Antimicrobial Polymethacrylates Synthesized as Mimics of Tryptophan-Rich Cationic Peptides

Polyoxometalate-Polymer Directed Macromolecular Architectonics of Silver Nanoparticles as Effective Antimicrobials

A novel inorganic-organic-inorganic ternary bioactive material formulated on antimicrobial peptide-based polymer has been reported. Supramolecular approach has been employed to incorporate molecularly crowded tyrosine-based polymer stabilized silver nanoparticles into membrane bound vesicles exploiting polyoxometalate-triggered surface templating strategy. Utilizing the covalent reversible addition fragmentation chain transfer (RAFT) polymerization and exploiting templated supramolecular architectonics at biopolymer interface, the bioactive ternary polymeric nanohybrids have been designed against Shigellosis leveraging the antibacterial activities of silver nanoparticle, cationic amphiphilic tyrosine polymer and inorganic polyoxometalate. The detail investigation against Shigella flexneri 2a cell line demonstrates that the collaborative mechanism of the ternary hybrid composite enhances the bactericidal activity in comparison to only polyoxometalate and polymer stabilized silver nanoparticle with an altered mechanism of action which is established via detailed biological analysis.

AI-guided few-shot inverse design of HDP-mimicking polymers against drug-resistant bacteria

Host defense peptide (HDP)-mimicking polymers are promising therapeutic alternatives to antibiotics and have large-scale untapped potential. Artificial intelligence (AI) exhibits promising performance on large-scale chemical-content design, however, existing AI methods face difficulties on scarcity data in each family of HDP-mimicking polymers (<102), much smaller than public polymer datasets (>105), and multi-constraints on properties and structures when exploring high-dimensional polymer space. Herein, we develop a universal AI-guided few-shot inverse design framework by designing multi-modal representations to enrich polymer information for predictions and creating a graph grammar distillation for chemical space restriction to improve the efficiency of multi-constrained polymer generation with reinforcement learning. Exampled with HDP-mimicking β-amino acid polymers, we successfully simulate predictions of over 105 polymers and identify 83 optimal polymers. Furthermore, we synthesize an optimal polymer DM0.8iPen0.2 and find that this polymer exhibits broad-spectrum and potent antibacterial activity against multiple clinically isolated antibiotic-resistant pathogens, validating the effectiveness of AI-guided design strategy.

Antibacterial polyurethane foams with quaternized-chitosan as a chain extender for nasal packing and hemostasis

Endoscopic surgery is an effective and common clinical practice for chronic sinusitis. Nasal packing materials are applied in nasal surgery to prevent hemorrhage and promote wound healing. In this study, a degradable polyurethane foam dressing is successfully developed as a promising nasal packing material with good biocompatibility and antibacterial capability. Specifically, quaternized chitosan (QCS) serves as the crosslinker instead of polyols to offer polyurethane foam (PUF-QCS) antibacterial capability. The PUF-QCS2.0 % (with 2.0 wt% QCS) exhibits satisfactory liquid absorption capacity (19.4 g/g), high compressive strengths at both wet (14.5 kPa) and dry states (7.7 kPa), and a good degradation rate (8.3 %) within 7 days. Meanwhile, PUF-QCS2.0 % retains long-term antibacterial activity for 7 days and kills 97.3 % of S. aureus and 91.8 % of E. coli within 6 hours in antibacterial testing. Furthermore, PUF-QCS2.0 % demonstrates a positive hemostatic response in the rabbit nasal septum mucosa trauma model by reducing hemostatic time over 50.0 % and decreasing blood loss up to 76.1 % compared to the commercial PVA nasal packing sponge. Importantly, PUF-QCS also exhibits a significant antibacterial activity in nasal cavity. This nasal packing material has advantages in post-surgery bleeding control and infection prevention. STATEMENT OF SIGNIFICANCE: The performance of a nasal packing sponge requires good mechanical properties, fast and high liquid absorption rate, effective degradability and strong antibacterial activity. These features are helpful for improving the postoperative recovery and patient healing. However, integrating these into a single polyurethane foam is a challenge. In this study, quaternized chitosan (QCS) is synthesized and used as a chain extender and antibacterial agent in preparing a degradable polyurethane foam (PUF-QCS) dressing. PUF-QCS undergoes partial degradation and exhibits effective broad-spectrum antibacterial activity in 7 days. The reduction of postoperative bleeding and infection observed in the animal experiment further demonstrates that the PUF-QCS developed here outperforms the existing commercial nasal packing materials.

One-Pot Three-Component Synthesis of Indolyl-4H-chromene-3-sulfonyl Fluoride: A Class of Important Pharmacophore

A one-pot, sequential three-component reaction between salicylaldehyde, indole, and 2-bromoprop-2-ene-1-sulfonyl fluoride (BPESF) has been demonstrated for the synthesis of sulfonyl fluoride substituted 4H-chromene derivatives in moderate to excellent yields (45%-94%). This one-pot sequential method features easily available starting materials, wide substrate scope, mild conditions, and great efficiency.

pH-Responsive Polymeric Micelle Dynamic Complexes for Selective Killing of Helicobacter pylori

