Gold Nanoparticles with Antibiotic-Metallopolymers toward Broad-Spectrum Antibacterial Effects

Carboxymethyl chitosan stabilized AuNPs/ACP nanohybrids in enamel white spot lesions

Acidic bacterial biofilms-associated enamel white spot lesions (WSLs) are one of the hallmarks of early caries, causing demineralization and decomposition of dental hard tissues. Therefore, to effectively prevent and treat WSLs, it is important to inhibit the activity of cariogenic bacteria while promoting the remineralization of demineralized enamel. Amorphous calcium phosphate (ACP) favors hard tissue remineralization due to its biological activity and ability to release large amounts of Ca2+ and PO4 3-. However, ACP-based biomineralization technology is not effective due to its lack of antimicrobial properties. Here, carboxymethyl chitosan (CMCS) was employed as a reducing agent and stabilizer, and dual-functional nanohybrids CMCS/AuNPs/ACP with biofilm resistance and mineralization properties were successfully synthesized. The addition of AuNPs enhances the antimicrobial activity and participates in regulating the formation of hydroxyapatite (HAp). The nanohybrids exhibited significant destructive effects against cariogenic bacteria and their biofilms and showed bactericidal activity under bacteria-induced acidic conditions. More importantly, this nanohybrids showed superior results in promoting the remineralization of demineralized enamel, compared to fluoride and CMCS/ACP in vitro. The CMCS/AuNPs/ACP nanohybrids not only reverse the cariogenic microenvironment at the microbial level, but also promote self-repairing of enamel WSLs regarding the microstructure. The present work offers a theoretical and experimental basis for using the CMCS/AuNPs/ACP nanohybrids as a potential dual-functional agent for the clinical treatment of enamel WSLs.

Intrinsic antimicrobial resistance: Molecular biomaterials to combat microbial biofilms and bacterial persisters

The escalating rise in antimicrobial resistance (AMR) coupled with a declining arsenal of new antibiotics is imposing serious threats to global public health. A pervasive aspect of many acquired AMR infections is that the pathogenic microorganisms exist as biofilms, which are equipped with superior survival strategies. In addition, persistent and recalcitrant infections are seeded with bacterial persister cells at infection sites. Together, conventional antibiotic therapeutics often fail in the complete treatment of infections associated with bacterial persisters and biofilms. Novel therapeutics have been attempted to tackle AMR, biofilms, and persister-associated complex infections. This review focuses on the progress in designing molecular biomaterials and therapeutics to address acquired and intrinsic AMR, and the fundamental microbiology behind biofilms and persisters. Starting with a brief introduction of AMR basics and approaches to tackling acquired AMR, the emphasis is placed on various biomaterial approaches to combating intrinsic AMR, including (1) semi-synthetic antibiotics; (2) macromolecular or polymeric biomaterials mimicking antimicrobial peptides; (3) adjuvant effects in synergy; (4) nano-therapeutics; (5) nitric oxide-releasing antimicrobials; (6) antimicrobial hydrogels; (7) antimicrobial coatings. Particularly, the structure-activity relationship is elucidated in each category of these biomaterials. Finally, illuminating perspectives are provided for the future design of molecular biomaterials to bypass AMR and cure chronic multi-drug resistant (MDR) infections.

Gold nanoparticles exhibit anti-osteoarthritic effects via modulating interaction of the "microbiota-gut-joint" axis

Osteoarthritis (OA) is a common degenerative joint disease that can cause severe pain, motor dysfunction, and even disability. A growing body of research indicates that gut microbiota and their associated metabolites are key players in maintaining bone health and in the progression of OA. Short-chain fatty acids (SCFAs) are a series of active metabolites that widely participate in bone homeostasis. Gold nanoparticles (GNPs) with outstanding anti-bacterial and anti-inflammatory properties, have been demonstrated to ameliorate excessive bone loss during the progression of osteoporosis (OP) and rheumatoid arthritis (RA). However, the protective effects of GNPs on OA progression are not clear. Here, we observed that GNPs significantly alleviated anterior cruciate ligament transection (ACLT)-induced OA in a gut microbiota-dependent manner. 16S rDNA gene sequencing showed that GNPs changed gut microbial diversity and structure, which manifested as an increase in the abundance of Akkermansia and Lactobacillus. Additionally, GNPs increased levels of SCFAs (such as butyric acid), which could have improved bone destruction by reducing the inflammatory response. Notably, GNPs modulated the dynamic balance of M1/M2 macrophages, and increased the serum levels of anti-inflammatory cytokines such as IL-10. To sum up, our study indicated that GNPs exhibited anti-osteoarthritis effects via modulating the interaction of "microbiota-gut-joint" axis, which might provide promising therapeutic strategies for OA.

