FIGURE 5.

Force-distance curves showing the interactions of the AFM tip with the bacterial surfaces. (a) L. johnsonii DSM20533; (b) L. johnsonii ATCC332; (c) L. johnsonii ATCC33200; (d) L. crispatus DSM20584; (e) L. helveticus ATCC12046; and (f) L. helveticus ATCC15009. The microorganisms are adhered to a poly-L-lysine covered substrate. The force-distance curves are obtained in a 10 mM KH₂PO₄ buffer at pH 7. The L. johnsonii strains (a–c) show clear adhesion peaks upon retraction of the AFM tip from the bacterial surface. The adhesion curves of L. johnsonii DSM20533 and L. johnsonii ATCC332 show multiple unbinding events upon retraction, whereas for L. johnsonii ATCC33200 the unbinding appears to proceed via a single event. For the L. crispatus DSM20584, no significant adhesion between the bacterial surface and the AFM tip is observed upon retraction; adhesion events are also rarely recorded for the two L. helveticus strains. From the force-distance curves, elasticity data are calculated (Table 4).