Targeting of Cationic Liposomes to Skin-Associated Bacteria

Cationic vesicles were produced by incorporating positively-charged stearylamine into the lipid bilayers. The addition of stearylamine has been shown to facilitate targeting of liposomes to the skin-associated bacterium Staphylococcus epidermidis. The adsorption of the liposomes to films of the bacteria immobilized on a solid surface has been studied. The extent of adsorption as a function of liposomal lipid concentration could be described in terms of a Langmuir adsorption isotherm, applicable to situations in which species are adsorbed as monolayers on solid surfaces. Analysis on the basis of the Langmuir model enabled the determination of the maximum theoretical targeting to the bacteria and association/dissociation constants for the interaction. The adsorption was examined under conditions of varying ionic strength. Increasing the ionic strength had the effect of decreasing the extent of targeting and suggested that the interaction between the cationic vesicles and sites on the bacterial surface was mediated by electrical double-layer effects. It follows that electrostatic effects make a major contribution to the interaction between these vesicles and S. epidermidis. The attachment of the vesicles is reversible and ionic strength-induced removal of vesicles from the bacteria could be used as a tool to study the delivery of liposomally encapsulated bactericide to the biofilm.