Polyhydroxy-mediated interactions between liposomes and bacterial biofilms

A theoretical model has been developed for the interaction of the surface polymers of the bacterial glycocalyx with liposomes incorporating lipids with polyhydroxy headgroups such as phosphatidylinositol (PI). The theory is based on a lattice model and equations are derived for the potential energy of interaction between the surfaces of a bacterium and a liposome as a function of their separation. It is shown that a relatively small energy of interaction, less than that of a single hydrogen bond, between the polyhydroxyl headgroup of the liposomal lipid and bacterium surface polymer residues could give rise to a potential energy of interaction in excess of the classical double layer repulsive force and attractive dispersion force interactions. The most important prediction of the theory is that the potential energy of interaction goes through a minimum as a function of the polyhydroxy lipid (PI) concentration in the liposomal surface, thus predicting an optimal liposomal composition for adsorption of liposome to bacterium. This result is in concordance with the adsorption of dipalmitoylphosphatidylcholine-PI liposomes to a range of biofilms of oral and skin-associated bacteria on solid supports, where optimum levels of PI for adsorption have been found. The theory demonstrates that subtle changes in the composition of liposomal and bacterial surfaces involving relatively small interaction energies can markedly influence the nature of their interactions.