Antimicrobial Hydrogels: Potential Materials for Medical Application

Microbial infections based on drug-resistant pathogenic organisms following surgery or trauma and uncontrolled bleeding are the main causes of increased mortality from trauma worldwide. The prevalence of drug-resistant pathogens has led to a significant increase in medical costs and poses a great threat to the normal life of people. This is an important issue in the field of biomedicine, and the emergence of new antimicrobial materials hydrogels holds great promise for solving this problem. Hydrogel is an important material with good biocompatibility, water absorption, oxygen permeability, adhesion, degradation, self-healing, corrosion resistance, and controlled release of drugs as well as structural diversity. Bacteria-disturbing hydrogels have important applications in the direction of surgical treatment, wound dressing, medical device coating, and tissue engineering. This paper reviews the classification of antimicrobial hydrogels, the current status of research, and the potential of antimicrobial hydrogels for one application in biomedicine, and analyzes the current research of hydrogels in biomedical applications from five aspects: metal-loaded hydrogels, drug-loaded hydrogels, carbon-material-loaded hydrogels, hydrogels with fixed antimicrobial activity and biological antimicrobial hydrogels, and provides an outlook on the high antimicrobial activity, biodegradability, biocompatibility, injectability, clinical applicability and future development prospects of hydrogels in this field.

Metal-based nanoparticles in antibacterial application in biomedical field: Current development and potential mechanisms

The rise in drug resistance in pathogenic bacteria greatly endangers public health in the post-antibiotic era, and drug-resistant bacteria currently pose a great challenge not only to the community but also to clinical procedures, including surgery, stent implantation, organ transplantation, and other medical procedures involving any open wound and compromised human immunity. Biofilm-associated drug failure, as well as rapid resistance to last-resort antibiotics, necessitates the search for novel treatments against bacterial infection. In recent years, the flourishing development of nanotechnology has provided new insights for exploiting promising alternative therapeutics for drug-resistant bacteria. Metallic agents have been applied in antibacterial usage for several centuries, and the functional modification of metal-based biomaterials using nanotechnology has now attracted great interest in the antibacterial field, not only for their intrinsic antibacterial nature but also for their ready on-demand functionalization and enhanced interaction with bacteria, rendering them with good potential in further translation. However, the possible toxicity of MNPs to the host cells and tissue still hinders its application, and current knowledge on their interaction with cellular pathways is not enough. This review will focus on recent advances in developing metallic nanoparticles (MNPs), including silver, gold, copper, and other metallic nanoparticles, for antibacterial applications, and their potential mechanisms of interaction with pathogenic bacteria as well as hosts.

Study of bismuth metal organic skeleton composites with photocatalytic antibacterial activity

A composite based on Ag and carbon quantum dot (CQDs) doped bismuth metal organic framework (CAU-17) was synthesized by a one-step thermal solvent in situ growth. The microstructure, chemical composition, morphology, photogenerated electron-hole pairs, and photocatalytic activity of the composite were characterized. The produced composite with its unique energy band structure, enhances the visible light absorption and effectively delays the recombination of the photogenerated carriers. On the other hand, the modification with CQDs increases the concentration and transport rate of photogenerated carriers mainly attributed to their superior electron transport capacity and light trapping ability. The photocatalytic antibacterial effect of CAU-17/Ag/CQDs against common Gram-positive, Gram-negative bacteria (Staphylococcus aureus, Escherichia coli) and drug-resistant bacteria (methicillin-resistant Staphylococcus aureus), as well as its inhibition against HepG2 tumor cell were investigated. The results showed that CAU-17/Ag/CQDs exhibited a photocatalytic antibacterial effect with an inactivation rate as high as 99.9 %. At the low dose (0.2 mg/mL), CAU-17/Ag/CQDs indicated a significant inhibition against bacterial growth 20 min after visible light exposure, whereas at the concentration of 0.5 mg/mL, CAU-17/Ag/CQDs completely killed all the tested bacteria. At the concentration of 0.8 mg/mL, the inhibition rate against HepG2 tumor cells reached 75 %. The excellent photocatalytic property of the as prepared composite contributed to the doping of Ag and CQDs, which fundamentally altered the morphology and energy band distribution. Such a composite can be developed into an effective photocatalytic disinfection system and applied to water purification systems, biofilm rejection, combating different antibiotic resistances, and tumor therapy.

