Thesis Dissertation Defense

When single-celled bacteria exist in communities known as biofilms, they develop the ability to exhibit complex emergent properties such as social cooperation, resource capture, and enhanced survivability, the individual limitations of existence can be overcome which would otherwise be unlikely. Properties such as matrix production, quorum sensing, and coordinated lifecycle offers structural and functional advantages which makes them highly successful at evading destruction by antimicrobials and immune defenses. With few, if any, novel antibiotics in the clinical pipeline, there is a resurgence of interest in alternatives such as phage therapy, the practice of bacterial viruses known as bacteriophages that infect and lyse bacteria to treat infections.

In this thesis, we explore the understudied impact of phage titer on biofilm dynamics and outcomes. We determined that the biofilm developmental stage at the time of phage addition modulates its response. These responses vary as a function of the phage dose and can be broadly organized into four distinct classes. While nearly any phage dosage is sufficient to suppress biofilm formation in the first developmental stage, very little impact on biofilm outcome is evident for the dispersion stage even at high phage exposures. We also found that the early biofilm stage is increasingly suppressed by higher phage exposures, while paradoxically, the mature biofilm stage is enhanced by increasing phage exposure. Despite this apparently undesired outcome, the inhibition of biofilm dispersion in phage-treated samples could potentially minimize the further spread of infections to other locations. Additionally, for each of the response classes, high phage exposure halts the biofilm from transitioning into the next developmental stage of the biofilm lifecycle. Our results comprehensively demonstrate predictable biofilm outcomes versus phage dosage and biofilm age. These insights combined with the measurements of the rich spatiotemporal dynamics of the biofilms will facilitate future mathematical modeling and experimental efforts to test mechanistic hypotheses, while at the same time provide more perspective to guide clinical studies and phage-based personalized treatments. Other parts of this thesis furthers understanding and approaches to study neutrophil-biofilm interactions, phage lysis in spatially constrained environments, and anti-biofilm properties of a biocompatible hyaluronic acid based polymer brush system. Collectively, this dissertation provides insights on the advantages and limitations of phage, immune cells, and polymer brushes to inhibit, control, and eliminate biofilms.