Investigating Novel Antimicrobial Strategies in vitro and in Murine Models of Infection

Thesis (Ph. D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2015.Novel approaches are needed for the therapeutic intervention of microbial pathogens. This research describes the use of human immunodeficiency virus (HIV-1) and Staphylococcus aureus (SA) as model organisms to test three novel antimicrobial strategies. First, we designed synthetic nanoparticles intended to sterically interfere with the ability of a recently described cationic amyloid fibril, the semen derived enhancer of viral infection (SEVI), to promote HIV-1 infection in vitro. These amyloid-binding nanoparticles bound SEVI, and potently reduced SEVI mediated HIV-1 infection in a manner consistent with a steric effect. Second, we tested the hypothesis that SEVI may possess antibacterial activity, as has been reported for other amyloidogenic peptides. SEVI did not directly inhibit bacterial growth, but it did bind bacteria, including SA, and enhanced their phagocytic uptake by macrophages. We then generated self-assembling synthetic cationic peptides with similar charge-to-mass ratio to SEVI and investigated their antimicrobial properties – which were found to be very similar to SEVI. Finally, we examined SEVI’s antimicrobial properties using a mouse model for Neisseria gonorrhoeae infection of the vaginal tract, and found that SEVI accelerated bacterial clearance in this model. Collectively, these data suggest that amyloid cationic fibrils have potential as antimicrobial agents. Third, we tested the antimicrobial effectiveness of rationally designed drug combinations that act on bacterial RNA metabolism. To do this, a high-throughput screen was conducted to identify anti-staphylococcal small molecules that target tRNA synthesis. This identified a previously unrecognized activity of the antibiotic, neomycin, which we then tested for its ability to enhance the activity of mupirocin, which also acts on tRNA metabolism. In a murine model for nasal infection with SA, mice treated with combination therapy had improved bacterial decolonization rates and reduced development of mupirocin resistance. Collectively, we conducted proof-of-concept studies that validate three new antimicrobial approaches: (i) nanoparticles that sterically interfere with virus binding, (ii) cationic amyloid fibrils, and (iii) additive combinations of small molecules that block bacterial RNA metabolism. This work points to new directions in treating deadly microbial infections