Membrane-Active Metallopolymers: Repurposing and Rehabilitating Antibiotics to Gram-Negative Superbugs

Among multiple approaches to combating antimicrobial resistance, a combination therapy of existing antibiotics with bacterial membrane-perturbing agents is promising. A viable platform of metallopolymers as adjuvants in combination with traditional antibiotics is reported in this work to combat both planktonic and stationary cells of Gram-negative superbugs and their biofilms. Antibacterial efficacy, toxicity, antibiofilm activity, bacterial resistance propensity, and mechanisms of action of metallopolymer-antibiotic combinations are investigated. These metallopolymers exhibit 4-16-fold potentiation of antibiotics against Gram-negative bacteria with negligible toxicity toward mammalian cells. More importantly, the lead combinations (polymer-ceftazidime and polymer-rifampicin) eradicate preformed biofilms of MDR E. coli and P. aeruginosa, respectively. Further, β-lactamase inhibition, outer membrane permeabilization, and membrane depolarization demonstrate synergy of these adjuvants with different antibiotics. Moreover, the membrane-active metallopolymers enable the antibiotics to circumvent bacterial resistance development. Altogether, the results indicate that such non-antibiotic adjuvants bear the promise to revitalize the efficacy of existing antibiotics to tackle Gram-negative bacterial infections.

Black Phosphorus - A Rising Star in the Antibacterial Materials

Antibiotics are the most commonly used means to treat bacterial infection at present, but the unreasonable use of antibiotics induces the generation of drug-resistant bacteria, which causes great problems for their clinical application. In recent years, researchers have found that nanomaterials with high specific surface area, special structure, photocatalytic activity and other properties show great potential in bacterial infection control. Among them, black phosphorus (BP), a two-dimensional (2D) nanomaterial, has been widely reported in the treatment of tumor and bone defect due to its excellent biocompatibility and degradability. However, the current theory about the antibacterial properties of BP is still insufficient, and the relevant mechanism of action needs to be further studied. In this paper, we introduced the structure and properties of BP, elaborated the mechanism of BP in bacterial infection, and systematically reviewed the application of BP composite materials in the field of antibacterial. At the same time, we also discussed the challenges faced by the current research and application of BP, which laid a solid theoretical foundation for the further study of BP in the future.

A potential strategy against clinical carbapenem-resistant Enterobacteriaceae: antimicrobial activity study of sweetener-decorated gold nanoparticles in vitro and in vivo

BACKGROUND

Carbapenem-resistant Enterobacteriaceae (CRE) present substantial challenges to clinical intervention, necessitating the formulation of novel antimicrobial strategies to counteract them. Nanomaterials offer a distinctive avenue for eradicating bacteria by employing mechanisms divergent from traditional antibiotic resistance pathways and exhibiting reduced susceptibility to drug resistance development. Non-caloric artificial sweeteners, commonly utilized in the food sector, such as saccharin, sucralose, acesulfame, and aspartame, possess structures amenable to nanomaterial formation. In this investigation, we synthesized gold nanoparticles decorated with non-caloric artificial sweeteners and evaluated their antimicrobial efficacy against clinical CRE strains.

RESULTS

Among these, gold nanoparticles decorated with aspartame (ASP_Au NPs) exhibited the most potent antimicrobial effect, displaying minimum inhibitory concentrations ranging from 4 to 16 µg/mL. As a result, ASP_Au NPs were chosen for further experimentation. Elucidation of the antimicrobial mechanism unveiled that ASP_Au NPs substantially elevated bacterial reactive oxygen species (ROS) levels, which dissipated upon ROS scavenger treatment, indicating ROS accumulation within bacteria as the fundamental antimicrobial modality. Furthermore, findings from membrane permeability assessments suggested that ASP_Au NPs may represent a secondary antimicrobial modality via enhancing inner membrane permeability. In addition, experiments involving crystal violet and confocal live/dead staining demonstrated effective suppression of bacterial biofilm formation by ASP_Au NPs. Moreover, ASP_Au NPs demonstrated notable efficacy in the treatment of Galleria mellonella bacterial infection and acute abdominal infection in mice, concurrently mitigating the organism's inflammatory response. Crucially, evaluation of in vivo safety and biocompatibility established that ASP_Au NPs exhibited negligible toxicity at bactericidal concentrations.

CONCLUSIONS

Our results demonstrated that ASP_Au NPs exhibit promise as innovative antimicrobial agents against clinical CRE.

Combatting resistance: Understanding multi-drug resistant pathogens in intensive care units

The escalating misuse and excessive utilization of antibiotics have led to the widespread dissemination of drug-resistant bacteria, posing a significant global healthcare crisis. Of particular concern is the increasing prevalence of multi-drug resistant (MDR) opportunistic pathogens in Intensive Care Units (ICUs), which presents a severe threat to public health and contributes to substantial morbidity and mortality. Among them, MDR ESKAPE pathogens account for the vast majority of these opportunistic pathogens. This comprehensive review provides a meticulous analysis of the current prevalence landscape of MDR opportunistic pathogens in ICUs, especially in ESKAPE pathogens, illuminating their resistance mechanisms against commonly employed first-line antibiotics, including polymyxins, carbapenems, and tigecycline. Furthermore, this review explores innovative strategies aimed at preventing and controlling the emergence and spread of resistance. By emphasizing the urgent need for robust measures to combat nosocomial infections caused by MDR opportunistic pathogens in ICUs, this study serves as an invaluable reference for future investigations in the field of antibiotic resistance.

