Nutritional cues differentially influence the activities of the three quorum sensing (QS) circuits—Las, Rhl, and Pqs—in the pathogen Pseudomonas aeruginosa. A full understanding of how these systems ...work together to tune virulence factor production to the environment is lacking. Here, we used chemical probes to evaluate the contribution of each QS circuit to virulence in wild-type P. aeruginosa under defined environmental conditions. Our results indicate that Rhl and Pqs drive virulence factor production in phosphate- and iron-limiting environments, while Las has a minor influence. Consequently, simultaneous inhibition of Rhl and Pqs can attenuate virulence in environments where Las inhibition fails. The activity trends generated in this study can be extrapolated to predict QS inhibitor activity in infection-relevant environments, such as cystic fibrosis sputum. These results indicate that environmental signals can drastically alter the efficacy of small-molecule QS inhibitors in P. aeruginosa and possibly other pathogens.
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•The Rhl and Pqs QS systems tune virulence factor production to the environment•Small-molecule QS inhibitors have environment-dependent activity•Cocktails of QS inhibitors can best attenuate virulence factor production•Inhibitor cocktails are active in environments that mimic infection (CF sputum)
Welsh and Blackwell show that small-molecule quorum sensing (QS) inhibitors have environment-dependent activity and that cocktails of QS inhibitors can attenuate virulence factor production under conditions where targeting a single QS circuit is ineffective.
Oligomers of N-substituted glycine, or peptoids, are versatile tools to probe biological processes and hold promise as therapeutic agents. An underlying theme in the majority of recent peptoid ...research is the connection between peptoid function and peptoid structure. For certain applications, well-folded peptoids are essential for activity, while unstructured peptoids appear to suffice, or even are superior, for other applications. Currently, these structure-function connections are largely made after the design, synthesis, and characterization process. However, as guidelines for peptoid folding are elucidated and the known biological activities are expanded, we anticipate these connections will provide a pathway toward the de novo design of functional peptoids. In this perspective, we review several of the peptoid structure-function relationships that have been delineated over the past five years.
Bacterial biofilms are exceptionally difficult to clear using traditional antibiotics and constitute a significant health threat. 2‐Aminobenzimidazole derivatives (see scheme) are capable of strongly ...inhibiting the growth of and dispersing Pseudomonas aeruginosa biofilms. These molecules were found to modulate quorum sensing in reporter strains, and represent some of strongest P. aeruginosa biofilm inhibitors known.
The opportunistic pathogen Pseudomonas aeruginosa uses three interwoven quorum-sensing (QS) circuitsLas, Rhl, and Pqsto regulate the global expression of myriad virulence-associated genes. ...Interception of these signaling networks with small molecules represents an emerging strategy for the development of anti-infective agents against this bacterium. In the current study, we applied a chemical approach to investigate how the Las-Rhl-Pqs QS hierarchy coordinates key virulence phenotypes in wild-type P. aeruginosa. We screened a focused library of synthetic, non-native N-acyl l-homoserine lactones and identified compounds that can drastically alter production of two important virulence factors: pyocyanin and rhamnolipid. We demonstrate that these molecules act by targeting RhlR in P. aeruginosa, a QS receptor that has seen far less scrutiny to date relative to other circuitry. Unexpectedly, modulation of RhlR activity by a single compound induces inverse regulation of pyocyanin and rhamnolipid, a result that was not predicted using genetic approaches to interrogate QS in P. aeruginosa. Further, we show that certain RhlR agonists strongly repress Pqs signaling, revealing disruption of Rhl-Pqs cross-regulation as a novel mechanism for QS inhibition. These compounds significantly expand the known repertoire of chemical probes available to study RhlR in P. aeruginosa. Moreover, our results suggest that designing chemical agents to disrupt Rhl-Pqs crosstalk could be an effective antivirulence strategy to fight this common pathogen.
uses small peptides to assess its population densisty (
, quorum sensing) and regulate virulence at high cell number. Here, we report the design and synthesis of peptidomimetics based on these native ...signals that strongly block this communication pathway in all four specificity groups of
.
The growing threat of antibiotic resistance necessitates the development of novel antimicrobial therapies. Antivirulence agents that target group-beneficial traits in microorganisms (i.e., phenotypes ...that help the cells surrounding the producer cell instead of selfishly benefiting only the producer cell) represent a new antimicrobial approach that may be robust against the spread of resistant mutants. One prominent group-beneficial antivirulence target in bacteria is quorum sensing (QS). While scientists are producing new QS inhibitors (QSIs) at an increasing pace for use as research tools and potential therapeutic leads, substantial work remains in empirically demonstrating a robustness against resistance. Herein we report the results of in vitro competition studies in Pseudomonas aeruginosa that explicitly confirm that two separate barriers can impede the spread of resistance to QSIs: (1) insufficient native QS signal levels prevent rare QSI-resistant bacteria from expressing their QS regulon, and (2) group-beneficial QS-regulated phenotypes produced by resistant bacteria are susceptible to cheating by QSI-sensitive neighbors, even when grown on a solid substrate with limited mixing to mimic infected tissue. These results underscore the promise of QSIs and other antivirulence molecules that target group beneficial traits as resistance-robust antimicrobial treatments and provide support for their further development.
