Effect of lipid composition on activity of liposome-entrapped ampicillin against intracellular Listeria monocytogenes

The effect of lipid composition on the intracellular antibacterial activity of ampicillin-containing liposomes was studied in vitro by using mouse peritoneal macrophages infected with Listeria monocytogenes. Two types of liposomes, a fluid type, consisting of cholesterol-phosphatidylcholine-phosphatidylserine (5:4:1), and a solid type, consisting of cholesterol-distearoylphosphatidylcholine-dipalmitoylphosphatidylglyc ero l (10:10:1), were used. Although the cellular uptake of both types of liposomes was similar, they differed with respect to the rate of intracellular degradation. A correlation was found between the relatively slow degradation of the solid liposomes and a delayed intracellular release of the encapsulated ampicillin, as reflected in absent or delayed intracellular killing of L. monocytogenes.