A lack of drugs for antibiotic-resistant Gram-negative bacteria

An effective approach to obtain functional poly-β-peptides for combating drug-resistant bacterial infections

The high mortality of drug-resistant bacterial infections, especially those caused by multidrug-resistant Gram-negative pathogens, highlights an urgent demand for promising antimicrobial strategies. Host defense peptide (HDP)-mimicking poly-β-peptides have demonstrated significant potential in combating drug-resistant bacterial infections, with their antimicrobial activity closely dependent on their side-chain structures. However, the restricted structural diversity of poly-β-peptides necessitates efficient synthetic methods to expand their diversity, particularly positively charged side-chain structures. This study presents a water-tolerant approach that facilitates the controllable synthesis of poly-β-peptides with different chain lengths and structurally diverse side chains, including primary amines, tertiary amines, as well as alkyl, aryl, and methoxy groups. This approach serves as an HDP-mimicking discovery platform to obtain the optimal poly-β-peptide, AOc0.8HNL0.2, which exhibits broad-spectrum antibacterial activity and high selectivity against drug-resistant bacteria. The antibacterial mechanism studies reveal that AOc0.8HNL0.2 disrupts the membrane of Gram-negative bacteria. In vivo evaluations substantiate the therapeutic potential of AOc0.8HNL0.2 in treating drug-resistant bacterial infections with no observable toxicity. This study underscores the potential of this convenient synthetic strategy as a promising platform for developing antimicrobial poly-β-peptides to combat the growing threat of drug-resistant bacterial infections.

Carbon-TiO2 Hybrid Quantum Dots for Photocatalytic Inactivation of Gram-Positive and Gram-Negative Bacteria

Carbon-semiconductor hybrid quantum dots are classical carbon dots with core carbon nanoparticles doped with a selected nanoscale semiconductor. Specifically, on those with the nanoscale TiO2 doping, denoted as CTiO2-Dots, their synthesis and thorough characterization were reported previously. In this work, the CTiO2-Dots were evaluated for their visible light-activated antibacterial function, with the results showing the effective killing of not only Gram-positive but also the generally more resistant Gram-negative bacteria. The hybrid dots are clearly more potent antibacterial agents than their neat carbon dot counterparts. Mechanistically, the higher antibacterial performance of the CTiO2-Dots is attributed to their superior photoexcited state properties, which are reflected by the observed much brighter fluorescence emissions. Also considered and discussed is the possibility of additional contributions to the antibacterial activities due to the photosensitization of the nanoscale TiO2 by its doped core carbon nanoparticles.

Capsule Shedding and Membrane Binding Enhanced Photodynamic Killing of Gram-Negative Bacteria by a Unimolecular Conjugated Polyelectrolyte

The development of new antimicrobial agents to treat infections caused by Gram-negative bacteria is of paramount importance due to increased antibiotic resistance worldwide. Herein, we show that a water-soluble porphyrin-cored hyperbranched conjugated polyelectrolyte (PorHP) exhibits high photodynamic bactericidal activity against the Gram-negative bacteria tested, including a multidrug-resistant (MDR) pathogen, while demonstrating low cytotoxicity toward mammalian cells. Comprehensive analyses reveal that the antimicrobial activity of PorHP proceeds via a multimodal mechanism by effective bacterial capsule shedding, strong bacterial outer membrane binding, and singlet oxygen generation. Through this multimodal antimicrobial mechanism, PorHP displays significant performance for Gram-negative bacteria with >99.9% photodynamic killing efficacy. Overall, PorHP shows great potential as an antimicrobial agent in fighting the growing threat of Gram-negative bacteria.

