AVS 53rd International Symposium
    Biomaterial Interfaces Tuesday Sessions
       Session BI1-TuM

Paper BI1-TuM1
Getting to the Root of Bacterial Hair

Tuesday, November 14, 2006, 8:00 am, Room 2001

Session: Microbe-Surface Interactions
Presenter: R.J. Emerson, Worcester Polytechnic Institute
Authors: R.J. Emerson, Worcester Polytechnic Institute
T.A. Camesano, Worcester Polytechnic Institute
N.A. Burnham, Worcester Polytechnic Institute
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Many bacteria use their extracellular polymers to attach to surfaces, leading to such phenomena as biofouling and biofilm-initiated infections of medical devices. One method of determining the physicochemical and physicomechanical properties of these hairlike layers is through the acquisition and interpretation of AFM force curves. Most previous researchers have defined the point of zero separation as the cell wall, and assumed the constant compliance region of the force curve to be representative of that location. With the data processed in this manner, the force at the "wall" has been used to calculate the equilibrium length of the brush, as well as the grafting density of the polymers at the point of zero separation. Here, we show: 1) that the constant compliance region frequently occurs in the middle of the layers, 2) how the layer thicknesses may be more accurately quantified, 3) a quantitative method of establishing the position of the "roots of the hairs" at the cell wall, i.e., the true zero of the separation axis, and 4) the more appropriate use of the mesh density of the polymer brush, in lieu of the polymer grafting density. For the specific case of Pseudomonas aeruginosa, a commonly found bacterium in both hospital settings and the natural environment, we have identified two discrete layers, of equilibrium thicknesses 160 ± 8 and 1700 ± 400 nm, with respective mesh densities of (1.9 ± 0.1) x 10@super 26@ m@super -3@ and (7 ± 2) x 10@super 22@ m@super -3@. AFM force curves of bacterial exopolymers can now be meaningfully interpreted.