Synthetic polymers for simultaneous bacterial sequestration and quorum sense interference

Rapid Screening and Synthesis of Abiotic Synthetic Receptors for Selective Bacterial Recognition

The major challenges that impede the preparation of abiotic synthetic receptors designed to feature selective bacterial recognition properties are the complexity, nonrobustness, and environmental adaptability of live microbes. Here, we describe a new rapid screening strategy to determine the optimal polymer formulation on 96-well plates and then produce abiotic synthetic receptors by imprinting the surface marker lipopolysaccharide (LPS) of Gram-negative bacteria. The resulting LPS-imprinted nanoparticles reveal remarkable affinity toward LPS with an equilibrium dissociation constant (K_D) value of 10^-12 M and can distinguish and selectively recognize specific bacteria in whole blood at concentrations down to 10 cells/mL. The incorporation of gold nanorods into imprinted nanoparticles allows selective microbial inactivation based on photothermal treatment. We have also demonstrated that the imprinted nanoparticles with high affinity for bacteria could induce bacteria clustering, drive the expression of quorum-sensing-controlled signal molecules, and eventually enhance the productivity of the cell factory.

Synthesis of Thermoresponsive, Catechol-Rich Poly(ethylene glycol) Brush Polymers for Attenuating Cellular Oxidative Stress

Herein, we report a platform to integrate customizable quantities of catechol units into polymers by reacting caffeic acid carbonic anhydride with polymers having pendant amine groups. Brush poly(ethylene glycol)-caffeamide (PEG-CAF) copolymers based on oligo(ethylene glycol)methyl ether methacrylate (OEGMA₅₀₀) were obtained with a catechol content of approximately 30, 40, and 50 mol % (vs OEGMA content). Owing to the hydrophobicity of the introduced CAF groups, the catechol copolymers exhibited cloud points in the range of 23-46 °C and were used to fabricate thermoresponsive Fe^III metal-phenolic network capsules. Polymers with the highest CAF content (50 mol %) proved most effective for attenuating reactive oxygen species levels in vitro, in co-cultured fibroblasts, and breast cancer cells, even in the presence of an exogenous oxidant source. The reported approach to synthesize customizable catechol materials could be generalized to other amine-functional polymers, with potential biomedical applications such as adhesives or stimuli-responsive drug delivery systems.

Polymer-induced biofilms for enhanced biocatalysis

The intrinsic resilience of biofilms to environmental conditions makes them an attractive platform for biocatalysis, bioremediation, agriculture or consumer health. However, one of the main challenges in these areas is that beneficial bacteria are not necessarily good at biofilm formation. Currently, this problem is solved by genetic engineering or experimental evolution, techniques that can be costly and time consuming, require expertise in molecular biology and/or microbiology and, more importantly, are not suitable for all types of microorganisms or applications. Here we show that synthetic polymers can be used as an alternative, working as simple additives to nucleate the formation of biofilms. Using a combination of controlled radical polymerization and dynamic covalent chemistry, we prepare a set of synthetic polymers carrying mildly cationic, aromatic, heteroaromatic or aliphatic moieties. We then demonstrate that hydrophobic polymers induce clustering and promote biofilm formation in MC4100, a strain of Escherichia coli that forms biofilms poorly, with aromatic and heteroaromatic moieties leading to the best performing polymers. Moreover, we compare the effect of the polymers on MC4100 against PHL644, an E. coli strain that forms biofilms well due to a single point mutation which increases expression of the adhesin curli. In the presence of selected polymers, MC4100 can reach levels of biomass production and curli expression similar or higher than PHL644, demonstrating that synthetic polymers promote similar changes in microbial physiology than those introduced following genetic modification. Finally, we demonstrate that these polymers can be used to improve the performance of MC4100 biofilms in the biocatalytic transformation of 5-fluoroindole into 5-fluorotryptophan. Our results show that incubation with these synthetic polymers helps MC4100 match and even outperform PHL644 in this biotransformation, demonstrating that synthetic polymers can underpin the development of beneficial applications of biofilms.

Glycosylated gold nanoparticles in point of care diagnostics: from aggregation to lateral flow

Current point-of-care lateral flow immunoassays, such as the home pregnancy test, rely on proteins as detection units (e.g. antibodies) to sense for analytes. Glycans play a fundamental role in biological signalling and recognition events such as pathogen adhesion and hence they are promising future alternatives to antibody-based biosensing and diagnostics. Here we introduce the potential of glycans coupled to gold nanoparticles as recognition agents for lateral flow diagnostics. We first introduce the concept of lateral flow, including a case study of lateral flow use in the field compared to other diagnostic tools. We then introduce glycosylated materials, the affinity gains achieved by the cluster glycoside effect and the current use of these in aggregation based assays. Finally, the potential role of glycans in lateral flow are explained, and examples of their successful use given.