Bio-inspired peptide-conjugated liposomes for enhanced planktonic bacteria killing and biofilm eradication

Developing new antimicrobial agents has become an urgent task to address the increasing prevalence of multidrug-resistant pathogens and the emergence of biofilms. Cationic antimicrobial peptides (AMPs) have been regarded as promising candidates due to their unique non-specific membrane rupture mechanism. However, a series of problems with the peptides hindered their practical application due to their high toxicity and low bioactivity and stability. Here, inspired by broadening the application of cell-penetrating peptides (CPPs), we selected five different sequences of cationic peptides which are considered as both CPPs and AMPs, and developed a biomimetic strategy to construct cationic peptide-conjugated liposomes with the virus-like structure for both enhancements of antibacterial efficacy and biosafety. The correlation between available peptide density/peptide variety and antimicrobial capabilities was evaluated from quantitative perspectives. Computational simulation and experimental investigations assisted to identify the optimal peptide-conjugated liposomes and revealed that the designed system provides high charge density for enhanced anionic bacterial membrane binding capability without compromised cytotoxicity, being capable of enhanced antibacterial efficacy of bacteria/biofilm of clinically important pathogens. The bio-inspired design has shown enhanced therapeutic efficiency of peptides and may promote the development of next-generation antimicrobials.

Engineering Self-Assembled Endolysin Nanoparticles against Antibiotic-Resistant Bacteria

Antibiotic resistance represents a serious global health concern and has stimulated the development of antimicrobial nanomaterials to combat resistant bacteria. Protein-based nanoparticles combining characteristics of both proteins and nanoparticles offer advantages including high biocompatibility, attractive biodegradability, enhanced bioavailability and functional versatility. They have played an increasing role as promising candidates for broad applications ranging from biocatalysts and drug delivery to vaccine development to cancer therapeutics. However, their application as antibacterial biomaterials to address challenging antibiotic-resistance problems has not been explicitly pursued. Herein, we describe engineering protein-only nanoparticles against resistant Gram-positive bacteria. A self-assembling peptide (P114) enables the assembly of a phage lytic enzyme (P128) into nanoparticles in response to pH reduction. Compared to native P128 and monomeric P114-P128, P128 nanoparticles (P128NANO) demonstrated a stronger bactericidal ability with high potency at lower concentrations (2-3-fold lower), particularly for methicillin-resistant Staphylococcus aureus strains. In addition, P128NANO showed an enhanced thermal (up to 65 °C) and storage stability and elicited extensive damages to bacterial cell walls. These remarkable antibacterial abilities are likely due to the P128NANO nanostructure, mediating multivalent interactions with bacterial cell walls at increased local concentrations of endolysin. The engineered endolysin nanoparticles offer a promising antimicrobial alternative to conventional antibiotics.

Propolis efficacy on SARS-COV viruses: a review on antimicrobial activities and molecular simulations

This current study review provides a brief review of a natural bee product known as propolis and its relevance toward combating SARS-CoV viruses. Propolis has been utilized in medicinal products for centuries due to its excellent biological properties. These include anti-oxidant, immunomodulatory, anti-inflammatory, anti-viral, anti-fungal, and bactericidal activities. Furthermore, studies on molecular simulations show that flavonoids in propolis may reduce viral replication. While further research is needed to validate this theory, it has been observed that COVID-19 patients receiving propolis show earlier viral clearance, enhanced symptom recovery, quicker discharge from hospitals, and a reduced mortality rate relative to other patients. As a result, it appears that propolis could probably be useful in the treatment of SARS-CoV-2-infected patients. Therefore, this review sought to explore the natural properties of propolis and further evaluated past studies that investigated propolis as an alternative product for the treatment of COVID-19 symptoms. In addition, the review also highlights the possible mode of propolis action as well as molecular simulations of propolis compounds that may interact with the SARS-CoV-2 virus. The activity of propolis compounds in decreasing the impact of COVID-19-related comorbidities, the possible roles of such compounds as COVID-19 vaccine adjuvants, and the use of nutraceuticals in COVID-19 treatment, instead of pharmaceuticals, has also been discussed.