Helicobacter pylori, the world's most common chronic infection-causing pathogen, is responsible for causing gastric ulcers, the fourth-leading cause of cancer-related death globally in 2020. In recent years, the effectiveness of the current treatment regimen (two antibiotics and one proton pump inhibitor) has often been plagued with problems such as resistance and the undesired elimination of commensal bacteria. Herein, we report the synthesis of block and random copolycarbonates, functionalized with cationic guanidinium and anionic acetate functional groups, aimed at selectively killing H. pylori in the acidic environment of the stomach, while remaining nontoxic to the commensal bacteria in the gut. The compositions of the polymers were fine-tuned so that the polymers were readily dispersed in water without any difficulty at both pH 3.0 and 7.4. The self-assembly behavior of the polymers at different pH values by dynamic light scattering showed that the random and block copolymers formed stable micelles in a simulated gastric environment (pH 3.0) while aggregated at pH 7.4. Both polymers demonstrated stronger antibacterial activity against H. pylori than the guanidinium-functionalized homopolymer without any acetate functional group at pH 3.0. The block copolymer was significantly more bactericidal at pH 3.0 across the concentrations tested, as compared to the random copolymer, while it did not show significant toxicity toward rat red blood cells (rRBCs) and HK-2 cells or bactericidal effect toward E. coli (a common gut bacterium) and nor caused aggregation of rRBCs at its effective concentration and at physiological pH of 7.4. Additionally, both the block and random copolymers were much more stable against hydrolysis at pH 3.0 than at pH 7.4. This study provides insight into the influence of both polymer architecture and dynamic assembly on the bioactivities of antimicrobial polymers, where the disassembly of coacervates into narrowly dispersed micelles at pH 3 make them potent antimicrobials aided by the protonated carboxylic acid block.

The Potential Role of Ionic Liquid as a Multifunctional Dental Biomaterial

In craniofacial research and routine dental clinical procedures, multifunctional materials with antimicrobial properties are in constant demand. Ionic liquids (ILs) are one such multifunctional intelligent material. Over the last three decades, ILs have been explored for different biomedical applications due to their unique physical and chemical properties, high task specificity, and sustainability. Their stable physical and chemical characteristics and extremely low vapor pressure make them suitable for various applications. Their unique properties, such as density, viscosity, and hydrophilicity/hydrophobicity, may provide higher performance as a potential dental material. ILs have functionalities for optimizing dental implants, infiltrate materials, oral hygiene maintenance products, and restorative materials. They also serve as sensors for dental chairside usage to detect oral cancer, periodontal lesions, breath-based sobriety, and dental hard tissue defects. With further optimization, ILs might also make vital contributions to craniofacial regeneration, oral hygiene maintenance, oral disease prevention, and antimicrobial materials. This review explores the different advantages and properties of ILs as possible dental material.

Biomimetic antimicrobial polymers—Design, characterization, antimicrobial, and novel applications

Biomimetic antimicrobial polymers have been an area of great interest as the need for novel antimicrobial compounds grows due to the development of resistance. These polymers were designed and developed to mimic naturally occurring antimicrobial peptides in both physicochemical composition and mechanism of action. These antimicrobial peptide mimetic polymers have been extensively investigated using chemical, biophysical, microbiological, and computational approaches to gain a deeper understanding of the molecular interactions that drive function. These studies have helped inform SARs, mechanism of action, and general physicochemical factors that influence the activity and properties of antimicrobial polymers. However, there are still lingering questions in this field regarding 3D structural patterning, bioavailability, and applicability to alternative targets. In this review, we present a perspective on the development and characterization of several antimicrobial polymers and discuss novel applications of these molecules emerging in the field. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Antimicrobial Peptides and Macromolecules for Combating Microbial Infections: From Agents to Interfaces

Bacterial resistance caused by the overuse of antibiotics and the shelter of biofilms has evolved into a global health crisis, which drives researchers to continuously explore antimicrobial molecules and strategies to fight against drug-resistant bacteria and biofilm-associated infections. Cationic antimicrobial peptides (AMPs) are considered to be a category of potential alternative for antibiotics owing to their excellent bactericidal potency and lesser likelihood of inducing drug resistance through their distinctive antimicrobial mechanisms. In this review, the hitherto reported plentiful action modes of AMPs are systematically classified into 15 types and three categories (membrane destructive, nondestructive membrane disturbance, and intracellular targeting mechanisms). Besides natural AMPs, cationic polypeptides, synthetic polymers, and biopolymers enable to achieve tunable antimicrobial properties by optimizing their structures. Subsequently, the applications of these cationic antimicrobial agents at the biointerface as contact-active surface coatings and multifunctional wound dressings are also emphasized here. At last, we provide our perspectives on the development of clinically significant cationic antimicrobials and related challenges in the translation of these materials.

Quaternized Amphiphilic Block Copolymers as Antimicrobial Agents

In this study, a novel polystyrene-block-quaternized polyisoprene amphipathic block copolymer (PS-b-PIN) is derived from anionic polymerization. Quaternized polymers are prepared through post-quaternization on a functionalized polymer side chain. Moreover, the antibacterial activity of quaternized polymers without red blood cell (RBCs) hemolysis can be controlled by block composition, side chain length, and polymer morphology. The solvent environment is highly related to the polymer morphology, forming micelles or other structures. The polymersome formation would decrease the hemolysis and increase the electron density or quaternized groups density as previous research and our experiment revealed. Herein, the PS-b-PIN with N,N-dimethyldodecylamine as side chain would form a polymersome structure in the aqueous solution to display the best inhibiting bacterial growth efficiency without hemolytic effect. Therefore, the different single-chain quaternized groups play an important role in the antibacterial action, and act as a controllable factor.

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Nonionic nontoxic antimicrobial polymers: indole-grafted poly(vinyl alcohol) with pendant alkyl or ether groups

A series of new nonionic antimicrobial polymers with a biodegradable polyvinyl alcohol (PVA) backbone grafted with indole units and different hydrophobic alkyl or ether groups were synthesized by facile esterification.