Antibody-based lateral flow (immune) assays are well established, but here the emerging concept and potential of using glycans as the detection agents is reviewed.

Nano-Based Drug Delivery or Targeting to Eradicate Bacteria for Infection Mitigation: A Review of Recent Advances

Pathogenic bacteria infection is a major public health problem due to the high morbidity and mortality rates, as well as the increased expenditure on patient management. Although there are several options for antimicrobial therapy, their efficacy is limited because of the occurrence of drug-resistant bacteria. Many conventional antibiotics have failed to show significant amelioration in overall survival of infectious patients. Nanomedicine for delivering antibiotics provides an opportunity to improve the efficiency of the antibacterial regimen. Nanosystems used for antibiotic delivery and targeting to infection sites render some benefits over conventional formulations, including increased solubility, enhanced stability, improved epithelium permeability and bioavailability, prolonged antibiotic half-life, tissue targeting, and minimal adverse effects. The nanocarriers' sophisticated material engineering tailors the controllable physicochemical properties of the nanoparticles for bacterial targeting through passive or active targeting. In this review, we highlight the recent progress on the development of antibacterial nanoparticles loaded with antibiotics. We systematically introduce the concepts and amelioration mechanisms of the nanomedical techniques for bacterial eradication. Passive targeting by modulating the nanoparticle structure and the physicochemical properties is an option for efficient drug delivery to the bacteria. In addition, active targeting, such as magnetic hyperthermia induced by iron oxide nanoparticles, is another efficient way to deliver the drugs to the targeted site. The nanoparticles are also designed to respond to the change in environment pH or enzymes to trigger the release of the antibiotics. This article offers an overview of the benefits of antibacterial nanosystems for treating infectious diseases.

Cell membrane engineering with synthetic materials: Applications in cell spheroids, cellular glues and microtissue formation

Biologically inspired materials with tunable bio- and physicochemical properties provide an essential framework to actively control and support cellular behavior. Cell membrane remodeling approaches benefit from the advances in polymer science and bioconjugation methods, which allow for the installation of un-/natural molecules and particles on the cells' surface. Synthetically remodeled cells have superior properties and are under intense investigation in various therapeutic scenarios as cell delivery systems, bio-sensing platforms, injectable biomaterials and bioinks for 3D bioprinting applications. In this review article, recent advances in the field of cell surface remodeling via bio-chemical means and the potential biomedical applications of these emerging cell hybrids are discussed. STATEMENT OF SIGNIFICANCE: Recent advances in bioconjugation methods, controlled/living polymerizations, microfabrication techniques and 3D printing technologies have enabled researchers to probe specific cellular functions and cues for therapeutic and research purposes through the formation of cell spheroids and polymer-cell chimeras. This review article highlights recent non-genetic cell membrane engineering strategies towards the fabrication of cellular ensembles and microtissues with interest in 3D in vitro modeling, cell therapeutics and tissue engineering. From a wider perspective, these approaches may provide a roadmap for future advances in cell therapies which will expedite the clinical use of cells, thereby improving the quality and accessibility of disease treatments.

Aggregation of Vibrio cholerae by Cationic Polymers Enhances Quorum Sensing but Overrides Biofilm Dissipation in Response to Autoinduction

Vibrio cholerae is a Gram-negative bacterium found in aquatic environments and a human pathogen of global significance. Its transition between host-associated and environmental lifestyles involves the tight regulation of niche-specific phenotypes such as motility, biofilm formation, and virulence. V. cholerae’s transition from the host to environmental dispersal usually involves suppression of virulence and dispersion of biofilm communities. In contrast to this naturally occurring transition, bacterial aggregation by cationic polymers triggers a unique response, which is to suppress virulence gene expression while also triggering biofilm formation by V. cholerae, an artificial combination of traits that is potentially very useful to bind and neutralize the pathogen from contaminated water. Here, we set out to uncover the mechanistic basis of this polymer-triggered bacterial behavior. We found that bacteria–polymer aggregates undergo rapid autoinduction and achieve quorum sensing at bacterial densities far below those required for autoinduction in the absence of polymers. We demonstrate this induction of quorum sensing is due both to a rapid formation of autoinducer gradients and local enhancement of autoinducer concentrations within bacterial clusters as well as the stimulation of CAI-1 and AI-2 production by aggregated bacteria. We further found that polymers cause an induction of the biofilm-specific regulator VpsR and the biofilm structural protein RbmA, bypassing the usual suppression of biofilm during autoinduction. Overall, this study highlights that synthetic materials can be used to cross-wire natural bacterial responses to achieve a combination of phenotypes with potentially useful applications.

