior treatment with cephalosporin antibiotics. The two most clinically relevant species of Enterococcus, E. faecalis and E. faecium, are intrinsically resistant to cephalosporins. Treatment with cephalosporin antibiotics allows commensal enterococci to proliferate and disseminate to the bloodstream, a prerequisite for infection of the heart valves. The goal of this project is to further our understanding of molecular mechanisms of cephalosporin resistance in enterococci. This understanding will enable development of new therapies that both reduce the occurrence of enterococcal infections and improve treatment options to overcome recalcitrant endocardial infections. Specifically, a novel link will be investigated between two known cephalosporin resistance determinants, IreK and MurAA. IreK is a kinase that is thought to sense and respond to cell wall stress, including that caused by inhibition of peptidoglycan crosslinking upon cephalosporin treatment. However, the targets of IreK signaling that facilitate this response, and ultimately cephalosporin resistance, are largely unknown. MurAA, an enzyme that catalyzes the first committed step in peptidoglycan synthesis is also required for cephalosporin resistance. The central hypothesis of this project is that MurAA is a downstream target of IreK signaling, such that regulation of MurAA is one mechanism by which IreK controls cephalosporin resistance. Preliminary evidence suggests that this regulation is mediated by the known IreK-phosphorylation substrate, IreB. This hypothesis will be addressed in two aims.
Aim 1 will determine how IreB and IreK signaling impact functions of MurAA.
Aim 2 will identify MurAA interaction partners and determine the functional consequences of these interactions. Preliminary data suggest that a protein-protein interaction is important for either facilitating or regulating functions of MurAA. This work will be conducted at the Medical College of WI under the sponsorship of Dr. Christopher Kristich. The sponsor and institution are well-equipped to provide resources and support for this fellowship. In collaboration with the sponsor, the candidate has designed a training plan that complements this project. The training plan supports development of broad technical, communication and mentoring skills and encourages the professional development of the candidate. Development of these competencies will catalyze a successful career for the candidate as a well-rounded, independent scientist investigating microbes in human health and disease.
Healthcare-acquired bloodstream and endocardial infections caused by Enterococcus species are associated with high mortality rates and healthcare costs and dwindling treatment options due to the emergence of multidrug-resistant strains. Elucidating antibiotic resistance mechanisms in enterococci is critical to prevent these often-fatal infections and expand our repertoire of treatment options. This study will provide insight into a mechanism of intrinsic cephalosporin resistance in enterococci by investigating the role and regulation of a peptidoglycan synthesis enzyme known to be required for this resistance.
