Amphiphilic quaternary ammonium chitosans self-assemble onto bacterial and fungal biofilms and kill adherent microorganisms.

Formation of biofilms on solid surfaces is a long-standing challenge to multiple medical and health-related applications. Once formed, biofilms are very difficult to destroy, and microorganisms in biofilms are much more resistant to antimicrobial agents than their free-floating counterparts. The current antimicrobial agents/disinfectants often have low residence time on biofilms, leading to low antimicrobial effect on biofilm microorganisms. We designed and synthesized an amphiphilic quaternary ammonium chitosan (CS612) as biocompatible antimicrobial agents that bind onto preformed biofilms to kill adherent microorganisms. CS612 was synthesized through an external acid-free approach, and showed excellent concentration-dependent cytocompatibility toward mammalian cells. Antimicrobial functions of CS612 were confirmed by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests against Gram-positive bacteria, Gram-negative bacteria, and fungi. CS612 rapidly bound onto preformed bacterial and fungal biofilms, and killed adherent microorganisms living in the biofilms. The biofilm-binding kinetic parameters were determined, pointing to a new strategy to manage microorganisms in biofilms and their accompanying problems.