Poly(silsesquioxanes) and poly(siloxanes) grafted with N-acetylcysteine for eradicating mature bacterial biofilms in water environment

Bacteria adapt to their living environment forming organised biofilms. The survival strategy makes them more resistant to disinfectants, which results in acute biofilm-caused infections, secondary water pollution by biofilm metabolites and bio-corrosion. New, efficient and environmentally friendly strategies must be developed to solve this problem. Water soluble N-acetyl derivative of L-cysteine (NAC) is a non-toxic compound of mucolytic and bacteriostatic properties that can interfere with the formation of biofilms. However, it can also be a source of C and N for undesired microorganisms, as well as a reason for some adverse human health effects. Consequently, novel procedures are required, that would decrease the take-up of NAC but not reduce its antibacterial properties. We have grafted N-acetyl-l-cysteine onto linear poly(vinylsilsesquioxanes) and poly(methylvinylsiloxanes) via thiol-ene addition. Antibacterial activity of the obtained hybrid materials (respectively, NAC-Si-1 and NAC-Si-2) was determined against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus strains. Native NAC inhibited growth of planktonic cells for the tested bacteria at concentration 0.25% w/v. Inhibition with equivalent solutions of the polymer derivatives was less effective due to the lack of SH groups. However, the tested polymers proved to be quite effective in eradication of mature biofilms. Treatment with 1% w/v emulsions of the hybrid polymers resulted in a significant reduction of viable cells in biofilm matrix despite the absence of thiol moieties. The effect was most pronounced for mature biofilms of S. aureus eradicated with NAC-Si-2.

Transiently malleable multi-healable hydrogel nanocomposites based on responsive boronic acid copolymers

Dynamic multi-responsive gel nanocomposites with rapid self-healing and cell encapsulation properties are presented.

Copolymers enhance selective bacterial community colonization for potential root zone applications

Managing the impact of anthropogenic and climate induced stress on plant growth remains a challenge. Here we show that polymeric hydrogels, which maintain their hydrous state, can be designed to exploit functional interactions with soil microorganisms. This microbial enhancement may mitigate biotic and abiotic stresses limiting productivity. The presence of mannan chains within synthetic polyacrylic acid (PAA) enhanced the dynamics and selectivity of bacterial ingress in model microbial systems and soil microcosms. Pseudomonas fluorescens exhibiting high mannan binding adhesins showed higher ingress and localised microcolonies throughout the polymeric network. In contrast, ingress of Bacillus subtilis, lacking adhesins, was unaltered by mannan showing motility comparable to bulk liquids. Incubation within microcosms of an agricultural soil yielded hydrogel populations significantly increased from the corresponding soil. Bacterial diversity was markedly higher in mannan containing hydrogels compared to both control polymer and soil, indicating enhanced selectivity towards microbial families that contain plant beneficial species. Here we propose functional polymers applied to the potential root zone which can positively influence rhizobacteria colonization and potentially plant growth as a new approach to stress tolerance.

Polymers for binding of the gram-positive oral pathogen Streptococcus mutans

Streptococcus mutans is the most significant pathogenic bacterium implicated in the formation of dental caries and, both directly and indirectly, has been associated with severe conditions such as multiple sclerosis, cerebrovascular and peripheral artery disease. Polymers able to selectively bind S. mutans and/or inhibit its adhesion to oral tissue in a non-lethal manner would offer possibilities for addressing pathogenicity without selecting for populations resistant against bactericidal agents. In the present work two libraries of 2-(dimethylamino)ethyl methacrylate (pDMAEMA)-based polymers were synthesized with various proportions of either N,N,N-trimethylethanaminium cationic- or sulfobetaine zwitterionic groups. These copolymers where initially tested as potential macromolecular ligands for S. mutans NCTC 10449, whilst Escherichia coli MG1655 was used as Gram-negative control bacteria. pDMAEMA-derived materials with high proportions of zwitterionic repeating units were found to be selective for S. mutans, in both isolated and S. mutans-E. coli mixed bacterial cultures. Fully sulfobetainized pDMAEMA was subsequently found to bind/cluster preferentially Gram-positive S. mutans and S. aureus compared to Gram negative E. coli and V. harveyi. A key initial stage of S. mutans pathogenesis involves a lectin-mediated adhesion to the tooth surface, thus the range of potential macromolecular ligands was further expanded by investigating two glycopolymers bearing α-mannopyranoside and β-galactopyranoside pendant units. Results with these polymers indicated that preferential binding to either S. mutans or E. coli can be obtained by modulating the glycosylation pattern of the chosen multivalent ligands without incurring unacceptable cytotoxicity in a model gastrointestinal cell line. Overall, our results allowed to identify a structure-property relationship for the potential antimicrobial polymers investigated, and suggest that preferential binding to Gram-positive S. mutans could be achieved by fine-tuning of the recognition elements in the polymer ligands.

