Capture of Capsular Bacteria from Flow via Polymer Depletion

Because bacterial adhesion on surfaces is the first step of infection and biofilm formation, surfaces have been developed to prevent cell adhesion. We demonstrate here that E cells can be immobilized on otherwise non-adhesive surfaces through the introduction of a non-adsorbing polyethylene oxide polymer. The depletion-driven cell capture can occur in gentle shear flow and is reversible. The free polymer additionally causes reversible aggregation of cells in free solution; however, cell concentrations are below those typically associated with depletion-driven fluid-solid phase transitions. Because cell aggregates experience stronger shearing forces than do individual cells, adhesion of individual cells is preferred over that of aggregates. While cells captured on physico-chemically adhesive surfaces tend to adsorb by their ends in a variety of tipped configurations relative to the surface, depletion-driven cell capture brings cells more nearly flat to the surface. The aggregated and captured cells are living and are observed to grow into microcolonies.