Visualization of Antimicrobial-Induced Bacterial Membrane Disruption with a Bicolor AIEgen

Gram-negative bacteria are difficult to kill due to their complex cell envelope, including the outer membrane (OM) and cytoplasmic membrane (CM). To monitor the membranolytic action of antimicrobials on Gram-negative bacteria would facilitate the development of effective antimicrobials. In this paper, an aggregation-induced emission luminogen (AIEgen) with microenvironment-sensitive properties was employed to indicate the interaction of antimicrobials with the OM and CM of Gram-negative bacteria. The damaged extent of OM and CM caused by antimicrobials with the change of dosage and incubation time can be visually captured based on the variation of two emission colors of IQ-Cm responding to OM-defective (green) and CM-disruptive bacteria (orange). Meanwhile, the activity assessment of antimicrobials can be easily realized within 1~2 h based on the distinct response of IQ-Cm to live and dead E. coli, which is much faster than the agar plate culture. This probe may shed light on the understanding of the interaction between the membrane-active antimicrobials and cell envelope of Gram-negative bacteria and contribute to the future development of antimicrobials.

Host defense peptide mimicking cyclic peptoid polymers exerting strong activity against drug-resistant bacteria

Extensive use of antibiotics accelerates the emergence of drug-resistant bacteria and related infections. Host defense peptides (HDPs) have been studied as promising and potential therapeutic candidates. However, their clinical applications of HDPs are limited due to their high cost of synthesis and low stability upon proteolysis. Therefore, HDP mimics have become a new approach to address the challenge of bacterial resistance. In this work, we design the amphiphilic peptoid polymers by mimicking the positively charged and hydrophobic structures of HDPs and synthesize a series of cyclic peptoid polymers efficiently via the polymerization on α-amino acid N-substituted glycine N-carboxyanhydrides (α-NNCAs) using 1,8-diazabicycloundec-7-ene (DBU) as the initiator. The optimal cyclic peptoid polymer, poly(Naeg_0.7Npfbg_0.3)₂₀, displays strong antibacterial activities against drug-resistant bacteria, but low hemolysis and cytotoxicity. In addition, the mode-of-action study indicates that the antibacterial mechanism is associated with bacterial membrane interaction. Our study implies that HDP mimicking cyclic peptoid polymers have potential application in treating drug-resistant bacterial infections.

Biomaterial-based delivery of antimicrobial therapies for the treatment of bacterial infections

The rise in antibiotic-resistant bacteria, including strains that are resistant to last-resort antibiotics, and the limited ability of antibiotics to eradicate biofilms, have necessitated the development of alternative antibacterial therapeutics. Antibacterial biomaterials, such as polycationic polymers, and biomaterial-assisted delivery of non-antibiotic therapeutics, such as bacteriophages, antimicrobial peptides and antimicrobial enzymes, have improved our ability to treat antibiotic-resistant and recurring infections. Biomaterials not only allow targeted delivery of multiple agents, but also sustained release at the infection site, thereby reducing potential systemic adverse effects. In this Review, we discuss biomaterial-based non-antibiotic antibacterial therapies for the treatment of community- and hospital-acquired infectious diseases, with a focus in in vivo results. We highlight the translational potential of different biomaterial-based strategies, and provide a perspective on the challenges associated with their clinical translation. Finally, we discuss the future scope of biomaterial-assisted antibacterial therapies.

WEB SUMMARY

The development of antibiotic tolerance and resistance has demanded the search for alternative antibacterial therapies. This Review discusses antibacterial biomaterials and biomaterial-assisted delivery of non-antibiotic therapeutics for the treatment of bacterial infectious diseases, with a focus on clinical translation.

