Ceragenin Mediated Selectivity of Antimicrobial Silver Nanoparticles

Mark A Hoppens , Christopher B Sylvester , Ammar T Qureshi , Thomas Scherr , Desiree R Czapski , Randolph S Duran , Paul B Savage , and Daniel J. Hayes

The understanding that common broad spectrum antimicrobials disrupt natural microbial flora important in acquiring nutrients and preventing infection has resulted in a paradigm shift favoring more selective antimicrobials. This report explores silver nanoparticles conjugated with ceragenin, or cationic antimicrobials (CSA-SNPs), as a potential gram-positive selective antimicrobial. Herein, CSA-SNPs are characterized using TEM, DLS, zeta potential, and HPLC-ESI-TOF-MS. The antimicrobial properties are determined through MIC/MBC and time-kill studies. Spatial selectivity of the conjugate nanoparticle was evaluated using confocal imaging, MATLAB statistical analysis, and video monitored interactions between bacteria and CSA-SNPs via laser trapping techniques. Cytotoxicity is also determined by live/dead staining and flow cytometry. Average particle size as determined through TEM analysis and hydrodynamic diameter determined via DLS are 63.5 +/- 38.8 nm and 102.23 +/- 2.3 nm respectively. The zeta potential of the SNP before and after CSA attachment is -18.23 mV and -8.34 mV. MIC/MBC data suggests CSA-SNPs are eight times more effective against Staphylococcus aureus than SNPs alone. Furthermore, MATLAB analysis of confocal imaging found that 70% of CSA-SNPs are within 2 µm of S. aureus whereas this percentage falls to below 40% with respect to Escherichia coli. These results are bolstered further by laser trapping experiments demonstrating selective adherence of CSA-SNPs conjugates with bacterial strains. Cytotoxicity studies of CSA-SNPs against 3T3 fibroblasts indicate 50% cell viability at 50 ppm.

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