Engineering microbial physiology with synthetic polymers: cationic polymers induce biofilm formation in Vibrio cholerae and downregulate the expression of virulence genes

Here we report the first application of non-bactericidal synthetic polymers to modulate the physiology of a bacterial pathogen. Poly(N-[3-(dimethylamino)propyl] methacrylamide) (P1) and poly(N-(3-aminopropyl)methacrylamide) (P2), cationic polymers that bind to the surface of V. cholerae, the infectious agent causing cholera disease, can sequester the pathogen into clusters. Upon clustering, V. cholerae transitions to a sessile lifestyle, characterised by increased biofilm production and the repression of key virulence factors such as the cholera toxin (CTX). Moreover, clustering the pathogen results in the minimisation of adherence and toxicity to intestinal epithelial cells. Our results suggest that the reduction in toxicity is associated with the reduction to the number of free bacteria, but also the downregulation of toxin production. Finally we demonstrate that these polymers can reduce colonisation of zebrafish larvae upon ingestion of water contaminated with V. cholerae. Overall, our results suggest that the physiology of this pathogen can be modulated without the need to genetically manipulate the microorganism and that this modulation is an off-target effect that results from the intrinsic ability of the pathogen to sense and adapt to its environment. We believe these findings pave the way towards a better understanding of the interactions between pathogenic bacteria and polymeric materials and will underpin the development of novel antimicrobial polymers.

Dendrimer mediated clustering of bacteria: improved aggregation and evaluation of bacterial response and viability

Here, we evaluate how cationic gallic acid-triethylene glycol (GATG) dendrimers interact with bacteria and their potential to develop new antimicrobials. We demonstrate that GATG dendrimers functionalised with primary amines in their periphery can induce the formation of clusters in Vibrio harveyi, an opportunistic marine pathogen, in a generation dependent manner. Moreover, these cationic GATG dendrimers demonstrate an improved ability to induce cluster formation when compared to poly(N-[3-(dimethylamino)propyl]methacrylamide) [p(DMAPMAm)], a cationic linear polymer previously shown to cluster bacteria. Viability of the bacteria within the formed clusters and evaluation of quorum sensing controlled phenotypes (i.e. light production in V. harveyi) suggest that GATG dendrimers may be activating microbial responses by maintaining a high concentration of quorum sensing signals inside the clusters while increasing permeability of the microbial outer membranes. Thus, the reported GATG dendrimers constitute a valuable platform for the development of novel antimicrobial materials that can target microbial viability and/or virulence.

Modulating Vibrio cholerae quorum-sensing-controlled communication using autoinducer-loaded nanoparticles

The rise of bacterial antibiotic resistance has created a demand for alternatives to traditional antibiotics. Attractive possibilities include pro- and anti-quorum sensing therapies that function by modulating bacterial chemical communication circuits. We report the use of Flash NanoPrecipitation to deliver the Vibrio cholerae quorum-sensing signal CAI-1 ((S)-3-hydroxytridecan-4-one) in a water dispersible form as nanoparticles. The particles activate V. cholerae quorum-sensing responses 5 orders of magnitude higher than does the identically administered free CAI-1 and are diffusive across in vivo delivery barriers such as intestinal mucus. This work highlights the promise of combining quorum-sensing strategies with drug delivery approaches for the development of next-generation medicines.

Mussel-inspired protein-repelling ambivalent block copolymers: controlled synthesis and characterization

This paper describes the reversible addition–fragmentation chain transfer (RAFT) polymerization of mussel-inspired acetonide-protected dopamine (meth)acrylamide monomers (ADA and ADMA) and its implementation to the synthesis of innovative ambivalent block copolymers.

