The adsorption of cationic liposomes to Staphylococcus aureus biofilms

Cationic liposomes were prepared by extrusion (VETs) from mixtures of dipal mitoylphosphatidylcholine (DPPC), cholesterol and the cationic lipids stear ylamine (SA), dimethyldioctadecylammonium bromide (DDAB) and dimethylaminoe thane carbamoyl cholesterol (DC-chol) covering ranges of cationic lipid mol %. The liposomes were approximately 120 nm diameter. The adsorption of the liposomes to biofilms of the bacterium Staphylococcus aureus was measured a s a function of liposome composition and liposomal lipid concentration. Ads orption as a function of liposomal lipid concentration could be fitted by t he Langmuir equation, which was used to obtain the association constants an d limiting adsorption values. For liposomes of composition DPPC-cholesterol -SA adsorption passed through a maximum as a function of mole percent SA. Z eta potential measurements were used to show that the maximum arose possibl y as a consequence of the loss of SA from liposomes with a high SA content and its adsorption onto the bacteria, which reduced their affinity for inta ct cationic liposomes. The permeability coefficient of DPPC-cholesterol-DDA B liposomes to the antibiotic vancomycin was determined and liposomes incor porating the vancomycin were shown to inhibit bacterial growth from biofilm s and were more effective than an equivalent amount of free vancomycin for short (up to 30 min) liposome-biofilm incubation times. (C) 1999 Elsevier S cience B.V. All rights reserved.