Biophysics of phage-bacteria evolutionary interactions in context of patient therapy

The rise of antibiotic resistance warrants exploration of novel approaches for addressing difficult to treat bacterial infections. Phage therapy uses bacteria-specific viruses (bacteriophages) to target and kill infecting bacteria, but evolution of phage-resistance compromises efficacy of patient treatment. We use phage "steering" of bacterial evolution to overcome this problem; administering phages that bind to virulence factors on the cell surface exerts selection for target bacteria to evolve phage-resistance by modifying (or losing) the binding structures (evolutionary trade-off). This talk presents our method for high-throughput quantification of phage adsorption to host cells, to test hypotheses concerning evolved changes in phage-bacteria interactions. We use fluorescence microscopy-based assays and particle-tracking algorithms to obtain single phage trajectories from videos recorded with high spatiotemporal resolution. From thousands of trajectories, we obtained histograms of the "dwell time" that a phage spends near bacterial cells, likely exploring the surface. We propose an updated model of the biophysics of phage adsorption, which establishes a new framework for quantifying the dynamics and stochasticity of evolved interactions between viruses and host-cell surfaces as bacteria change to resist phage attack. These in vitro studies are used to examine evolved changes in phage-bacteria interactions for microbes isolated longitudinally from patient samples before, during and after emergency phage therapy treatments.