Facially Amphiphilic Bile Acid-Functionalized Antimicrobials: Combating Pathogenic Bacteria, Fungi, and Their Biofilms

We report facially amphiphilic bile acid-based antimicrobials with a broad spectrum of activity against both bacterial and fungal pathogens and negligible detrimental effects on mammalian cells. Two lead compounds eliminated dormant subpopulations of various bacterial species, unlike conventional antibiotics. The lead compounds were also effective in eradicating biofilms of methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Candida albicans. Additionally, these compounds substantially inhibited the formation of fungal biofilms (C. albicans). Mechanistic investigations revealed the membrane-active nature and endogenous reactive oxygen species (ROS) induction ability of these compounds. Finally, no detectable resistance was developed by the bacterial strains against this class of membrane-targeting antimicrobials.

Ceftazidime-Decorated Gold Nanoparticles: a Promising Strategy against Clinical Ceftazidime-Avibactam-Resistant Enterobacteriaceae with Different Resistance Mechanisms

Nanoparticle-based antibiotic delivery systems are essential in combating antibiotic-resistant bacterial infections arising from acquired resistance and/or biofilm formation. Here, we report that the ceftazidime-decorated gold nanoparticles (CAZ_Au NPs) can effectively kill clinical ceftazidime-avibactam-resistant Enterobacteriaceae with various resistance mechanisms. Further study of underlying antibacterial mechanisms suggests that CAZ_Au NPs can damage the bacterial cell membrane and increase the level of intracellular reactive oxygen species. Moreover, CAZ_Au NPs show great potential in inhibiting biofilm formation and eradicating mature biofilms via crystal violet and scanning electron microscope assays. In addition, CAZ_Au NPs demonstrate excellent performance in improving the survival rate in the mouse model of abdominal infection. In addition, CAZ_Au NPs show no significant toxicity at bactericidal concentrations in the cell viability assay. Thus, this strategy provides a simple way to drastically improve the potency of ceftazidime as an antibiotic and its use in further biomedical applications.

The significance of metallic nanoparticles in the emerging, development and spread of antibiotic resistance

An ever-increasing number of newly synthesised nanoparticles have a constantly expanding range of applications. The large-scale implementation of nanoparticles will inevitably lead to intentional or accidental contamination of various environments. Since the major benefit of using several metallic nanoparticles is antimicrobial activity, these emerging contaminants may have a potentially hazardous impact on the development and spread of antibiotic resistance - a challenge that threats infection therapy worldwide. Few studies underline that metallic nanoparticles may affect the emergence and evolution of resistance via mutations and horizontal transfer between different bacterial species. Due to the complexity of factors and mechanisms involved in disseminating antibiotic resistance, it is crucial to investigate if metallic nanoparticles play a significant role in this process through co-selection ability and pressure exerted on bacteria. The aim of this review is to summarise the current research on mutations and three main horizontal gene transfer modes facilitated by nanoparticles. Here, the current results in the field are presented, major knowledge gaps and the necessity for more environmentally relevant studies are discussed.

The spread of antibiotic resistance to humans and potential protection strategies

Antibiotic resistance is currently one of the greatest threats to human health. Widespread use and residues of antibiotics in humans, animals, and the environment can exert selective pressure on antibiotic resistance bacteria (ARB) and antibiotic resistance gene (ARG), accelerating the flow of antibiotic resistance. As ARG spreads to the population, the burden of antibiotic resistance in humans increases, which may have potential health effects on people. Therefore, it is critical to mitigate the spread of antibiotic resistance to humans and reduce the load of antibiotic resistance in humans. This review briefly described the information of global antibiotic consumption information and national action plans (NAPs) to combat antibiotic resistance and provided a set of feasible control strategies for the transmission of ARB and ARG to humans in three areas including (a) Reducing the colonization capacity of exogenous ARB, (b) Enhancing human colonization resistance and mitigating the horizontal gene transfer (HGT) of ARG, (c) Reversing ARB antibiotic resistance. With the hope of achieving interdisciplinary one-health prevention and control of bacterial resistance.

Nanomaterials and nanomaterials-based drug delivery to promote cutaneous wound healing

Various factors could damage the structure and integrity of skin to cause wounds. Nonhealing or chronic wounds seriously affect the well-being of patients and bring heavy burdens to the society. The past few decades have witnessed application of numerous nanomaterials to promote wound healing. Owing to the unique physicochemical characteristics at nanoscale, nanomaterials-based therapy has been regarded as a potential approach to promote wound healing. In this review, we first overview the wound categories, wound healing process and critical influencing factors. Then applications of nanomaterials with intrinsic therapeutic effect and nanomaterials-based drug delivery systems to promote wound healing are addressed in detail. Finally, current limitations and future perspectives of nanomaterials in wound healing are discussed.

