Nanoclay-induced bacterial flocculation for infection confinement

Effects of size and charge of anionic nanoclays on their interactions with bacteria-mimicking lipid membranes, bacterial lipopolysaccharide (LPS), and Gram-negative bacteria were investigated using ellipsometry, dynamic light scattering, ζ-potential measurements, and confocal microscopy combined with Live/Dead staining. Based on particle size and charge density, three different anionic hectorite nanoclays were employed, and investigated in the presence and absence of the net cationic human antimicrobial peptide LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES). In the absence of this peptide, the nanoclays were found not to bind to similarly anionic bacteria-mimicking model phospholipid membranes, nor to destabilize these. Similarly, while all nanoclays induced aggregation of Escherichia coli bacteria, the flocculated bacteria remained alive after aggregation. In contrast, LL-37 alone, i.e. in the absence of nanoclay particles, displays antimicrobial properties through membrane lysis, but does not cause bacterial aggregation in the concentration range investigated. After loading the nanoclays with LL-37, potent bacterial aggregation combined with bacterial membrane lysis was observed for all nanoclay sizes and charge densities. Demonstrating the potential of these combined systems for confinement of infection, LPS-induced NF-κB activation in human monocytes was found to be strongly suppressed after nanoclay-mediated aggregation, with a wide tolerance for nanoparticle size and charge density.