Many types of slippery liquid‐infused porous surfaces (‘SLIPS’) can resist adhesion and colonization by microorganisms. These ‘slippery’ materials thus offer approaches to prevent fouling on ...commercial and industrial surfaces. However, while SLIPS can prevent fouling on surfaces to which they are applied, they can currently do little to prevent the proliferation of non‐adherent organisms. Here, multi‐functional SLIPS are reported that address this issue and expand the potential utility of these materials. The approach is based on the release of antimicrobial agents from the porous matrices used to host the infused oil phases. It is demonstrated that SLIPS fabricated from nanoporous polymer multilayers can prevent colonization and biofilm formation by four common fungal and bacterial pathogens, and that the polymer and oil phases comprising these materials can be used to sustain the release of triclosan, a model antimicrobial agent, into surrounding media. This approach improves the inherent anti‐fouling properties of these materials and endows them with the ability to kill non‐adherent pathogens. This strategy has the potential to be general; the strategies and concepts reported here will enable the design of SLIPS with improved anti‐fouling properties and open the door to new applications of slippery liquid‐infused materials that host or release other active agents.
Slippery, liquid‐infused porous surfaces (SLIPS) that prevent colonization by microbial pathogens and also kill non‐adherent organisms in surrounding media are reported. The approach exploits the polymer and liquid phases in these materials to sustain the release of an antimicrobial agent. This approach improves the inherent anti‐fouling properties of SLIPS, is general in scope, and expands the potential utility of SLIPS in fundamental and applied contexts.
Blocking quorum sensing (QS) pathways has attracted considerable interest as an approach to suppress virulence in bacterial pathogens. Toward this goal, we recently developed analogues of a native ...autoinducing peptide (AIP‐III) signal that can inhibit AgrC‐type QS receptors and attenuate virulence phenotypes in Staphylococcus aureus. Application of these compounds is limited, however, as they contain hydrolytically unstable thioester linkages and have only low aqueous solubilities. Herein, we report amide‐linked AIP analogues with greatly enhanced hydrolytic stabilities and solubilities relative to our prior analogues, whilst maintaining strong potencies as AgrC receptor inhibitors in S. aureus. These compounds represent powerful tools for the study of QS.
Strong words: Lactam analogues of peptidic quorum sensing inhibitors in Staphylococcus aureus have significantly enhanced physical properties, whilst maintaining their strong biological activities. Structural analyses reveal that they adopt conformations similar to their thioester precursors, and corroborate their activities in cell‐based assays for AgrC‐type receptor modulation.
Methods to intercept bacterial quorum sensing (QS) have attracted significant attention as potential anti-infective therapies. Staphylococcus aureus is a major human pathogen that utilizes ...autoinducing peptide (AIP) signals to mediate QS and thereby regulate virulence. S. aureus strains are categorized into four groups (I–IV) according to their AIP signal and cognate extracellular receptor, AgrC. Each group is associated with a certain disease profile, and S. aureus group-III strains are responsible for toxic shock syndrome and have been underestimated in other infections to date. A limited set of non-native AIP analogs have been shown to inhibit AgrC receptors; such compounds represent promising tools to study QS pathways in S. aureus. We seek to expand this set of chemical probes and report herein the first design, synthesis, and biological testing of AIP-III mimetics. A set of non-native peptides was identified that can inhibit all four of the AgrC receptors (I–IV) with picomolar IC50 values in reporter strains. These analogs also blocked hemolysis by wild-type S. aureus group I–IV strainsa virulence trait under the control of QSat picomolar concentrations. Moreover, four of the lead AgrC inhibitors were capable of attenuating the production of toxic shock syndrome toxin-1 (also under the control of QS) by over 80% at nanomolar concentrations in a wild-type S. aureus group-III strain. These peptides represent, to our knowledge, the most potent synthetic inhibitors of QS in S. aureus known, and constitute new and readily accessible chemical tools for the study of the AgrC system and virulence in this deadly pathogen.
Peptoids, or oligomers of N-substituted glycines, are a class of foldamers that have shown extraordinary functional potential since their inception nearly two decades ago. However, the generation of ...well-defined peptoid secondary structures remains a difficult task. This challenge is due, in part, to the lack of a thorough understanding of peptoid sequence–structure relationships and, consequently, an incomplete understanding of the peptoid folding process. We seek to delineate sequence–structure relationships through the systematic study of noncovalent interactions in peptoids and the design of novel amide side chains capable of such interactions. Herein, we report the synthesis and detailed structural analysis of a series of (S)-N-(1-naphthylethyl)glycine (Ns1npe) peptoid homo-oligomers by X-ray crystallography, NMR spectroscopy, and circular dichroism (CD) spectroscopy. Four of these peptoids were found to adopt well-defined structures in the solid state, with dihedral angles similar to those observed in polyproline type I (PPI) peptide helices and in peptoids with α-chiral side chains. The X-ray crystal structure of a representative Ns1npe tetramer revealed an all cis-amide helix, with approximately three residues per turn, and a helical pitch of approximately 6.0 Å. 2D-NMR analysis of the length-dependent Ns1npe series showed that these peptoids have very high overall backbone amide K cis/trans values in acetonitrile, indicative of conformationally homogeneous structures in solution. Additionally, CD spectroscopy studies of the Ns1npe homo-oligomers in acetonitrile and methanol revealed a striking length-dependent increase in ellipticity per amide. These Ns1npe helices represent the most robust peptoid helices to be reported, and the incorporation of (S)-N-(1-naphthylethyl)glycines provides a new approach for the generation of stable helical structure in this important class of foldamers.
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