Preventing E. coli Biofilm Formation with Antimicrobial Peptide-Functionalized 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 translating these molecules' properties into a covalently attached antibacterial coating is challenging. Rational design efforts are obstructed by the fact that standard microbiology methods are ill-designed for the evaluation of coatings, disclosing few details about why grafted AMPs function or do not function. It is particularly difficult to distinguish the influence of the AMP's molecular structure from other factors controlling the total exposure, including which type of bonds are formed between bacteria and the coating and how persistent these contacts are. Here, we combine label-free live-cell microscopy, microfluidics, and automated image analysis to study the response of surface-bound Escherichia coli challenged by the same small AMP either in solution or grafted to the surface through click chemistry. Initially after binding, the grafted AMPs inhibited bacterial growth more efficiently than did AMPs in solution. Yet, after 1 h, E. coli on the coated surfaces increased their expression of type-1 fimbriae, leading to a change in their binding mode, which diminished the coating's impact. The wealth of information obtained from continuously monitoring the growth, shape, and movements of single bacterial cells allowed us to elucidate and quantify the different factors determining the antibacterial efficacy of the grafted AMPs. We expect this approach to aid the design of elaborate antibacterial material coatings working by specific and selective actions, not limited to contact-killing. This technology is needed to support health care and food production in the postantibiotic era.

Lateral membrane organization as target of an antimicrobial peptidomimetic compound

Antimicrobial resistance is one of the leading concerns in medical care. Here we study the mechanism of action of an antimicrobial cationic tripeptide, AMC-109, by combining high speed-atomic force microscopy, molecular dynamics, fluorescence assays, and lipidomic analysis. We show that AMC-109 activity on negatively charged membranes derived from Staphylococcus aureus consists of two crucial steps. First, AMC-109 self-assembles into stable aggregates consisting of a hydrophobic core and a cationic surface, with specificity for negatively charged membranes. Second, upon incorporation into the membrane, individual peptides insert into the outer monolayer, affecting lateral membrane organization and dissolving membrane nanodomains, without forming pores. We propose that membrane domain dissolution triggered by AMC-109 may affect crucial functions such as protein sorting and cell wall synthesis. Our results indicate that the AMC-109 mode of action resembles that of the disinfectant benzalkonium chloride (BAK), but with enhanced selectivity for bacterial membranes.

Selective Intracellular Delivery of Thiolated Cargo to Tumor and Neovasculature Cells Using Histidine-Rich Peptides as Vectors

Short histidine-rich peptides could serve as novel activatable vectors for delivering cytotoxic payloads to tumor and neovasculature cells. This explorative study reports preliminary results showing that zinc ions, which are found in elevated levels at neovasculature sites, can trigger the intracellular delivery of a short antimicrobial peptide when conjugated to a histidine-rich peptide through a disulfide bond. The importance of exofacial thiols in the mode of action of these disulfide-linked conjugates is also shown.

The Medicinal Chemistry of Short Lactoferricin-Based Antibacterial Peptides

This review discusses antibacterial peptides from the perspective of development into clinically useful chemotherapeutic drugs using short lactoferricin based peptides as examples. The review shows how important features for antibacterial activity can be identified and explored using the molecular properties of a range of natural and non-natural amino acids. The results have been further refined quantitatively using a "soft-modelling" approach where important structural parameters that influence the antibacterial activity of 15-residue model peptides were identified. The review describes how this knowledge is utilised to generate pharmacophores for antibacterial efficacy. These pharmacophores turn out to be surprisingly small and relatively consistent between typical Gram-negative and Gram-positive bacteria leading to the discovery of a novel class of short synthetic cationic antimicrobial peptides. These compounds are found to have high antibacterial activity against several bacterial strains that are resistant to commercial antibiotics, and are promising as future clinical candidates for treatment of infections caused by several clinically relevant pathogens.