Nanotechnology: a contemporary therapeutic approach in combating infections from multidrug-resistant bacteria

In the 20th century, the discovery of antibiotics played an essential role in the fight against infectious diseases, including meningitis, typhoid fever, pneumonia and Mycobacterium tuberculosis. The development of multidrug resistance in microflora due to improper antibiotic use created significant public health issues. Antibiotic resistance has increased at an alarming rate in the past few decades. Multidrug-resistant bacteria (superbugs) such as methicillin-resistant Staphylococcus aureus (MRSA) as well as drug-resistant tuberculosis pose serious health implications. Despite the continuous increase in resistant microbes, the discovery of novel antibiotics is constrained by the cost and complexities of discovery of drugs. The nanotechnology has given new hope in combating this problem. In the present review, recent developments in therapeutics utilizing nanotechnology for novel antimicrobial drug development are discussed. The nanoparticles of silver, gold and zinc oxide have proved to be efficient antimicrobial agents against multidrug-resistant Klebsiella, Pseudomonas, Escherichia Coli and MRSA. Using nanostructures as carriers for antimicrobial agents provides better bioavailability, less chances of sub-therapeutic drug accumulation and less drug-related toxicity. Nanophotothermal therapy using fullerene and antibody functionalized nanostructures are other strategies that can prove to be helpful.

Deploying Gold Nanomaterials in Combating Multi-Drug-Resistant Bacteria

Antibiotic resistance has become a serious threat to human health due to the overuse of antibiotics. Different antibiotics are being developed to treat resistant bacteria, but the development cycle of antibiotics is hard to keep up with the high incidence of antibiotic resistance. Recent advances in antimicrobial nanomaterials have made nanotechnology a powerful solution to this dilemma. Among these nanomaterials, gold nanomaterials have excellent antibacterial efficacy and biosafety, making them alternatives to antibiotics. This review presents strategies that use gold nanomaterials to combat drug-resistant bacteria. We focus on the influence of physicochemical factors such as surface chemistry, size, and shape of gold nanomaterials on their antimicrobial properties and describe the antimicrobial applications of gold nanomaterials in medical devices. Finally, the existing challenges and future directions are discussed.

Metronidazole-loaded gold nanoparticles in natural rubber latex as a potential wound dressing

Gold nanoparticles (AuNPs) have shown interesting properties and specific biofunctions, providing benefits and new opportunities for controlled release systems. In this research, we demonstrated the use of natural rubber latex (NRL) from Hevea brasiliensis as a carrier of AuNPs and the antibiotic metronidazole (MET). We prepared AuNP-MET-NRL and characterized by physicochemical, biological and in vitro release assays. The effect of AuNPs on MET release was evaluated using UV-Vis and Laser-Induced Breakdown Spectroscopy (LIBS) techniques. AuNPs synthesized by Turkevich and Frens method resulted in a spherical shape with diameters of 34.8 ± 5.5 nm. We verified that there was no emergence or disappearance of new vibrational bands. Qualitatively and quantitatively, we showed that the MET crystals dispersed throughout the NRL. The Young's modulus and elongation values at dressing rupture were in the range appropriate for human skin application. 64.70% of the AuNP-MET complex was released within 100 h, exhibiting a second-order exponential release profile. The LIBS technique allowed monitoring of the AuNP release, indicating the Au emission peak reduction at 267.57 nm over time. Moreover, the dressing displayed an excellent hemocompatibility and fibroblast cell viability. These results demonstrated that the AuNP-MET-NRL wound dressing is a promising approach for dermal applications.

Nanomaterials-Based Combinatorial Therapy as a Strategy to Combat Antibiotic Resistance

Since the discovery of antibiotics, humanity has been able to cope with the battle against bacterial infections. However, the inappropriate use of antibiotics, the lack of innovation in therapeutic agents, and other factors have allowed the emergence of new bacterial strains resistant to multiple antibiotic treatments, causing a crisis in the health sector. Furthermore, the World Health Organization has listed a series of pathogens (ESKAPE group) that have acquired new and varied resistance to different antibiotics families. Therefore, the scientific community has prioritized designing and developing novel treatments to combat these ESKAPE pathogens and other emergent multidrug-resistant bacteria. One of the solutions is the use of combinatorial therapies. Combinatorial therapies seek to enhance the effects of individual treatments at lower doses, bringing the advantage of being, in most cases, much less harmful to patients. Among the new developments in combinatorial therapies, nanomaterials have gained significant interest. Some of the most promising nanotherapeutics include polymers, inorganic nanoparticles, and antimicrobial peptides due to their bactericidal and nanocarrier properties. Therefore, this review focuses on discussing the state-of-the-art of the most significant advances and concludes with a perspective on the future developments of nanotherapeutic combinatorial treatments that target bacterial infections.

