Effect of composition on the in vitro activity of fusogenic liposomes loaded with vancomycin against gram-negative bacteria.

In a previous note, small unilamellar liposomes were prepared using an extrusion procedure (SUVETs) from a lipid mixture known for its fusogenic properties towards eukaryotic cell membranes (namely, dipalmitoylphosphatidylcholine, DPPC; dioleoylphosphatidylethanolamine, DOPE; and cholesterol hemisuccinate, CHEMS). The antibiotic vancomycin (VAN) was loaded with high efficiency in these vesicles that, in vitro, were able to inhibit the growth of wild and standard Gram-negative bacterial strains. Since neither the free antibiotic nor VAN-loaded ‘classical’ (non fusogenic) liposomes showed any activity against the same microorganisms, we have further developed the investigation by preparing a series of VAN-loaded fusogenic SUVETs, in which the molar ratios between the three ingredients was varied, or alternatively removing one of them.In this paper we present the technological details and the in vitro microbiological data of these new SUVETs. All the prepared samples showed a close profile of activity against the tested bacterial strains. This confirms that the activity of liposomal VAN against Gram-negative bacteria appears to be linked both to the presence of the fusogenic DOPE and the inclusion of CHEMS in the composition of the liposomes.