Project description:Understanding how pathogens respond to antimicrobial peptides, and how this compares to currently available antibiotics, is crucial to optimizing antibiotic therapy. Staphylococcus aureus has several known resistance mechanisms against human cationic antimicrobial peptides (CAMPs). We aim to determine how S. aureus responds to sheep and frog CAMPs, and whether this response is associated with resistance. Gene expression changes in Staphylococcus aureus Newman cells exposed to linear CAMPs were analyzed by DNA microarray. Three antimicrobial peptides were used in the analysis, two of them are derived from frog, temporin L and dermaseptin K4-S4(1-16), one is from sheep, ovispirin-1. The peptides induced the VraSR cell-wall regulon and several other genes which are also upregulated in cells treated with vancomycin and other cell wall-active antibiotics. In addition to this similarity, three genes/operons were particularly strongly induced by the peptides: vraDE, SA0205 and SAS016, encoding an ABC transporter, a putative membrane-bound lysostaphin-like peptidase and a small functionally unknown protein, respectively. Ovispirin-1 and dermaseptin K4-S4(1-16), which disrupt lipid bilayers by the carpet mechanism, were strong inducers of the vraDE operon. We show that high level induction by ovispirin-1 was dependent on the amide modification of the peptide C-terminus. This suggests that the amide group has a crucial role in the activation of the Aps sensory system, the regulator of vraDE. In contrast, temporin L, which disrupts lipid bilayers by forming pores, was clearly a weaker inducer of vraDE despite the C-terminal amide modification. Sensitivity testing with CAMPs and other antimicrobials suggested that VraDE is a transporter dedicated to resist bacitracin. We also showed that SA0205 belongs to the VraSR regulon. Furthermore, VraSR was shown to be important for resistance against a wide range of cell wall-active antibiotics and other antimicrobial agents including the amide-modified ovispirin-1, bacitracin, teicoplanin, cefotaxime and 10 other β-lactam antibiotics, chlorpromazine, thioridazine and EGTA.

Project description:The search for next-generation antibacterial compounds that overcome the development of resistance can be facilitated by identifying how to target the cell membrane of bacteria. Understanding the key molecular features that enable interactions with lipids and lead to membrane disruption is therefore crucial. Here, we employ a library of lipid-like compounds (lipidoids) comprising modular structures with tunable hydrophobic and hydrophilic architecture to shed light on how the chemical functionality and molecular shape of synthetic amphiphilic compounds determine their activity against bacterial membranes. Synthesized from combinations of 8 different polyamines as headgroups and 13 acrylates as tails, 104 different lipidoids are tested for activity against a model Gram-positive bacterial strain (Bacillus subtilis). Results from the combinatorial screening assay show that lipidoids with the most potent antimicrobial properties (down to 2 μM) have intermediate tail hydrophobicity (i.e., c log P values between 3 and 4) and lower headgroup charge density (i.e., longer spacers between charged amines). However, the most important factor appeared to be the ability of a lipidoid to self-assemble into an inverse hexagonal liquid crystalline phase, as observed by small-angle X-ray scattering (SAXS) analysis. The lipidoids active at lowest concentrations, which induced the most significant membrane damage during propidium iodide (PI) permeabilization assays, were those that aggregated into highly curved inverse hexagonal liquid crystal phases. These observations suggest that the introduction of strong curvature stress into the membrane is one way to maximize membrane disruption and lipidoid antimicrobial activity. Lipidoids that demonstrated the ability to furnish this phase consisted of either (i) branched or linear headgroups with shorter linear tails or (ii) cyclic headgroups with 4 bulky nonlinear tails. On the contrary, lipidoids previously observed to adopt disc-like conformations that pack into bicontinuous cubic phases were significantly less effective against B. subtilis. The discovery of these structure-property relationships demonstrates that it is not simply a balance of hydrophobic and hydrophilic moieties that govern membrane-active antibacterial activity, but also their intrinsic curvature and collective behavior.

Project description:Understanding how pathogens respond to antimicrobial peptides, and how this compares to currently available antibiotics, is crucial to optimizing antibiotic therapy. Staphylococcus aureus has several known resistance mechanisms against human cationic antimicrobial peptides (CAMPs). We aim to determine how S. aureus responds to sheep and frog CAMPs, and whether this response is associated with resistance. Gene expression changes in Staphylococcus aureus Newman cells exposed to linear CAMPs were analyzed by DNA microarray. Three antimicrobial peptides were used in the analysis, two of them are derived from frog, temporin L and dermaseptin K4-S4(1-16), one is from sheep, ovispirin-1. The peptides induced the VraSR cell-wall regulon and several other genes which are also upregulated in cells treated with vancomycin and other cell wall-active antibiotics. In addition to this similarity, three genes/operons were particularly strongly induced by the peptides: vraDE, SA0205 and SAS016, encoding an ABC transporter, a putative membrane-bound lysostaphin-like peptidase and a small functionally unknown protein, respectively. Ovispirin-1 and dermaseptin K4-S4(1-16), which disrupt lipid bilayers by the carpet mechanism, were strong inducers of the vraDE operon. We show that high level induction by ovispirin-1 was dependent on the amide modification of the peptide C-terminus. This suggests that the amide group has a crucial role in the activation of the Aps sensory system, the regulator of vraDE. In contrast, temporin L, which disrupts lipid bilayers by forming pores, was clearly a weaker inducer of vraDE despite the C-terminal amide modification. Sensitivity testing with CAMPs and other antimicrobials suggested that VraDE is a transporter dedicated to resist bacitracin. We also showed that SA0205 belongs to the VraSR regulon. Furthermore, VraSR was shown to be important for resistance against a wide range of cell wall-active antibiotics and other antimicrobial agents including the amide-modified ovispirin-1, bacitracin, teicoplanin, cefotaxime and 10 other β-lactam antibiotics, chlorpromazine, thioridazine and EGTA. The effects of the three different antimicrobial peptides on gene expression of S. aureus Newman were studied by using whole genome oligo-DNA microarrays. Bacteria were grown in BHI medium to the early exponential phase (OD600=0.6) and antimicrobial peptides were added at sublethal concentrations. Samples were taken for RNA isolations after treating the cultures with the peptides for 10 minutes. Control cultures without peptide additions were treated similarly and in parallel.

Dataset Information

Effect of ring size on conformation and biological activity of cyclic cationic antimicrobial peptides.

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Effect of ring size on conformation and biological activity of cyclic cationic antimicrobial peptides.

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