AIEgens for Bacterial Imaging and Ablation

Accurate and sensitive diagnosis of pathogenic bacterial infection is a fundamental first step for correct bacteria management, helping to avoid the development of drug-resistant bacteria caused by the inappropriate use and overuse of antibiotics. Fluorescence probes as a promising visual tool can help identify pathogens rapidly and reliably. However, rigidly structured traditional fluorescence probes generally suffer from the drawback of aggregation-caused quenching (ACQ) effect, which greatly undermines their advantages with respect to sensitivity. Luminogens with aggregation-induced emission properties, namely AIEgens, can overcome the ACQ effect and certain AIEgen-based materials are capable of generating reactive oxygen species (ROS) in the aggregate states. Hence, they have become powerful tools for imaging and killing bacteria. This review summarizes the recent advances in AIEgens for the diagnosis and treatment of pathogen infections. Special attention has been paid to the molecular design, the application in bacterial imaging and ablation in vitro and in vivo, and the biocompatibility of AIEgens. Finally, the challenges and prospects are discussed in terms of using AIEgens to advance precision therapies for pathogen infections.

Nanotechnology as a Novel Approach in Combating Microbes Providing an Alternative to Antibiotics

The emergence of infectious diseases promises to be one of the leading mortality factors in the healthcare sector. Although several drugs are available on the market, newly found microorganisms carrying multidrug resistance (MDR) against which existing drugs cannot function effectively, giving rise to escalated antibiotic dosage therapies and the need to develop novel drugs, which require time, money, and manpower. Thus, the exploitation of antimicrobials has led to the production of MDR bacteria, and their prevalence and growth are a major concern. Novel approaches to prevent antimicrobial drug resistance are in practice. Nanotechnology-based innovation provides physicians and patients the opportunity to overcome the crisis of drug resistance. Nanoparticles have promising potential in the healthcare sector. Recently, nanoparticles have been designed to address pathogenic microorganisms. A multitude of processes that can vary with various traits, including size, morphology, electrical charge, and surface coatings, allow researchers to develop novel composite antimicrobial substances for use in different applications performing antimicrobial activities. The antimicrobial activity of inorganic and carbon-based nanoparticles can be applied to various research, medical, and industrial uses in the future and offer a solution to the crisis of antimicrobial resistance to traditional approaches. Metal-based nanoparticles have also been extensively studied for many biomedical applications. In addition to reduced size and selectivity for bacteria, metal-based nanoparticles have proven effective against pathogens listed as a priority, according to the World Health Organization (WHO). Moreover, antimicrobial studies of nanoparticles were carried out not only in vitro but in vivo as well in order to investigate their efficacy. In addition, nanomaterials provide numerous opportunities for infection prevention, diagnosis, treatment, and biofilm control. This study emphasizes the antimicrobial effects of nanoparticles and contrasts nanoparticles' with antibiotics' role in the fight against pathogenic microorganisms. Future prospects revolve around developing new strategies and products to prevent, control, and treat microbial infections in humans and other animals, including viral infections seen in the current pandemic scenarios.

Macromolecular Nanotherapeutics and Antibiotic Adjuvants to Tackle Bacterial and Fungal Infections

The escalating rise in the population of multidrug-resistant (MDR) pathogens coupled with their biofilm forming ability has struck the global health as nightmare. Alongwith the threat of aforementioned menace, the sluggish development of new antibiotics and the continuous deterioration of the antibiotic pipeline has stimulated the scientific community toward the search of smart and innovative alternatives. In near future, membrane targeting antimicrobial polymers, inspired from antimicrobial peptides, can stand out significantly to combat against the MDR superbugs. Many of these amphiphilic polymers can form nanoaggregates through self-assembly with superior and selective antimicrobial efficacy. Additionally, these macromolecular nanoaggregrates can be utilized to engineer smart antibiotic-delivery system for on-demand drug-release, exploiting the infection site's micoenvironment. This strategy substantially increases the local concentration of antibiotics and reduces the associated off-target toxicity. Furthermore, amphiphilc macromolecules can be utilized to rejuvinate obsolete antibiotics to tackle the drug-resistant infections. This review article highlights the recent developments in macromolecular architecture to design numerous nanostructures with broad-spectrum antimicrobial activity, their application in fabricating smart drug delivery systems and their efficacy as antibiotic adjuvants to circumvent antimicrobial resistance. Finally, the current challenges and future prospects are briefly discussed for further exploration and their practical application in clinical settings.

The function of peptide-mimetic anionic groups and salt bridges in the antimicrobial activity and conformation of cationic amphiphilic copolymers

Herein we report the synthesis of ternary statistical methacrylate copolymers comprising cationic ammonium (amino-ethyl methacrylate: AEMA), carboxylic acid (propanoic acid methacrylate: PAMA) and hydrophobic (ethyl methacrylate: EMA) side chain monomers, to study the functional role of anionic groups on their antimicrobial and hemolytic activities as well as the conformation of polymer chains. The hydrophobic monomer EMA was maintained at 40 mol% in all the polymers, with different percentages of cationic ammonium (AEMA) and anionic carboxylate (PAMA) side chains, resulting in different total net charge for the polymers. The antimicrobial and hemolytic activities of the copolymer were determined by the net charge of +3 or larger, suggesting that there was no distinct effect of the anionic carboxylate groups on the antimicrobial and hemolytic activities of the copolymers. However, the pH titration and atomic molecular dynamics simulations suggest that anionic groups may play a strong role in controlling the polymer conformation. This was achieved via formation of salt bridges between cationic and anionic groups, transiently crosslinking the polymer chain allowing dynamic switching between compact and extended conformations. These results suggest that inclusion of functional groups in general, other than the canonical hydrophobic and cationic groups in antimicrobial agents, may have broader implications in acquiring functional structures required for adequate antimicrobial activity. In order to explain the implications, we propose a molecular model in which formation of intra-chain, transient salt bridges, due to the presence of both anionic and cationic groups along the polymer, may function as "adhesives" which facilitate compact packing of the polymer chain to enable functional group interaction but without rigidly locking down the overall polymer structure, which may adversely affect their functional roles.