Synthesis and evaluation of an amphiphilic deferoxamine:gallium-conjugated cationic random copolymer against a murine wound healing infection model of Pseudomonas aeruginosa

Multidrug resistant (MDR) Gram-negative bacteria are an urgent global health threat. We report on the design and evaluation of a xenosiderophore-conjugated cationic random copolymer (pGQ-DG) which exhibits selective antibacterial activity against Pseudomonas aeruginosa (P. aeruginosa) by targeting select outer membrane (OM) receptors for scavenging xenosiderophores such as deferoxamine (DFO), while possessing favorable cytocompatibility and exhibiting low hemolysis, to enhance and safely damage the bacterial OM. pGQ-DG demonstrated synergistic properties in combination with vancomycin (VAN) when evaluated in vitro against P. aeruginosa. In addition, pGQ-DG plus VAN cleared the P. aeruginosa infection and efficiently accelerated healing in a murine wound healing model as effectively as colistin, suggesting that this strategy could serve as an alternative to colistin against MDR bacteria. STATEMENT OF SIGNIFICANCE: P. aeruginosa exhibits intrinsic antibiotic resistance due to limited permeability of its outer membrane (OM). A triple combination antipseudomonal approach was investigated by 1) selectively targeting P. aeruginosa through the complex DFO:gallium, 2) disrupting the OM through a cationic random copolymer, and 3) enhancing bacteria sensitivity to VAN as a result of the OM disruption. Synthesis and characterization of the lead polymer pGQ-DG, mechanism of action, antimicrobial activity, and biocompatibility were investigated in vitro and in vivo. Overall pGQ-DG plus VAN cleared the P. aeruginosa infection and accelerated wound healing in mice as effectively as colistin, suggesting that this strategy could serve as an alternative to colistin against multidrug resistant P. aeruginosa.

Epidemiology of bloodstream infections in a Scottish haemodialysis population with focus on vascular access method

BACKGROUND

Infection is the second highest cause of mortality in end-stage renal disease, with a significant proportion relating to haemodialysis (HD) vascular access-related infection (VARI).

AIM

To report the rate and antimicrobial resistance (AMR) of all-source bloodstream infections (BSIs) by vascular access type in a Scottish HD cohort.

METHODS

Retrospective analysis was undertaken of data on adult patients attending seven HD units during 2017. Total HD days for each vascular access type were calculated. BSIs were analysed with rates expressed per 1000 HD days. AMR was verified using health board microbiology databases.

FINDINGS

Excluding contaminant organisms, there was an overall BSI rate of 0.57 per 1000 HD days. The highest all-source and vascular access-related infection (VARI) BSI rates per 1000 HD days were in the non-tunnelled central venous catheter (CVC) group (3.11 and 2.07 respectively), followed by tunnelled CVC (1.10 and 0.67), arteriovenous graft (0.51 and 0.31), and finally arteriovenous fistula (0.29 and 0.02). The non-VARI BSI rates were lowest in the arteriovenous graft group. Staphylococci comprised the majority of events, with Staphylococcus aureus implicated in 29%. Gram-negative BSIs were prevalent, particularly in CVC groups, and associated with higher mortality. Multidrug-resistant (MDR) S. aureus and carbapenem resistance were relatively low. MDR Gram-negatives were high compared with the Scottish population.

CONCLUSION

Arteriovenous fistula access is confirmed as having lowest all-source and VARI BSI rates, and arteriovenous graft access the lowest non-VARI BSI rates. Staphylococci remain the prevailing genus; however, the contributions of Gram-negative BSIs, the higher mortality, and proportion of MDR organisms in this group are notable.

Multiple action mechanism and in vivo antimicrobial efficacy of antimicrobial peptide Jelleine-I

With the extensive use of antibiotics in medicine, agriculture and food chemistry, the emergence of multi-drug resistant bacteria become more and more frequent and posed great threats to human health and life. So novel antimicrobial agents were urgently needed to defend the resistant bacteria. Jelleine-I was a small antimicrobial peptide (AMP) with eight amino acids in its sequence. It was believed to be an ideal template for developing antimicrobial agents. In the present study, the possible action mode against both gram-negative bacteria and gram-positive bacteria and in vivo antimicrobial activity was explored. Our results showed that Jelleine-I exhibits its antimicrobial activity mainly by disrupting the integrity of the cell membrane, which would not be affected by the conventional resistant mechanism. It also aims at some intracellular targets such as genomic DNA to inhibit the growth of microbes. In addition, the result of in vivo antimicrobial activity experiment showed that Jelleine-I performed a good therapeutic effect toward the mice with Escherichia coli infected peritonitis. Notably, Jelleine-I has negligible cytotoxicity toward the tested mammalian cells, indicating excellent cell selectivity between prokaryotic cells and eurkayotic cells. In summary, our results showed that Jelleine-I would be a potential candidate to be developed as a novel antimicrobial agent.

