Polycationic Biocidal Coatings: The Mechanism of Their Interaction with Cells

Application of bacterial cultures to cationic coatings leads to cell dysfunction and death. A traditional "biocidal paradigm" considers cell death resulting from their direct contact with the outer surface of the coating, which carries toxic cationic groups. To clarify the mechanism of antimicrobial polymer action, model anionic polymer microspheres, fixed K562 cells, and Gram-negative bacteria Pseudomonas aeruginosa and Gram-positive bacteria Staphylococcus aureus have been deposited over the coatings from synthetic cationic poly(diallyldimethylammonium chloride). The cells come from the environment in small water-salt droplets, which adsorb on the coating and induce a set of processes, including (1) dissolution of the polycation and its binding to the cells, (2) migration of the polycation between individual cells in solution, (3) adsorption of polycation-cell complex onto the coating, and (4) transfer of the polycation from the coating to the cell surface. Taking together, these processes ensure high efficacy of the biocidal action of cationic polymer coatings. The fact that cells are washed off the coatings being bound to cationic polymer should be taken into account when designing antimicrobial experiments and interpreting results.