Antimicrobial Activity Enhancers: Towards Smart Delivery of Antimicrobial Agents

The development of effective treatments against infectious diseases is an extensive and ongoing process due to the rapid adaptation of bacteria to antibiotic-based therapies. However, appropriately designed activity enhancers, including antibiotic delivery systems, can increase the effectiveness of current antibiotics, overcoming antimicrobial resistance and decreasing the chance of contributing to further bacterial resistance. The activity/delivery enhancers improve drug absorption, allow targeted antibiotic delivery, improve their tissue and biofilm penetration and reduce side effects. This review provides insights into various antibiotic activity enhancers, including polymer, lipid, and silver-based systems, designed to reduce the adverse effects of antibiotics and improve formulation stability and efficacy against multidrug-resistant bacteria.

Bridging micro/nano-platform and airway allergy intervention

Allergic airway diseases, with incidence augmenting visibly as industrial development and environmental degradation, are characterized by sneezing, itching, wheezing, chest tightness, airway obstruction, and hyperresponsiveness. Current medical modalities attempt to combat these symptoms mostly by small molecule chemotherapeutants, such as corticosteroids, antihistamines, etc., via intranasal approach which is one of the most noninvasive, rapid-absorbed, and patient-friendly routes. Nevertheless, inherent defects for irritation to respiratory mucosa, drug inactivation and degradation, and rapid drug dispersal to off-target sites are inevitable. Lately, intratracheal micro/nano therapeutic systems are emerging as innovative alternatives for airway allergy interventions. This overview introduces several potential application directions of mic/nano-platform in the treatment of airway allergic diseases, including carriers, therapeutic agents, and immunomodulators. The improvement of the existing drug therapy of respiratory allergy management by micro/nano-platform is described in detail. The challenges of the micro/nano-platform nasal approach in the treatment of airway allergy are summarized and the development of micro/nano-platform is also prospected. Although still a burgeoning area, micro/nano therapeutic systems are gradually turning to be realistic orientations as crucial future alternative therapeutic options in allergic airway inflammation interventions.

Biodegradable polycaprolactone metallopolymer-antibiotic bioconjugates containing phenylboronic acid and cobaltocenium for antimicrobial application

This paper reports antimicrobial metallopolymers containing biodegradable polycaprolactone as the backbone with boronic acid and cobaltocenium as the side chain. While boronic acid promotes interactions with bacterial cells via boronolectin with lipopolysaccharides, cationic cobaltocenium facilitates the unique complexation with anionic β-lactam antibiotics. The synergistic interactions in these metallopolymer-antibiotic bioconjugates were evidenced by re-sensitized efficacy of penicillin-G against four different Gram-negative bacteria (E. coli, P. vulgaris, P. aeruginosa and K. pneumoniae). The degradability of the polyester backbone was validated through tests under physiological pH (7.4) and acidic pH (5.5) or under enzymatic conditions. These metallopolymers exhibited time-dependent uptake and reduction of cobalt metals in different organs of mice via in vivo absorption, distribution, metabolism, and excretion (ADME) tests.

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

Co-Opting Host Receptors for Targeted Delivery of Bioconjugates-From Drugs to Bugs

Bioconjugation has allowed scientists to combine multiple functional elements into one biological or biochemical unit. This assembly can result in the production of constructs that are targeted to a specific site or cell type in order to enhance the response to, or activity of, the conjugated moiety. In the case of cancer treatments, selectively targeting chemotherapies to the cells of interest limit harmful side effects and enhance efficacy. Targeting through conjugation is also advantageous in delivering treatments to difficult-to-reach tissues, such as the brain or infections deep in the lung. Bacterial infections can be more selectively treated by conjugating antibiotics to microbe-specific entities; helping to avoid antibiotic resistance across commensal bacterial species. In the case of vaccine development, conjugation is used to enhance efficacy without compromising safety. In this work, we will review the previously mentioned areas in which bioconjugation has created new possibilities and advanced treatments.

Synthetic Antimicrobial Polymers in Combination Therapy: Tackling Antibiotic Resistance

Antibiotic resistance is a critical global healthcare issue that urgently needs new effective solutions. While small molecule antibiotics have been safeguarding us for nearly a century since the discovery of penicillin by Alexander Fleming, the emergence of a new class of antimicrobials in the form of synthetic antimicrobial polymers, which was driven by the advances in controlled polymerization techniques and the desire to mimic naturally occurring antimicrobial peptides, could play a key role in fighting multidrug resistant bacteria in the near future. By harnessing the ability to control chemical and structural properties of polymers almost at will, synthetic antimicrobial polymers can be strategically utilized in combination therapy with various antimicrobial coagents in different formats to yield more potent (synergistic) outcomes. In this review, we present a short summary of the different combination therapies involving synthetic antimicrobial polymers, focusing on their combinations with nitric oxide, antibiotics, essential oils, and metal- and carbon-based inorganics.