Highlights in Mesoporous Silica Nanoparticles as a Multifunctional Controlled Drug Delivery Nanoplatform for Infectious Diseases Treatment

Infectious diseases are a major global concern being responsible for high morbidity and mortality mainly due to the development and enhancement of multidrug-resistant microorganisms exposing the fragility of medicines and vaccines commonly used to these treatments. Taking into account the scarcity of effective formulation to treat infectious diseases, nanotechnology offers a vast possibility of ground-breaking platforms to design new treatment through smart nanostructures for drug delivery purposes. Among the available nanosystems, mesoporous silica nanoparticles (MSNs) stand out due their multifunctionality, biocompatibility and tunable properties make them emerging and actual nanocarriers for specific and controlled drug release. Considering the high demand for diseases prevention and treatment, this review exploits the MSNs fabrication and their behavior in biological media besides highlighting the most of strategies to explore the wide MSNs functionality as engineered, smart and effective controlled drug release nanovehicles for infectious diseases treatment. Graphical Abstract Schematic representation of multifunctional MSNs-based nanoplatforms for infectious diseases treatment.

Cationic Peptidopolysaccharide with an Intrinsic AIE Effect for Combating Bacteria and Multicolor Imaging

An antibacterial polymer peptidopolysaccharide (COS-AMP) that integrates antibacterial and detection functions is constructed with a simple synthetic method. The COS-AMP is constructed by simulating the structure of peptidoglycan of the bacterial cell wall with chitooligosaccharide with intrinsic aggregation-induced emission (AIE) effect as the main chain, as well as a peptide polymer grafted onto its amino group. Based on the AIE effect and excitation-dependent fluorescence of COS-AMP, it is tentatively applied to multicolor imaging and quantification of bacteria. This multicolor imaging helps to match different excitation sources of fluorescent instrument for straightforward imaging and detection. The structural similarity with the bacterial cell wall component facilitates the passage of COS-AMP across the cell wall and destroys the bacterial structure, thus it has a good broad-spectrum antibacterial activity. In addition, aromatic fluorophores are not needed, and excellent biocompatibility will make it have broad application prospects.

Short, symmetric-helical peptides have narrow-spectrum activity with low resistance potential and high selectivity

Broad-spectrum antibiotics have, until now, been the mainstay of antibiotic therapy. However, the increasing threat of drug-resistant bacteria and the ecological imbalance of normal microbial communities have forced a reconsideration of the best strategies to treat such pathogens. Therefore, antibacterial agents with specific abilities of eliminating pathogens may provide long-term protection. Antimicrobial peptides (AMPs), which can be optimized by modifying their primary sequences, are regarded as potentially valuable in development of pathogen-specific agents. To obtain efficient narrow-spectrum AMPs, database-filtering technology, which filters the most probable amino acid composition, positive charge, sequence length and hydrophobic content of peptides against Gram-negative bacteria, was taken as the first step. Then, the filtered parameters were distributed and modified into an α-helical symmetrical structure by considering the structure-function relationship of synthesized antimicrobial peptides. Finally, short, safe and stable peptides against Escherichia coli, Salmonella pullorum and Pseudomonas aeruginosa were successfully identified. The potential peptides F1 and F4 showed low cell toxicity, low resistance potential and low salt sensitivity. CD spectroscopy of the peptides illustrated that F1 and F4 exhibited a tendency towards an α-helical structure in a membrane-mimetic environment. Indeed, fluorescence spectroscopy and electron microscopy analyses indicated that the shorter potential sequence F4 killed the bacteria by causing physical destruction of the bacterial membrane and cytosol leakage. In the mouse model test, F4 reduced the bacterial load in major organs and the cytokine (TNF-α, IL-6, and IL-1β) levels in serum significantly (P < 0.05). Collectively, this symmetric-helical distribution, dependent on database-filtering parameters, is a promising strategy for designing effective smart AMPs with high cell selectivity, and it also provides new insights into the design and optimization of pathogen-specific biomaterials.