Synthesis of Bioinspired Carbohydrate Amphiphiles that Promote and Inhibit Biofilms

The synthesis and characterization of a new class of bioinspired carbohydrate amphiphiles that modulate Pseudomonas aeruginosa biofilm formation are reported. The carbohydrate head is an enantiopure poly-amido-saccharide (PAS) prepared by a controlled anionic polymerization of β-lactam monomers derived from either glucose or galactose. The supramolecular assemblies formed by PAS amphiphiles are investigated in solution using fluorescence assays and dynamic light scattering. Dried samples are investigated using X-ray, infrared spectroscopy, and transmission electron microscopy. Additionally, the amphiphiles are evaluated for their ability to modulate biofilm formation by the Gram-negative bacterium Pseudomonas aeruginosa. Remarkably, from a library of eight amphiphiles, we identify a structure that promotes biofilm formation and two structures that inhibit biofilm formation. Using biological assays and electron microscopy, we relate the chemical structure of the amphiphiles to the observed activity. Materials that modulate the formation of biofilms by bacteria are important both as research tools for microbiologists to study the process of biofilm formation and for their potential to provide new drug candidates for treating biofilm-associated infections.

Bacteria clustering by polymers induces the expression of quorum-sensing-controlled phenotypes

Bacteria deploy a range of chemistries to regulate their behaviour and respond to their environment. Quorum sensing is one method by which bacteria use chemical reactions to modulate pre-infection behaviour such as surface attachment. Polymers that can interfere with bacterial adhesion or the chemical reactions used for quorum sensing are therefore a potential means to control bacterial population responses. Here, we report how polymeric 'bacteria sequestrants', designed to bind to bacteria through electrostatic interactions and therefore inhibit bacterial adhesion to surfaces, induce the expression of quorum-sensing-controlled phenotypes as a consequence of cell clustering. A combination of polymer and analytical chemistry, biological assays and computational modelling has been used to characterize the feedback between bacteria clustering and quorum sensing signalling. We have also derived design principles and chemical strategies for controlling bacterial behaviour at the population level.

Small molecule inhibitors of AI-2 signaling in bacteria: state-of-the-art and future perspectives for anti-quorum sensing agents

Bacteria respond to different small molecules that are produced by other neighboring bacteria. These molecules, called autoinducers, are classified as intraspecies (i.e., molecules produced and perceived by the same bacterial species) or interspecies (molecules that are produced and sensed between different bacterial species). AI-2 has been proposed as an interspecies autoinducer and has been shown to regulate different bacterial physiology as well as affect virulence factor production and biofilm formation in some bacteria, including bacteria of clinical relevance. Several groups have embarked on the development of small molecules that could be used to perturb AI-2 signaling in bacteria, with the ultimate goal that these molecules could be used to inhibit bacterial virulence and biofilm formation. Additionally, these molecules have the potential to be used in synthetic biology applications whereby these small molecules are used as inputs to switch on and off AI-2 receptors. In this review, we highlight the state-of-the-art in the development of small molecules that perturb AI-2 signaling in bacteria and offer our perspective on the future development and applications of these classes of molecules.

Chemical methods to interrogate bacterial quorum sensing pathways

Bacteria frequently manifest distinct phenotypes as a function of cell density in a phenomenon known as quorum sensing (QS). This intercellular signalling process is mediated by "chemical languages" comprised of low-molecular weight signals, known as autoinducers, and their cognate receptor proteins. As many of the phenotypes regulated by QS can have a significant impact on the success of pathogenic or mutualistic prokaryotic-eukaryotic interactions, there is considerable interest in methods to probe and modulate QS pathways with temporal and spatial control. Such methods would be valuable for both basic research in bacterial ecology and in practical medicinal, agricultural, and industrial applications. Toward this goal, considerable recent research has been focused on the development of chemical approaches to study bacterial QS pathways. In this Perspective, we provide an overview of the use of chemical probes and techniques in QS research. Specifically, we focus on: (1) combinatorial approaches for the discovery of small molecule QS modulators, (2) affinity chromatography for the isolation of QS receptors, (3) reactive and fluorescent probes for QS receptors, (4) antibodies as quorum "quenchers," (5) abiotic polymeric "sinks" and "pools" for QS signals, and (6) the electrochemical sensing of QS signals. The application of such chemical methods can offer unique advantages for both elucidating and manipulating QS pathways in culture and under native conditions.