THE INTERACTION OF CATIONIC LIPOSOMES WITH THE SKIN-ASSOCIATED BACTERIUM STAPHYLOCOCCUS-EPIDERMIDIS - EFFECTS OF IONIC-STRENGTH AND TEMPERATURE

Cationic liposomes have been prepared from dipalmitoylphosphatidylchol ine (DPPC), cholesterol (Chol) and stearylamine (SA). These phospholip id vesicles were exposed to adsorbed biofilms of the skin-associated b acteria Staphylococcus epidermidis, to which they showed a strong affi nity. The interaction (as assessed by the apparent monolayer coverage of the biofilms by liposomes) was described in terms of a Langmuir ads orption isotherm which enabled determination of the maximum theoretica l coverage of the bacterial surface and association/dissociation const ants. The interaction was shown to be dependent on the ionic strength of the surrounding medium; on increasing the ionic strength the biofil m-vesicle dissociation constant decreased. This suggested that the ads orption was mediated by electrostatic effects. The adsorption of the v esicles was examined at various temperatures, enabling determination o f thermodynamic parameters for the interaction. The adsorbed state of the liposomes was energetically favoured and the interaction was entha lpy driven. The Gibbs energies of adsorption were in a range from - 15 to - 19 kJ mol(-1) and the enthalpies of adsorption from - 26 to - 22 kJ mol(-1). Studies using cell populations of different hydrophobicit y showed that the hydrophobic character of the bacterial cells also ha d an effect on the adsorption of the vesicles to the biofilm.