Design of stapled antimicrobial peptides that are stable, nontoxic and kill antibiotic-resistant bacteria in mice

The clinical translation of cationic α-helical antimicrobial peptides (AMPs) has been hindered by structural instability, proteolytic degradation and in vivo toxicity from nonspecific membrane lysis. Although analyses of hydrophobic content and charge distribution have informed the design of synthetic AMPs with increased potency and reduced in vitro hemolysis, nonspecific membrane toxicity in vivo continues to impede AMP drug development. Here, we analyzed a 58-member library of stapled AMPs (StAMPs) based on magainin II and applied the insights from structure-function-toxicity measurements to devise an algorithm for the design of stable, protease-resistant, potent and nontoxic StAMP prototypes. We show that a lead double-stapled StAMP named Mag(i+4)1,15(A9K,B21A,N22K,S23K) can kill multidrug-resistant Gram-negative pathogens, such as colistin-resistant Acinetobacter baumannii in a mouse peritonitis-sepsis model, without observed hemolysis or renal injury in murine toxicity studies. Inputting the amino acid sequences alone, we further generated membrane-selective StAMPs of pleurocidin, CAP18 and esculentin, highlighting the generalizability of our design platform.

Pathogen-Specific Polymeric Antimicrobials with Significant Membrane Disruption and Enhanced Photodynamic Damage To Inhibit Highly Opportunistic Bacteria

Highly pathogenic Gram-negative bacteria and their drug resistance are a severe public health threat with high mortality. Gram-negative bacteria are hard to kill due to the complex cell envelopes with low permeability and extra defense mechanisms. It is challenging to treat them with current strategies, mainly including antibiotics, peptides, polymers, and some hybrid materials, which still face the issue of drug resistance, limited antibacterial selectivity, and severe side effects. Together with precise bacteria targeting, synergistic therapeutic modalities, including physical membrane damage and photodynamic eradication, are promising to combat Gram-negative bacteria. Herein, pathogen-specific polymeric antimicrobials were formulated from amphiphilic block copolymers, poly(butyl methacrylate)- b-poly(2-(dimethylamino) ethyl methacrylate- co-eosin)- b-ubiquicidin, PBMA- b-P(DMAEMA- co-EoS)-UBI, in which pathogen-targeting peptide ubiquicidin (UBI) was tethered in the hydrophilic chain terminal, and Eosin-Y was copolymerized in the hydrophilic block. The micelles could selectively adhere to bacteria instead of mammalian cells, inserting into the bacteria membrane to induce physical membrane damage and out-diffusion of intracellular milieu. Furthermore, significant in situ generation of reactive oxygen species was observed upon light irradiation, achieving further photodynamic eradication. Broad-spectrum bacterial inhibition was demonstrated for the polymeric antimicrobials, especially highly opportunistic Gram-negative bacteria, such as Pseudomona aeruginosa ( P. aeruginosa) based on the synergy of physical destruction and photodynamic therapy, without detectable resistance. In vivo P. aeruginosa-infected knife injury model and burn model both proved good potency of bacteria eradication and promoted wound healing, which was comparable with commercial antibiotics, yet no risk of drug resistance. It is promising to hurdle the infection and resistance suffered from highly opportunistic bacteria.