Efficacy of Ethanolic Extract of Syzygium aromaticum in the Treatment of Multidrug-Resistant Pseudomonas aeruginosa Clinical Isolates Associated with Urinary Tract Infections

Pseudomonas aeruginosa is an organism commonly found in the environment and one of the most common causes of human urinary tract infections in developed and developing countries. The present study aimed to investigate the effect of five medicinal plant extracts on the isolated drug-resistant P. aeruginosa clinical isolates. A total of 100 urine samples were collected from Nagaa Hammadi and Qena General Hospitals and private medical analysis laboratories in Qena governorate, Upper Egypt. Samples were screened for the prevalence of UTI pathogens by biochemical tests, antibiotics sensitivity, detection of virulence, and antibiotic-resistant genes by using multiplex PCR. P. aeruginosa is by far the subdominant causative agent with a percentage of 14%. Clinical isolates were multidrug-resistant, containing bla TEM, bla SHV, toxA, lasB, pslA, and fliC resistant and virulence genes. Based on bioactivity, the ethanolic extract of clove (Syzygium aromaticum) was the most active extract among tested medicinal plants and had the maximum zone of inhibition sized 23 mm against tested bacteria. The results of the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) showed a high decrease of inhibition within a concentration range of (10 to 121.25 mg/mL and 20 to 30 mg/mL, respectively). Further, major compounds of oleic acid (27.22%), guanosine (8.91%), indole (6.83%), 1-eicosene (6.30%), and cis-10-nonadecenoic acid (5.37%) were determined among 12 bioactive compounds in the ethanolic extract of S. aromaticum using gas chromatography-mass spectrometry (GC-MS). These results indicated that the ethanolic extract of S. aromaticum is a promising antibacterial agent for further studies aiming to control bacterial infections including MDR bacteria and develop novel therapeutic alternatives for the treatment of UTI.

Broad-Spectrum Bactericidal Activity of a Synthetic Random Copolymer Based on 2-Methoxy-6-(4-Vinylbenzyloxy)-Benzylammonium Hydrochloride

Low-molecular-weight organic ammonium salts exert excellent antimicrobial effects by interacting lethally with bacterial membranes. Unfortunately, short-term functionality and high toxicity limit their clinical application. On the contrary, the equivalent macromolecular ammonium salts, derived from the polymerization of monomeric ammonium salts, have demonstrated improved antibacterial potency, a lower tendency to develop resistance, higher stability, long-term activity, and reduced toxicity. A water-soluble non-quaternary copolymeric ammonium salt (P7) was herein synthetized by copolymerizing 2-methoxy-6-(4-vinylbenzyloxy)-benzylammonium hydrochloride monomer with N, N-di-methyl-acrylamide. The antibacterial activity of P7 was assessed against several multidrug-resistant (MDR) clinical isolates of both Gram-positive and Gram-negative species. Except for colistin-resistant Pseudomonas aeruginosa, most isolates were susceptible to P7, also including some Gram-negative bacteria with a modified charge in the external membrane. P7 showed remarkable antibacterial activity against isolates of Enterococcus, Staphylococcus, Acinetobacter, and Pseudomonas, and on different strains of Escherichia coli and Stenotrophomonas maltophylia, regardless of their antibiotic resistance. The lowest minimal inhibitory concentrations (MICs) observed were 0.6-1.2 µM and the minimal bactericidal concentrations (MBC) were frequently overlapping with the MICs. In 24-h time-kill and turbidimetric studies, P7 displayed a rapid non-lytic bactericidal activity. P7 could therefore represent a novel and potent tool capable of counteracting infections sustained by several bacteria that are resistant to the presently available antibiotics.

Synthesis, Characterization, and Bactericidal Activity of a 4-Ammoniumbuthylstyrene-Based Random Copolymer

The growing resistance of bacteria to current chemotherapy is a global concern that urgently requires new and effective antimicrobial agents, aimed at curing untreatable infection, reducing unacceptable healthcare costs and human mortality. Cationic polymers, that mimic antimicrobial cationic peptides, represent promising broad-spectrum agents, being less susceptible to develop resistance than low molecular weight antibiotics. We, thus, designed, and herein report, the synthesis and physicochemical characterization of a water-soluble cationic copolymer (P5), obtained by copolymerizing the laboratory-made monomer 4-ammoniumbuthylstyrene hydrochloride with di-methyl-acrylamide as uncharged diluent. The antibacterial activity of P5 was assessed against several multi-drug-resistant clinical isolates of both Gram-positive and Gram-negative species. Except for strains characterized by modifications of the membrane charge, most of the tested isolates were sensible to the new molecule. P5 showed remarkable antibacterial activity against several isolates of genera Enterococcus, Staphylococcus, Pseudomonas, Klebsiella, and against Escherichia coli, Acinetobacter baumannii and Stenotrophomonas maltophilia, displaying a minimum MIC value of 3.15 µM. In time-killing and turbidimetric studies, P5 displayed a rapid non-lytic bactericidal activity. Due to its water-solubility and wide bactericidal spectrum, P5 could represent a promising novel agent capable of overcoming severe infections sustained by bacteria resistant the presently available antibiotics.

