(542f) Salt Effects on Synthetic Cationic Antimicrobial Polymer-Cell Interactions

Synthetic polycations are widely studied antiseptics, but their mechanisms of action are not fully understood. Better understandings of their mechanisms and interactions are needed to design better antimicrobial polymer formulations. As polycation-cell interactions are partially governed by electrostatics, and salts are commonly found in biological systems where antiseptics would be deployed, the effect of salt on polycation-cell interactions warrants further study.

Polymer adsorption onto cells were studied with a fluorescently tagged polyelectrolyte, polydiallyldimethyl ammonium chloride (PDADMAC). Adsorption of the polymer onto bacterial cells (E. coli, S. aureus, and P. aeruginosa) was observed in a parallel-plate flow chamber via fluorescence microscopy. The polymer was flowed over cells adhered to the flow chamber window along with SYTOX blue, a stain indicating cell permeabilization, which is often correlated with cell death. Time-lapse video was analyzed to measure the adsorption of PDADMAC and the permeability for each cell.

Both PDADMAC antimicrobial activity and adsorption decreased with increasing NaCl concentration, as well as adsorption capacity. Above 0.15 M NaCl, PDADMAC adsorbed, but did not kill the cells but it did prevent further growth, essentially acting as a bacteriostat. When PDADMAC was washed from the cell surface, the cells resumed growth, showing that the bacteriostatic effect is reversible under certain conditions. When PDADAMAC coverage on the cell was too high, cells undergo a morphological change where they shrink, and cannot regrow even when PDADMAC is removed. These morphological changes are absent when the NaCl concentration is high.