Mixed-charge pseudo-zwitterionic mesoporous silica nanoparticles with low-fouling and reduced cell uptake properties

The design of drug delivery systems needs to consider biocompatibility and host body recognition for an adequate actuation. In this work, mesoporous silica nanoparticles (MSNs) surfaces were successfully modified with two silane molecules to provide mixed-charge brushes (-NH3⊕/-PO3⊝) and well evaluated in terms of surface properties, low-fouling capability and cell uptake in comparison to PEGylated MSNs. The modification process consists in the simultaneous direct-grafting of hydrolysable short chain amino (aminopropyl silanetriol, APST) and phosphonate-based (trihydroxy-silyl-propyl-methyl-phosphonate, THSPMP) silane molecules able to provide a pseudo-zwitterionic nature under physiological pH conditions. Results confirmed that both mixed-charge pseudo-zwitterionic MSNs (ZMSN) and PEG-MSN display a significant reduction of serum protein adhesion and macrophages uptake with respect to pristine MSNs. In the case of ZMSNs, this reduction is up to a 70-90% for protein adsorption and c.a. 60% for cellular uptake. This pseudo-zwitterionic modification has been focused on the aim of local treatment of bacterial infections through the synergistic effect between the inherent antimicrobial effect of mixed-charge system and the levofloxacin antibiotic release profile. These findings open promising future expectations for the effective treatment of bacterial infections through the use of mixed-charge pseudo-zwitterionic MSNs furtive to macrophages and with antimicrobial properties. STATEMENT OF SIGNIFICANCE: Herein a novel antimicrobial mixed-charge pseudo-zwitterionic MSNs based system with low-fouling and reduced cell uptake behavior has been developed. This chemical modification has been performed by the simultaneous grafting of short chain organosilanes, containing amino and phosphonate groups, respectively. This nanocarrier has been tested for local infection treatment through the synergy between the antimicrobial effect of mixed-charge brushes and the levofloxacin antibiotic release profile.

Nanoengineered Peptide-Grafted Hyperbranched Polymers for Killing of Bacteria Monitored in Real Time via Intrinsic Aggregation-Induced Emission

Facing the global health crisis caused by drug-resistant bacteria, antimicrobial peptides and their analogues offer exciting solutions to this widespread problem. Without additionally introducing a fluorescent probe, novel nanoengineered peptide-grafted hyperbranched polymers (NPGHPs) are constructed for their combined outstanding antimicrobial activity and sensitive bacterial detection in real time. Hyperbranched polyamide amine (H-PAMAM) that exhibits aggregation-induced emission (AIE) effects is synthesized. Then, NPGHPs are prepared by ring-opening polymerization of α-amino acid N-carboxyanhydrides on the periphery of the H-PAMAM. The NPGHPs exhibit high-efficiency antibacterial properties against a wide spectrum of bacteria, especially against Gram-negative bacteria. On the basis of the AIE effect of NPGHPs, the interaction between NPGHPs and Escherichia coli is explored and the fluorescence intensity of NPGHPs is dependent on the number of E. coli present. Thus, a method for monitoring E. coli concentration is developed, and the detection limit is 1 × 10⁴ CFU mL^-1. Furthermore, NPGHPs are used as fluorescent probes to visualize antibacterial process via lighting-up bacteria. NPGHPs can penetrate the membrane of bacteria and cause cell rupture and apoptosis. In addition, the excellent selectivity of NPGHPs toward bacteria over mammalian cells makes them bright prospects for clinical applications.

Drug Delivery and Bone Infection

Bone infection represents greatest challenge in public health care with serious social and economic implications. The efforts of the scientific community are focused in the development of innovative and advanced biomaterials with anti-infective properties related to their non-fouling, bactericidal and/or antibiofilm capabilities. This chapter aims at thoroughly surveying the different approaches based on silica mesoporous materials (SMMs) for bone infection management. Bacteria repelling surfaces by zwitterionization process, bactericidal effect by implantable devices with antimicrobial local delivery agents and antibiofilm effect by more sophisticated systems based on targeted nanocarriers will be considered.