Effect of Non-natural Hydrophobic Amino Acids on the Efficacy and Properties of the Antimicrobial Peptide C18G

Antimicrobial peptides (AMPs) have been an area of great interest, due to the high selectivity of these molecules toward bacterial targets over host cells and the limited development of bacterial resistance to these molecules through evolution. The peptides are known to selectively bind to bacterial cell surfaces through electrostatic interactions, and subsequently, the peptides insert into the cell membrane and cause local disruptions of membrane integrity leading to cell death. Previous experiments showed that replacing the Leu residues in the AMP C18G with other naturally occurring hydrophobic residues resulted in side-chain-dependent activities. This work extends the investigation to non-natural hydrophobic amino acids and the effect on peptide activity. Minimal inhibitory concentration (MIC) results demonstrated that amino acid substitutions containing long flexible carbon chains maintained or increased antimicrobial activity compared to natural analogues. In solution, the peptide showed aggregation only with the most hydrophobic non-natural amino acid substitutions. Binding assays using Trp fluorescence confirm a binding preference for anionic lipids while quenching experiments demonstrated that the more hydrophobic peptides are more deeply buried in the anionic lipid bilayers compared to the zwitterionic bilayers. The most effective peptides at killing bacteria were also those which showed some level of disruption of bacterial membranes; however, one peptide sequence exhibited very strong activity and very low levels of red blood cell hemolysis, yielding a promising target for future development.

Recent Progress in Bile Acid-Based Antimicrobials

With the emergence of drug-resistant bacteria and the formation of biofilms by bacteria and fungi, microbial infections gradually threaten global health. Natural antimicrobial peptides (AMPs) have low susceptibility for developing resistance due to the membrane targeted mechanism, but instability and high manufacturing cost limit their applications in clinic. Bile acids, a group of steroids in the human body, with high stability, biocompatibility, and inherent facial amphiphilic structure similar to the characteristics of AMPs, have been applied to the biological field, such as drug delivery systems, self-healing hydrogels, antimicrobials, and so on. In this review, we mainly focus on the different classes of bile acid-based antimicrobials in recent years. Various designs and methods for the preparation of unimolecular antimicrobials with bile acid skeletons are first introduced, including coupling of primary amine, quaternary ammonium, and amino acid units with bile acid skeletons. Some representative oligomeric antimicrobials, including dimers of bile acids, are summarized. Finally, macromolecular antimicrobials bearing some positive charges at the main chain or side chain and interaction mechanisms of these bile acid-based antimicrobials are discussed.

Characteristics and therapeutic applications of antimicrobial peptides

The demand for novel antimicrobial compounds is rapidly growing due to the phenomenon of antibiotic resistance in bacteria. In response, numerous alternative approaches are being taken including use of polymers, metals, combinatorial approaches, and antimicrobial peptides (AMPs). AMPs are a naturally occurring part of the immune system of all higher organisms and display remarkable broad-spectrum activity and high selectivity for bacterial cells over host cells. However, despite good activity and safety profiles, AMPs have struggled to find success in the clinic. In this review, we outline the fundamental properties of AMPs that make them effective antimicrobials and extend this into three main approaches being used to help AMPs become viable clinical options. These three approaches are the incorporation of non-natural amino acids into the AMP sequence to impart better pharmacological properties, the incorporation of AMPs in hydrogels, and the chemical modification of surfaces with AMPs for device applications. These approaches are being developed to enhance the biocompatibility, stability, and/or bioavailability of AMPs as clinical options.

Investigation of the Role of Aromatic Residues in the Antimicrobial Peptide BuCATHL4B

BACKGROUND

Antimicrobial Peptides (AMPs) are an attractive alternative to traditional small molecule antibiotics as AMPs typically target the bacterial cell membrane. A Trp-rich peptide sequence derived from water buffalo (Bubalus bubalis), BuCATHL4B was previously identified as a broad-spectrum antimicrobial peptide.

OBJECTIVE

In this work, native Trp residues were replaced with other naturally occurring aromatic amino acids to begin to elucidate the importance of these residues on peptide activity.

METHODS

Minimal Inhibitory Concentration (MIC) results demonstrated activity against seven strains of bacteria. Membrane and bilayer permeabilization assays were performed to address the role of bilayer disruption in the activity of the peptides. Lipid vesicle binding and quenching experiments were also performed to gain an understanding of how the peptides interacted with lipid bilayers.

RESULTS

MIC results indicate the original, tryptophan-rich sequence, and the phenylalanine substituted sequences exhibit strong inhibition of bacterial growth. In permeabilization assays, peptides with phenylalanine substitutions have higher levels of membrane permeabilization than those substituted with tyrosine. In addition, one of the two-tyrosine substituted sequence, YWY, behaves most differently in the lowest antimicrobial activity, showing no permeabilization of bacterial membranes. Notably the antimicrobial activity is inherently species dependent, with varying levels of activity against different bacteria.

CONCLUSION

There appears to be little correlation between membrane permeabilization and activity, indicating these peptides may have additional mechanisms of action beyond membrane disruption. The results also identify two sequences, denoted FFF and YYW, which retain antibacterial activity but have markedly reduced hemolytic activity.

Amphiphilic polymer therapeutics: an alternative platform in the fight against antibiotic resistant bacteria

Amphiphilic antimicrobial polymers show promising potential as polymer therapeutics to fight drug resistant bacteria and biofilms.

Amino acid acrylamide mimics: creation of a consistent monomer library and characterization of their polymerization behaviour

A novel consistent approach to mimic the structure of biopolymers via precision polymer synthesis with reversible deactivation radical polymerization (RDRP).

Synthetic Polypeptide Polymers as Simplified Analogues of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are naturally occurring macromolecules made of amino acids that are potent broad-spectrum antibiotics with potential as novel therapeutic agents. This review aims to summarize the fundamental principles concerning the structure and mechanism of action of these AMPs, in order to guide the design of polymeric analogues that organic chemistry can generate. Among those simplified analogues, this review particularly focuses on those made of amino acids called polypeptide polymers: they are showing great potential by providing one of the best biomimetic and bioactive structures for further biomaterials science applications.