Smart nanomicelles with bacterial infection-responsive disassembly for selective antimicrobial applications

Electrostatic nanomicelles remain stable and biocompatible under physiological conditions, but readily burst and spill out cationic antimicrobial peptide to kill bacteria at infection sites.

NIR-responsive metal-containing polymer hydrogel for light-controlled microvalve

NIR-responsive metal-containing polymer hydrogel was prepared via the radical copolymerization of N-isopropylacrylamide and an osmium aromatic complex. It has excellent photothermal property and can be used as a light-controlled microvalve.

Emerging Strategies to Combat β-Lactamase Producing ESKAPE Pathogens

Since the discovery of penicillin by Alexander Fleming in 1929 as a therapeutic agent against staphylococci, β-lactam antibiotics (BLAs) remained the most successful antibiotic classes against the majority of bacterial strains, reaching a percentage of 65% of all medical prescriptions. Unfortunately, the emergence and diversification of β-lactamases pose indefinite health issues, limiting the clinical effectiveness of all current BLAs. One solution is to develop β-lactamase inhibitors (BLIs) capable of restoring the activity of β-lactam drugs. In this review, we will briefly present the older and new BLAs classes, their mechanisms of action, and an update of the BLIs capable of restoring the activity of β-lactam drugs against ESKAPE (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens. Subsequently, we will discuss several promising alternative approaches such as bacteriophages, antimicrobial peptides, nanoparticles, CRISPR (clustered regularly interspaced short palindromic repeats) cas technology, or vaccination developed to limit antimicrobial resistance in this endless fight against Gram-negative pathogens.

The Demand for New Antibiotics: Antimicrobial Peptides, Nanoparticles, and Combinatorial Therapies as Future Strategies in Antibacterial Agent Design

The inappropriate use of antibiotics and an inadequate control of infections have led to the emergence of resistant strains which represent a major threat to public health and the global economy. Therefore, research and development of a new generation of antimicrobials to mitigate the spread of antibiotic resistance has become imperative. Current research and technology developments have promoted the improvement of antimicrobial agents that can selectively interact with a target site (e.g., a gene or a cellular process) or a specific pathogen. Antimicrobial peptides and metal nanoparticles exemplify a novel approach to treat infectious diseases. Nonetheless, combinatorial treatments have been recently considered as an excellent platform to design and develop the next generation of antibacterial agents. The combination of different drugs offers many advantages over their use as individual chemical moieties; these include a reduction in dosage of the individual drugs, fewer side effects compared to the monotherapy, reduced risk for the development of drug resistance, a better combined response compared to the effect of the individual drugs (synergistic effects), wide-spectrum antibacterial action, and the ability to attack simultaneously multiple target sites, in many occasions leading to an increased antibacterial effect. The selection of the appropriate combinatorial treatment is critical for the successful treatment of infections. Therefore, the design of combinatorial treatments provides a pathway to develop antimicrobial therapeutics with broad-spectrum antibacterial action, bactericidal instead of bacteriostatic mechanisms of action, and better efficacy against multidrug-resistant bacteria.

Small Molecules with Membrane-Active Antibacterial Activity

This spotlight on application provides a brief overview of our research exploration, focusing on the research of small molecules with membrane-active antibacterial activity that mimic host-defense peptides (HDPs). The development of antimicrobial HDP agents is an emerging research area as they circumvent the potential disadvantages of HDPs. The small molecules are preferable for development due to their low production cost and potential of more practical applications. In recent years, we conducted research on the design of antibacterial agents based on small molecules including hydantoins, acylated reduced amides, biscyclic guanidines, and dimeric alkylamides of lysines. We herein sketch our journey on the exploration of the antimicrobial activity of these few classes of molecules and hopefully share our insight in the future design of small-molecular-weight antibiotic agents with membrane-active activity that mimic HDPs.

Facial Amphiphilicity-Induced Polymer Nanostructures for Antimicrobial Applications

New antimicrobial agents are needed to address ever-increasing antimicrobial resistance and a growing epidemic of infections caused by multidrug resistant pathogens. We design nanostructured antimicrobial copolymers containing multicyclic natural products that bear facial amphiphilicity. Bile acid based macromolecular architectures of these nanostructures can interact preferentially with bacterial membranes. Incorporation of polyethylene glycol into the copolymers not only improved the colloidal stability of nanostructures but also increased the biocompatibility. This study investigated the effects of facial amphiphilicity, polymer architectures, and self-assembled nanostructures on antimicrobial activity. Advanced nanostructures such as spheres, vesicles, and rod-shaped aggregates are formed in water from the facial amphiphilic cationic copolymers via supramolecular interactions. These aggregates were particularly interactive toward Gram-positive and Gram-negative bacterial cell membranes and showed low hemolysis against mammalian cells.

