Revisiting the mode of action of daptomycin considering the inoculum effect and a novel liposome-MIC-competition assay

, not in DAP concentration. The second objective has been to render data on liposomal model systems quantitatively comparable to in vivo data. This is achieved by the liposome-MIC-competition assay combining bacteria and liposomes in a single MIC experiment. It suggests an equivalent phosphatidylglycerol concentration of 3.5E-8 μM/(colony-forming units [CFU]/mL), giving rise to a re-assignment of model studies to comparable in vivo systems. Finally, the data obtained here are combined with common estimates regarding the lipid numbers per bacterium, suggesting that the majority of the bacteria-bound DAP is not localized in the membrane but most likely in the cell wall. Off-target binding is a crucial issue for membrane-active antibiotics.