Antimicrobial coatings from gramicidin D nanoparticles and polymers

Abstract

The microbicidal activity of gramicidin D molecules (Gr) assembled as nanoparticles (NPs) against Staphylococcus aureus was found to be superior to that of other Gr formulations in bilayers. In combination with the antimicrobial polymer poly(diallyl dimethyl ammonium chloride) (PDDA), water dispersions and coatings on glass exhibited a remarkably broadened spectrum of activity, achieving complete killing of Gram-negative bacteria, Gram-positive bacteria and fungi at reduced Gr and PDDA doses. In this work, combinations of Gr NPs and polymers were cast on glass (hydrophilic) or polyethylene (hydrophobic) surfaces, modeling common surfaces on biomedical materials, to evaluate the effect of polymer positive charge on the antimicrobial activity. Decreasing positive charges of three different polymers, namely PDDA, chitosan (CH) and polyacrylamide (PA), reduced or abolished microbicidal activity both in the presence and absence of Gr NPs. At 4.7 μg Gr and 25 μg polymer, microbicidal activity increased from PA to CH to PDDA at pH 6.3. The results suggested that the Gr/polymer antimicrobial coatings can be used on both hydrophobic and hydrophilic biomedical materials, effectively imparting them with efficient defense against a broad spectrum of microbes.