Efficacy of imidazolium and piperidinium based ionic liquids on inhibiting biofilm formation on titanium and carbon steel surfaces

In the present study, the efficacies of three different cationic and anionic ionic liquids (ILs) on biofilm formation on materials used in cooling water systems were evaluated. Two imidazolium based ILs; 1-Ethyl 3-Methylimidazolium tetrafluoroborate - (IL-E) and 1-Butyl-3-methylimidazolium chloride - (IL-I) with anionic fluoride and chloride groups and one piperidinium based IL, N-methyl-N-propylpiperidinium bis(trifluoromethylsulfonyl)imide - (IL-M) with fluoromethyl group as anion were used. The efficacy of these ILs were evaluated on planktonic and sessile cells of major biofilm formers in cooling water systems using Gram negative bacterium Pseudomonas sp. and Gram positive bacterium Bacillus sp. Further their effect on inhibiting biofilm formation on titanium and carbon steel surfaces were also evaluated. Results showed that planktonic cells of Pseudomonas sp. and Bacillus sp. were effectively inhibited by 25 ppm of IL-M and IL-E, respectively. For both bacteria, 50 ppm of IL-I was enough to inhibit and eradicate the sessile cell formation. Among the three ILs, IL-E was the best in inhibiting the adhesion of bacterial cells on Ti and CS surfaces. These results suggest that Imidazolium based ILs are effective in controlling sessile cell formation and eradicating mature biofilm as compared to piperidinium based IL. Further, Imidazolium based IL with fluoride anion (IL-E) was the best in inhibiting adhesion of these bacterial cells and thereby biofilm formation on material surfaces. This study establishes the feasibility of using ILs in cooling water system for bacterial biofilm control along with other conventional biofouling control methods.

Guanidinylated Amphiphilic Polycarbonates with Enhanced Antimicrobial Activity by Extending the Length of the Spacer Arm and Micelle Self-Assembly

Nine guanidinylated amphiphilic polycarbonates are rationally designed and synthesized. Each polymer has the same biodegradable backbone but different side groups. The influence of the hydrophobic/hydrophilic effect on antimicrobial activities and cytotoxicity is systematically investigated. The results verify that tuning the length of the spacer arm between the cationic guanidine group and the polycarbonate backbone is an efficient design strategy to alter the hydrophobic/hydrophilic balance without changing the cationic charge density. A spacer arm of six methylene units (CH₂ )₆ shows the best antimicrobial activity (minimum inhibitory concentration, MIC = 40 µg mL^-1 against Escherichia coli, MIC = 20 µg mL^-1 against Staphylococcus aureus, MIC = 40 µg mL^-1 against Candida albicans) with low hemolytic activity (HC₅₀ > 2560 µg mL^-1 ). Furthermore, the guanidinylated polycarbonates exhibit the ability to self-assemble and present micelle-like nanostructure due to their intrinsic amphiphilic macromolecular structure. Transmission electron microscopy and dynamic light scattering measurements confirm polymer micelle formation in aqueous solution with sizes ranging from 82 to 288 nm.

Bacterial membrane permeability of antimicrobial polymethacrylates: Evidence for a complex mechanism from super-resolution fluorescence imaging

Amphiphilic polymers bearing cationic moieties are an emerging alternative to traditional antibiotics given their broad-spectrum activity and low susceptibility to the development of resistance. To date, however, much remains unclear regarding their mechanism of action. Using functional assays (ATP leakage, cell viability, DNA binding) and super-high resolution structured illumination microscopy (OMX-SR) of fluorescently tagged polymers, we present evidence for a complex mechanism, involving membrane permeation as well as cellular uptake, interaction with intracellular targets and possible complexation with bacterial DNA. STATEMENT OF SIGNIFICANCE: This manuscript details the first study to systematically and directly investigate the mechanism of action of antimicrobial polymers, using super-resolution fluorescence imaging as well as functional assays. While many in the field cite membrane permeation as the sole mechanism underlying the activity of such polymers, we present evidence for multimodal actions including high cellular uptake and interaction with intracellular targets. It is also the first report to show competitive binding of antimicrobial polymers with bacterial DNA in a dose-dependent manner.

Aggregation of methacrylate-based ternary biomimetic antimicrobial polymers in solution

Using detailed atomistic simulations, we explore the morphological characteristics of aggregates formed in solution phase by ternary biomimetic antimicrobial (AM) methacrylate polymers, composed of hydrophobic, charged cationic and polar functional groups and compare it with aggregate morphologies of binary methacrylate polymers, composed only of hydrophobic and charged cationic functional groups. The effect of sequence of the constituent functional groups on aggregate conformation is also studied by considering random and block sequences along the polymer backbone. Our results show that while binary polymers tend to form robust aggregates, replacing some of the hydrophobic groups with overall charge neutral polar groups weakens the aggregate considerably, leading to increased conformational fluctuations and formation of loose-packed, open aggregates, particularly in the case of random ternary polymers. Interaction energy calculations clearly suggest that the role of inclusion of polar groups in ternary polymers is two-fold: (1) to reduce possible strong local concentration of hydrophobic groups and 'smear' the overall hydrophobicity along the polymer backbone to increase the solubility of the polymers (2) to compensate the loss of attractive hydrophobic interactions by forming attractive electrostatic interactions with the charged groups and contribute to aggregation formation, albeit weak. Given that most of the naturally occurring AM peptides have contributions from all the three functional groups, this study elucidates the functionally tuneable role of inclusion of polar groups in the way AM agents interact with each other in solution phase, which can eventually dictate their partitioning behaviour into bacterial and mammalian membranes.

Chemiluminescent self-reporting supramolecular transformations on macromolecular scaffolds

We introduce the synthesis of a self-reporting system with chemiluminescent output, which is regulated via dynamic supramolecular complex formation.

