AFM experimental set-up and the resulting force-distance curve.

<p><b>A</b>. Schematic presentation of the experimental AFM set-up depicting lactobacilli immobilized on poly-L-Lysine coated glass and a staphylococcus attached to the AFM cantilever. <b>B</b>. Fluorescence image of a bacterial probe coated with <i>S. aureus</i> Newman. The tipless cantilever (Bruker; Camarillo, CA) was prepared according to the methods outlined in the paper, used for AFM force adhesion experiments and stained using LIVE/DEAD <i>Bac</i>light viability stain (Molecular Probes Europe BV; Leiden, The Netherlands). Green spots represent viable bacteria. <b>C</b>. Schematic presentation of the cantilever deflection and the resulting force-distance curve upon approach and retraction of two bacteria in AFM. At large separation distances, no adhesion force is measured between bacteria (1), while at closer approach, repulsion occurs between the interacting bacteria, indicated by positive force values (2). Upon retraction, an attractive, negative force is measured (3).