Metallo-Polyelectrolytes: Correlating Macromolecular Architectures with Properties and Applications

Since the middle of the 20th century, metallopolymers have represented a standalone subfield with a beneficial combination of functionality from inorganic metal centers and processability from the organic polymeric frameworks. Metallo-polyelectrolytes are a new class of soft materials that showcase fundamentally different properties from neutral polymers due to their intrinsically ionic behaviors. This review describes recent trends in metallo-polyelectrolytes and discusses emerging properties and challenges, as well as future directions from a perspective of macromolecular architectures. The correlations between macromolecular architectures and properties are discussed from copolymer self-assembly, metallo-enzymes for biomedical applications, metallo-peptides for catalysis, crosslinked networks, and metallogels.

Polymerization-Induced Self-Assembly of Metallo-Polyelectrolyte Block Copolymers

Cobaltocenium-containing polyelectrolyte block copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using aqueous dispersion RAFT polymerization. The cationic steric stabilizer was a macromolecular chain-transfer agent (macro-CTA) based on poly (2-cobaltocenium amidoethyl methacrylate chloride) (PCoAEMACl), and the core-forming block was poly(2-hydroxypropyl methacrylate) (PHPMA). Stable cationic spherical nanoparticles were formed in aqueous solution with low dispersity without adding any salts. The chain extension of macro-CTA with HPMA was efficient and fast. The effects of block copolymer compositions, solid content, charge density, and addition of salts were studied. It was found that the degree of polymerization of both the stabilizer PCoAEMACl and the core-forming PHPMA had a strong influence on the size of nanoparticles.

Optimization of Antibacterial Efficacy of Noble-Metal-Based Core-Shell Nanostructures and Effect of Natural Organic Matter

Noble-metal-based nanomaterials made of less toxic metals have been utilized as potential antibacterial agents due to their distinctive oxidase-like activity. In this study, we fabricated core-shell structured Pd@Ir bimetallic nanomaterials with an ultrathin shell. Pd@Ir nanostructures show morphology-dependent bactericidal activity, in which Pd@Ir octahedra possessing higher oxidase-like activity exert bactericidal activity stronger than that of Pd@Ir cubes. Furthermore, our results reveal that the presence of natural organic matter influences the antibacterial behaviors of nanomaterials. Upon interaction with humic acid (HA), the Pd@Ir nanostructures induce an elevated level of reactive oxygen species, resulting in significantly enhanced bactericidal activity of the nanostructures. Mechanism analysis shows that the presence of HA efficiently enhances the oxidase-like activity of nanomaterials and promotes the cellular internalization of nanomaterials. We believe that the present study will not only demonstrate an effective strategy for improving the bactericidal activity of noble-metal-based nanomaterials but also provide an understanding of the antibacterial behavior of nanomaterials in the natural environment.

Nanomaterials as Delivery Vehicles and Components of New Strategies to Combat Bacterial Infections: Advantages and Limitations

Life-threatening bacterial infections have been well-controlled by antibiotic therapies and this approach has greatly improved the health and lifespan of human beings. However, the rapid and worldwide emergence of multidrug resistant (MDR) bacteria has forced researchers to find alternative treatments for MDR infections as MDR bacteria can sometimes resist all the present day antibiotic therapies. In this respect, nanomaterials have emerged as innovative antimicrobial agents that can be a potential solution against MDR bacteria. The present review discusses the advantages of nanomaterials as potential medical means and carriers of antibacterial activity, the types of nanomaterials used for antibacterial agents, strategies to tackle toxicity of nanomaterials for clinical applications, and limitations which need extensive studies to overcome. The current progress of using different types of nanomaterials, including new emerging strategies for the single purpose of combating bacterial infections, is also discussed in detail.

Gold Nanoparticles Cure Bacterial Infection with Benefit to Intestinal Microflora

Antibiotics that are most used to cure bacterial infections in the clinic result in the imbalance of intestinal microflora, destroy the intestinal barrier, and induce bacterial resistance. There is an urgent need for antibacterial agent therapy for bacterial infections that does not destroy intestinal microflora. Herein, we applied 4,6-diamino-2-pyrimidinethiol (DAPT)-coated Au nanoparticles (D-Au NPs) for therapy of bacterial infection induced by Escherichia coli ( E. coli) in the gut. We cultured D-Au NPs and E. coli in an anaerobic atmosphere to evaluate their bactericidal effect. We studied the microflora, distribution of Au, and biomarkers in mice after a 28-day oral administration to analyze the effect of Au NPs on mice. D-Au NPs cured bacterial infections more effectively than levofloxacin without harming intestinal microflora. D-Au NPs showed great potential as alternatives to oral antibiotics.