Nanoengineered Antibacterial Coatings and Materials: A Perspective

This feature article begins by outlining the problem of infection and its implication on healthcare. The initial introductory section is followed by a description of the four distinct classes of antibacterial coatings and materials, i.e., bacteria repealing, contact killing, releasing and responsive, that were developed over the years by our team and others. Specific examples of each individual class of antibacterial materials and a discussion on the pros and cons of each strategy are provided. The article contains a dedicated section focused on silver nanoparticle based coatings and materials, which have attracted tremendous interest from the scientific and medical communities. The article concludes with the author’s view regarding the future of the field.

Aggregation-induced emission-based ionic liquids for bacterial killing, imaging, cell labeling, and bacterial detection in blood cells

A series of aggregation-induced emission (AIE)-based imidazolium-type ionic liquids (ILs) were designed and synthesized for bacterial killing and imaging, cell labeling, and bacterial detection in blood cells. The AIE-based ILs showed antibacterial activities against both Escherichia coli and Staphylococcus aureus. The carbon chain length of substitution at the N3 position of the imidazolium cations highly affects the antibacterial properties of ILs. Owing to their AIE characteristics, the ILs could selectively capture fluorescence image of dead bacteria while killing the bacteria. The fluorescence intensity varied with the concentration of bacteria, indicating that AIE-based ILs has potential as an antibacterial material and an efficient probe for bacterial viability assay. In addition, the synthesized AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling, as well as bacterial detection in blood cells. STATEMENT OF SIGNIFICANCE: Bacteria are ubiquitous, especially the pathogenic bacteria, which pose a serious threat to human health. There is an urgent need for materials with efficient antibacterial properties and biocompatibility and without causing drug resistance. In this work, we synthesized a series of aggregation-induced emission (AIE)-doped imidazolium type ionic liquids (ILs) with multifunction potential of bacterial killing and imaging, cell labeling, and detection of bacteria from blood cells. The synthesized AIE-based ILs can image dead bacteria at the same time of killing these bacteria, which can avoid the fluorescent dyeing process. Simultaneously, the fluorescent imaging of dead bacteria can be distinguished by the naked eye, and the fluorescence intensity from the AIE-based ILs varied with the concentration of bacteria. In addition, the AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling as well as detection of bacteria from red blood cell suspension.

Star-shaped polypeptides exhibit potent antibacterial activities

Peptide-based biomaterials are a promising class of antimicrobial agents that work by physically damaging bacterial cell membranes rather than targeting intracellular factors, resulting in less susceptibility to drug resistance. Herein we report the synthesis of cationic, star-shaped polypeptides with 3 to 8 arms and their evaluation as antimicrobial agents against different types of bacteria. The effects of the arm number and side chain group on their antimicrobial activities were systematically investigated. Compared to their linear counterparts, these star-shaped polypeptides exhibited potent antibacterial activity (which may involve adhesion and disruption processes). The increase of the arm number can efficiently increase the antibacterial activities up until 8 arms, which did not exhibit further improvement of antibacterial activities. Poly(l-lysine) (PLL) modified with an indole group (PLL-g-indo) exhibited the best antibacterial activity among all grafted copolypeptides and improved cytotoxic selectivity towards pathogens over mammalian cells without compromising their hemolytic activities. In vivo studies showed that the star-shaped PLL-g-indo can effectively suppress Enterohaemorrhagic E. coli (EHEC) infection and attenuate the clinical symptoms in mice, suggesting that they are promising antimicrobial agents.

Targeting intracellular, multi-drug resistant Staphylococcus aureus with guanidinium polymers by elucidating the structure-activity relationship

Intracellular persistence of bacteria represents a clinical challenge as bacteria can thrive in an environment protected from antibiotics and immune responses. Novel targeting strategies are critical in tackling antibiotic resistant infections. Synthetic antimicrobial peptides (SAMPs) are interesting candidates as they exhibit a very high antimicrobial activity. We first compared the activity of a library of ammonium and guanidinium polymers with different sequences (statistical, tetrablock and diblock) synthesized by RAFT polymerization against methicillin-resistant S. aureus (MRSA) and methicillin-sensitive strains (MSSA). As the guanidinium SAMPs were the most potent, they were used to treat intracellular S. aureus in keratinocytes. The diblock structure was the most active, reducing the amount of intracellular MSSA and MRSA by two-fold. We present here a potential treatment for intracellular, multi-drug resistant bacteria, using a simple and scalable strategy.

Integrated Endotoxin Adsorption and Antibacterial Properties of Cationic Polyurethane Foams for Wound Healing

Gram-negative bacteria, containing toxic proinflammatory and pyrogenic substances [endotoxin or lipopolysaccharide (LPS)], can lead to infection and associated serious diseases, such as sepsis and septic shock. Development of antimicrobial materials with intrinsically endotoxin adsorption activity can prevent the release of bacterial toxic components while killing bacteria. Herein, a series of imidazolium-type polyurethane (PU) foams with antimicrobial properties were synthesized. The content effects of cationic moieties on the antimicrobial activities against Gram-negative Escherichia coli and Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus as well as the endotoxin adsorption property were investigated. The obtained PU foams show slightly higher efficiency against two Gram-negative strains than for Gram-positive one and high absorbability of LPS. A wound healing test using P. aeruginosa and its isolated LPS-treated mice as the models further demonstrated that imidazolium-type PU foams combine both antibacterial and endotoxin adsorption properties and may have a potential application as an antimicrobial wound dressing in a clinical setting.

Strategies from nature: polycaprolactone-based mimetic antimicrobial peptide block copolymers with low cytotoxicity and excellent antibacterial efficiency

PCL₁₆-b-K_n diblock copolymers exhibit excellent antibacterial activities and low cytotoxicity. Meanwhile, they act by the pore-forming bactericidal mechanism without inducement of drug resistance.

Tyrosine based cationic acrylates as potent antimicrobial agents against shigellosis

Design of tyrosine-based cationic polymers with antimicrobial activities.

