Reversibility of bacterial adhesion at an electrode surface

Deposition of four bacterial strains from a 1 mM potassium phosphate buffer (pH 7) to an indium tin oxide (ITO) electrode surface has been studied in a parallel plate flow chamber at three electrode potentials (-0.2, 0.1, and 0.5 V). Capacitance measurements demonstrated that the ITO surface was neg atively charged with respect to the solution at the electric potentials app lied, that is, bacteria deposited under repulsive electrostatic conditions. Initial deposition rates were independent of the electrode potential, exce pt for Actinomyces naeslundii T14V-J1. Application of a more negative elect rode potential yielded increased desorption of Streptococcus oralis J22, St aphylococcus epidermidis 3399, and A. naeslundii 147, whereas for A. naeslu ndii T14V-J1 desorption decreased. If a high (greater than or equal to 65 m uA) cathodic current was applied by adjusting the potential between -0.4 an d -0.5 V, adhering bacteria were stimulated to desorb with desorption proba bilities increasing with increasing current density. Bacterial desorption c ould be described on the basis of the Derjaguin-Landau-Verwey-Overbeek theo ry assuming secondary minimum adhesion, except for A. naeslundii T14V-J1. W hen bacteria were forced to adhere in the primary minimum by application of a high (1.8 V) positive electrode potential during deposition, adhering ba cteria could hardly be stimulated to desorb, indicating strong, irreversibl e adhesion. The deviating behavior of A. naeslundii T14V-J1 was attributed to direct contact between its relatively long surface appendages and the el ectrode surface.