Miltefosine impacts small molecule transport in Gram-positive bacteria

Miltefosine (MLT) is an alkylphosphocholine with clinical success as an anticancer and antiparasitic drug. Although the mechanism of action of MLT is highly debated, the interaction of MLT with the membrane, specifically lipid rafts of eukaryotes, is well-documented. Recent reports suggest MLT impacts the functional membrane microdomains in bacteria - regions of the membrane structurally and functionally similar to lipid rafts. There have been conflicting reports, however, as to whether MLT impacts the overall fluidity of cellular plasma membranes. Here, we apply steady-state fluorescence techniques, generalized polarization of laurdan and anisotropy of diphenylhexatriene, to discern how MLT impacts the global ordering and lipid packing of Staphylococcus aureus membranes. Additionally, we investigate how the transport of a range of small molecules is impacted by MLT for S. aureus and Bacillus subtilis by employing time-resolved second harmonic scattering. Overall, we observe MLT does not have an influence on the overall ordering and packing of S. aureus membranes. Additionally, we show that the transport of small molecules across the membrane can be significantly altered by MLT - although this is not the case for all molecules studied. The results presented here illustrate the potential use of MLT as an adjuvant to assist in the delivery of drug molecules in bacteria.