Antibacterial activities of N-alkyl imidazolium-based poly(ionic liquid) nanoparticles

N-Alkyl imidazolium-based PIL nanoparticles can effectively kill bacteria through adhering to the bacterial surface and then disrupting the cell membrane.

Decoupling the Functional Roles of Cationic and Hydrophobic Groups in the Antimicrobial and Hemolytic Activities of Methacrylate Random Copolymers

In this study, we report the antimicrobial and hemolytic activities of ternary statistical methacrylate copolymers consisting of cationic ammonium (amino-ethyl methacrylate: AEMA), hydrophobic alkyl (ethyl methacrylate: EMA), and neutral hydroxyl (hydroxyethyl methacrylate: HEMA) side chain monomers. The cationic and hydrophobic functionalities of copolymers mimic the cationic amphiphilicity of naturally occurring antimicrobial peptides (AMPs). The HEMA monomer units were used to separately modulate the compositions of cationic and hydrophobic monomers, and we investigated the effect of each component on the antimicrobial and hemolytic activities of copolymers. Our data indicated that increasing the number of cationic groups of the copolymers to be more than 30 mol % did not increase their antimicrobial activity against Escherichia coli. The number of cationic side chains in a polymer chain at this threshold is 5.5-7.7, which is comparable to those of natural antimicrobial peptides such as maginin (+6). The MIC values of copolymers with >30 mol % of AEMA depend on only the mol % of EMA, indicating that the hydrophobic interactions of the copolymers with E. coli cell membranes determine the antimicrobial activity of copolymers. These results suggest that the roles of cationic and hydrophobic groups can be controlled independently by design in the ternary copolymers studied here.

Exploiting Macromolecular Design To Optimize the Antibacterial Activity of Alkylated Cationic Oligomers

There is growing interest in synthetic polymers which co-opt the structural features of naturally occurring antimicrobial peptides. However, our understanding of how macromolecular architecture affects antibacterial activity remains limited. To address this, we investigated whether varying architectures of a series of block and statistical co-oligomers influenced antibacterial and hemolytic activity. Cu(0)-mediated polymerization was used to synthesize oligomers constituting 2-(Boc-amino)ethyl acrylate units and either diethylene glycol ethyl ether acrylate (DEGEEA) or poly(ethylene glycol) methyl ether acrylate units with varying macromolecular architecture; subsequent deprotection produced primary amine functional oligomers. Further guanylation provided an additional series of antimicrobial candidates. Both chemical composition and macromolecular architecture were shown to affect antimicrobial activity. A broad spectrum antibacterial oligomer (containing guanidine moieties and DEGEEA units) was identified that possessed promising activity (MIC = 2 μg mL^-1) toward both Gram-negative and Gram-positive bacteria. Bacterial membrane permeabilization was identified as an important contributor to the mechanism of action.

Green Fabrication of Amphiphilic Quaternized β-Chitin Derivatives with Excellent Biocompatibility and Antibacterial Activities for Wound Healing

Bacterial infection has always been a great threat to public health, and new antimicrobials to combat it are urgently needed. Here, a series of quaternized β-chitin derivatives is prepared simply and homogeneously in an aqueous KOH/urea solution, which is a high-efficiency, energy-saving, and "green" route for the modification of chitin. The mild reaction conditions keep the acetamido groups of β-chitin intact and introduce quaternary ammonium groups on the primary hydroxyl at the C-6 position of the chitin backbone, allowing the quaternized β-chitin derivatives (QCs) to easily form micelles. These QCs are found to exhibit excellent antimicrobial activities against Escherichia coli, Staphylococcus aureus, Candida albicans, and Rhizopus oryzae with minimum inhibitory concentrations (MICs) of 8, 12, 60, and 40 µg mL-1 , respectively. As a specific highlight, their inherent outstanding biocompatibility and significant accelerating effects on the healing of uninfected, E. coli-infected, and S. aureus-infected wounds imply that these novel polysaccharide-based materials can be used as dressings for clinical skin regeneration, particularly for infected wounds.

Recent Progress in Polymer Research to Tackle Infections and Antimicrobial Resistance

Global health is increasingly being threatened by the rapid emergence of drug-resistant microbes. The ability of these microbes to form biofilms has further exacerbated the scenario leading to notorious infections that are almost impossible to treat. For addressing this clinical threat, various antimicrobial polymers, polymer-based antimicrobial hydrogels and polymer-coated antimicrobial surfaces have been developed in the recent past. This review aims to discuss such polymer-based antimicrobial strategies with a focus on their current advancement in the field. Antimicrobial polymers, whose designs are inspired from antimicrobial peptides (AMPs), are described with an emphasis on structure-activity analysis. Additionally, antibiofilm activity and in vivo efficacy are delineated to elucidate the real potential of these antimicrobial polymers as possible therapeutics. Antimicrobial hydrogels, prepared from either inherently antimicrobial polymers or biocide-loaded into polymer-derived hydrogel matrix, are elaborated followed by various strategies to engineer polymer-coated antimicrobial surfaces. In the end, the current challenges are accentuated along with future directions for further expansion of the field toward tackling infections and antimicrobial resistance.

Imidazolium and benzimidazolium-containing compounds: from simple toxic salts to highly bioactive drugs

The toxicity of simple imidazolium and benzimidazolium salts started to be more and more investigated in the last few years and was taken in consideration in the context of microorganisms, plants and more evolved organisms' exposure. However, the toxicity of these salts can be exploited in the development of different biological applications by incorporating them in the structure of compounds that specifically target microorganisms and cancer cells. We highlight in this minireview the way researchers became aware of the inherent problem of the stability and bioaccumulation of imidazolium and benzimidazolium salts and how they found inspiration to exploit their toxicity by incorporating them into new highly potent drugs.