When bacteria attach to a surface and grow as a biofilm they are protected from killing by antibiotics. Biofilm formation is increasingly recognized as a factor in the persistence of varied infections. The goal of this project is to complement ongoing experimental investigations of antibiotic resistance in biofilms by developing the first comprehensive, phenomenological model of biofilm reduced susceptibility to killing by antibiotics. An existing mathematical model of biofilm development will be expanded to include four hypothesized protective mechanisms. These mechanisms address retarded antibiotic penetration, reduced metabolic activity or growth in parts of the biofilm due to local nutrient depletion, stress response activation by some biofilm bacteria, and differentiation of some biofilm cells into a dormant persister state analogous to spore formation. The model will be improved by developing mathematical expressions for the release of cells from the biofilm based on a mechanical analysis of the biofilm as a viscoelastic fluid. Finally, model results will be compared to experimental data. Experiments will be performed to measure spatio-temporal responses, including both killing and detachment, to antibiotic treatment in a P. aeruginosa experimental system, and these results will be compared with output of the mathematical model. Progress in understanding the stubborn persistence of biofilm infections in the face of antibiotic chemotherapy has been surprisingly slow. This modeling effort will accelerate this effort by integrating the many constituent phenomena that must be considered and serving as a vehicle for dialogue between the diverse disciplines that must communicate to solve this problem. The model will ultimately be a tool for investigating the consequences of hypothesized resistance mechanisms, designing experiments to test these mechanisms, identifying novel treatment strategies, and determining optimal antibiotic dosing protocols. This project will afford a rich interdisciplinary training experience for the three participating graduate students.
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