Preventing E. coli biofilm formation with antimicrobial peptide surface coatings: recognizing the dependence on the bacterial binding mode using live-cell microscopy

Antimicrobial peptides (AMPs) can kill bacteria by destabilizing their membranes, yet, to translate these molecules properties into a covalently attached coating is challenging. Standard microbiology methods do not work well for grafted AMPs, particularly it is difficult to distinguish the AMPs bactericidal potency from factors relating to bacterias binding behavior, e.g., which type of and how persistent bacteria-surface contacts that is necessary. Here we present a method combining live-cell microscopy and microfluidics to study the response of E. coli challenged by the same small AMP either in solution or grafted to the surface through click chemistry. The AMP coating initially suppressed bacterial growth as strongly as AMPs in solution. While AMPs in solution eventually killed the E. coli bacteria, those binding to the AMP coating changed contact mode one hour after binding and then became insensitive to it. The transition depended on binding-induced expression of Type 1 fimbriae, which limits contact between the AMPs and the E. coli outer membrane. By quantifying several different factors contributing to the antibacterial efficacy, these measurements provide a holistic understanding of how antibacterial surface coatings function. We therefore expect this tool to be important for the design of elaborate antibacterial coatings that can reduce the need for antibiotics and thus contribute to slower spreading of antibiotic resistance genes.