Physical characterization of bacterial biofilm polymer networks to determine the role of mechanics in infection and treatment




Kovach, Kristin N.

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Biofilms are communities of microorganisms that produce a matrix of extracellular polymers to surround and protect themselves from external forces in their environment. This communal lifestyle is incredibly beneficial for microorganism survival. Characterization of the mechanical properties of biofilms is a vital and understudied component of fully understanding these biological systems. In this dissertation, we break down the mechanical response of the Pseudomonas aeruginosa biofilm by its constituent polymers. These bacteria produce unique polymers to resist a variety of stresses. In the first part of this dissertation, using oscillatory bulk rheology, we characterize the viscoelasticity of biofilm polymer networks. Using genetically manipulated lab strains of P. aeruginosa, we isolate the mechanical response of each polymer by analyzing biofilms comprised primarily of one type of polymer. We find that the polymers have unique mechanical properties: some increase the yield strain and others increase elastic modulus. In strains of P. aeruginosa isolated from chronic infections, we find that the bacteria evolve to increase production of polymers that maximize the energy required to yield the matrix. In the second part of this dissertation, we work to mechanically compromise each of the polymers in the matrix. By attacking different matrix components, we learn more about the structural properties that give rise to mechanical properties as well as identify the most promising therapeutic treatments to break down biofilm infections. We find that specific enzymes are useful for decreasing yield strain of biofilms and increasing the diffusivity of the matrix. Decrease in yield strain means that biofilms will take less deformation before losing mechanical integrity, and the increase in matrix diffusivity means that current treatments such as antibiotics are more effective as the antibiotics can more easily reach the bacteria in the matrix to effectively kill them. This dissertation treats biofilms as polymer networks, divorcing the analysis from biological responses, in an attempt to well-characterize the understudied mechanical properties of biofilms. By approaching these systems from a physical standpoint, we are able to learn more about biofilms by breaking the mechanical response into constituent components, as well as learn about how enzymatic treatments alter biofilm properties.



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