High antimicrobial activity and low human cell cytotoxicity of core-shell magnetic nanoparticles functionalized with an antimicrobial peptide.

Superparamagnetic iron oxide nanoparticles (SPION) functionalized with antimicrobial agents are promising infection-targeted therapeutic platforms when coupled with external magnetic stimuli. These antimicrobial nanoparticles (NPs) may offer advantages in fighting intracellular pathogens as well as biomaterials-associated infections. This requires the development of NPs with high antimicrobial activity without interfering with the biology of mammalian cells. Here, we report the preparation of biocompatible antimicrobial SPION@gold (Au) core-shell NPs based on covalent immobilization of the antimicrobial peptide (AMP) cecropin mellitin (CM) (the conjugate is named AMP-NP). The minimal inhibitory concentration (MIC) of the AMP-NP for Escherichia coli (E. coli) was 0.4 μg/mL, 10-times lower than MIC of soluble CM. The antimicrobial activity of CM depends on the length of spacer between CM and the NP. AMP-NPs are taken up by endothelial (between 60 and 170 pg of NPs per cell) and macrophage (between 18 and 36 pg of NPs per cell) cells and accumulate preferentially in endolysosomes. These NPs have no significant cytotoxic and pro-inflammatory activities for concentrations up to 200 μg/mL (at least 100 times higher than the MIC of soluble CM). Our results in membrane models suggest that the selectivity of AMP-NPs to bacteria and not eukaryotic membranes is due to their membrane compositions. The AMP-NPs developed here open new opportunities for infection-site targeting.