Antimicrobial Activity of Peptidomimetics against Multidrug-Resistant Escherichia coli: A Comparative Study of Different Backbones

Novel remedies in the battle against multidrug-resistant bacterial strains are urgently needed, and one obvious approach involves antimicrobial peptides and mimics hereof. The impact of α- and β-peptoid as well as β³-amino acid modifications on the activity profile against β-lactamase-producing Escherichia coli was assessed by testing an array comprising different types of cationic peptidomimetics obtained by a general monomer-based solid-phase synthesis protocol. Most of the peptidomimetics possessed high to moderate activity toward multidrug-resistant E. coli as opposed to the corresponding inactive peptides. Nevertheless, differences in hemolytic activities indicate that a careful choice of backbone design constitutes a significant parameter in the search for effective cationic antimicrobial peptidomimetics targeting specific bacteria

MIC (µg/mL) for wild-type <i>E. coli</i> and four peptidomimetic-adapted isolates against peptidomimetic 1 in standard MHB media and in MHB media supplemented with 25% human blood plasma.

a<p>Ability of plasma to interact synergistically with peptidomimetic 1.</p

Structure of the peptidomimetics used in this study.

<p>The structure of peptidomimetic 1 used for continuous culturing of <i>Escherichia coli</i> and the structure of peptidomimetics 2 and 3 to which cross-resistance was demonstrated.</p

Minimum Inhibitory Concentration (µg/mL) of the adapted <i>E. coli</i> lineages against peptidomimetic 1 immediately after peptidomimetic adaptation and after 35 generations with no peptidomimetic.

a<p>MIC values are based on two technical duplicates.</p>b<p>Not determined due to lack of growth of revived freezing stocks in supplemented media.</p>c<p><i>E. coli</i> ATCC 25922 had a wt MIC of 8 µg/mL.</p

Grouping of genome-sequenced peptidomimetic-adapted isolates based on comparison to wild type (wt) MIC value (8 µg/mL).

<p>Grouping of genome-sequenced peptidomimetic-adapted isolates based on comparison to wild type (wt) MIC value (8 µg/mL).</p

Heterogeneity in lineage populations.

<p>Minimum Inhibitory Concentration (MIC) for peptidomimetic 1 against population isolates of lineage no. 2 (A), lineage no. 4 (B), lineage no. 5 (C) and lineage no. 7 (D). Bars indicate biological replicates; MIC for all isolates was determined twice, a third replicate was performed for isolates 2–3 and 2–8 due to large variations in results. Susceptibility to peptidomimetic 1 varies widely within the populations. Solid line: population MIC; punctuated line: wt MIC (8 µg/mL).</p

Cross-resistance between peptidomimetic 1 and 2.

<p>Association between Minimum Inhibitory Concentration (MIC) for peptidomimetic 1 and peptidomimetic 2 against lineage no. 2 (black circles) and lineage no. 5 (white circles). <i>E. coli</i> ATCC 25922 MIC is highlighted with an asterisk (i.e. MIC values of 8 µg/mL and 64 µg/mL for peptidomimetic 1 and 2, respectively). This data point is shared with six of the ten isolates from lineage no. 5. Also, for lineage 2 three isolates (2–7, 2–9 and 2–10) shared the same MIC values (peptidomimetic 1∶256 µg/mL, peptidomimetic 2∶512 µg/mL) as did the two isolates 2–4 and 2–6 (peptidomimetic 1∶96 µg/mL, peptidomimetic 2∶512 µg/mL). All values are based on two biological replicates; the mean value is displayed when results varied.</p

Minimum Inhibitory Concentration (µg/mL) of the adapted <i>E. coli</i> lineages against polymyxin immediately after polymyxin adaptation and after 35 generations with no polymyxin.

a<p>MIC values are based on two technical duplicates.</p>b<p>Not determined since lineage was unable to grow at 32×wt MIC.</p>c<p><i>E. coli</i> ATCC 25922 had a wt MIC of 1 µg/mL.</p

Distribution of single-nucleotide polymorphisms (SNPs) and deletion-insertion polymorphism (DIPs) that caused an amino acid change and had a frequency above 80% in the peptidomimetic-adapted genome-sequenced isolates.

a1<p>isolates with high levels of resistance i.e. 8–16×wild type MIC, ² isolates with intermediate levels of resistance i.e. 4–8×wt MIC; ³ Isolates with wild type MIC.</p>b<p>Two SNPs were present in the <i>macB</i> gene: one SNP causing amino acid 319 in the protein to change from Asp to Tyr (X) and one causing amino acid 505 to change from Trp to Leu (x).</p>c<p>Two SNPs were present in the <i>macA</i> gene: one SNPs causing amino acid 91 in the protein to change from Val to Gly (X) and one causing amino acid 205 to change from Val to Leu (x).</p>d<p>DIP mutations; all other mutations are SNPs.</p

Lipidated α‑Peptide/β-Peptoid Hybrids with Potent Anti-inflammatory Activity

In this study, we investigated, optimized, and characterized a novel subclass of host defense peptide (HDP) mimics based on α-peptide/β-peptoid hybrid oligomers with an alternating cationic/hydrophobic design with respect to their ability to modulate the pro-inflammatory response by human primary leukocytes upon exposure to bacterial components. Structure–activity studies revealed that certain lipidated α-peptide/β-peptoid hybrid oligomers possess anti-inflammatory activities in the submicromolar range with low cytotoxicity, and that the anti-inflammatory activity of the HDP mimics is dependent on the length and position of the lipid element(s). The resulting lead compound, Pam-(Lys-βNSpe)₆-NH₂, blocks LPS-induced cytokine secretion with a potency comparable to that of polymyxin B. The mode of action of this HDP mimic appears not to involve direct LPS interaction since it, in contrast to polymyxin B, displayed only minor activity in the <i>Limulus</i> amebocyte lysate assay. Flow cytometry data showed specific interaction of a fluorophore-labeled lipidated α-peptide/β-peptoid hybrid with monocytes and granulocytes indicating a cellular target expressed by these leukocyte subsets