Mesoporous silica nanoparticles decorated with polycationic dendrimers for infection treatment

This work aims to provide an effective and novel solution for the treatment of infection by using nanovehicles loaded with antibiotics capable of penetrating the bacterial wall, thus increasing the antimicrobial effectiveness. These nanosystems, named "nanoantibiotics", are composed of mesoporous silica nanoparticles (MSNs), which act as nanocarriers of an antimicrobial agent (levofloxacin, LEVO) localized inside the mesopores. To provide the nanosystem of bacterial membrane interaction capability, a polycationic dendrimer, concretely the poly(propyleneimine) dendrimer of third generation (G3), was covalently grafted to the external surface of the LEVO-loaded MSNs. After physicochemical characterization of this nanoantibiotic, the release kinetics of LEVO and the antimicrobial efficacy of each released dosage were evaluated. Besides, internalization studies of the MSNs functionalized with the G3 dendrimer were carried out, showing a high penetrability throughout Gram-negative bacterial membranes. This work evidences that the synergistic combination of polycationic dendrimers as bacterial membrane permeabilization agents with LEVO-loaded MSNs triggers an efficient antimicrobial effect on Gram-negative bacterial biofilm. These positive results open up very promising expectations for their potential application in new infection therapies.

STATEMENT OF SIGNIFICANCE

Seeking new alternatives to current available treatments of bacterial infections represents a great challenge in nanomedicine. This work reports the design and optimization of a new class of antimicrobial agent, named "nanoantibiotic", based on mesoporous silica nanoparticles (MSNs) decorated with polypropyleneimine dendrimers of third generation (G3) and loaded with levofloxacin (LEVO) antibiotic. The covalently grafting of these G3 dendrimers to MSNs allows an effective internalization in Gram-negative bacteria. Furthermore, the LEVO loaded into the mesoporous cavities is released in a sustained manner at effective antimicrobial dosages. The novelty and originality of this manuscript relies on proving that the synergistic combination of bacteria-targeting and antimicrobial agents into a unique nanosystem provokes a remarkable antimicrobial effect against bacterial biofilm.

Combating multidrug-resistant Gram-negative bacteria with structurally nanoengineered antimicrobial peptide polymers

With the recent emergence of reports on resistant Gram-negative 'superbugs', infections caused by multidrug-resistant (MDR) Gram-negative bacteria have been named as one of the most urgent global health threats due to the lack of effective and biocompatible drugs. Here, we show that a class of antimicrobial agents, termed 'structurally nanoengineered antimicrobial peptide polymers' (SNAPPs) exhibit sub-μM activity against all Gram-negative bacteria tested, including ESKAPE and colistin-resistant and MDR (CMDR) pathogens, while demonstrating low toxicity. SNAPPs are highly effective in combating CMDR Acinetobacter baumannii infections in vivo, the first example of a synthetic antimicrobial polymer with CMDR Gram-negative pathogen efficacy. Furthermore, we did not observe any resistance acquisition by A. baumannii (including the CMDR strain) to SNAPPs. Comprehensive analyses using a range of microscopy and (bio)assay techniques revealed that the antimicrobial activity of SNAPPs proceeds via a multimodal mechanism of bacterial cell death by outer membrane destabilization, unregulated ion movement across the cytoplasmic membrane and induction of the apoptotic-like death pathway, possibly accounting for why we did not observe resistance to SNAPPs in CMDR bacteria. Overall, SNAPPs show great promise as low-cost and effective antimicrobial agents and may represent a weapon in combating the growing threat of MDR Gram-negative bacteria.

Polydopamine Hollow Nanoparticle Functionalized with N-diazeniumdiolates as a Nitric Oxide Delivery Carrier for Antibacterial Therapy

A biocompatible nitric oxide (NO) delivery nanoplatform, whose structure is a hollow nanoparticle composed of polydopamine backbone and diazeniumdiolates functional groups, is developed for antibacterial therapy. This platform liberates high NO quantitis and exerts the antibacterial activity with excellent biocompatibility thus being promising for treating bacterial infections.

Global Dissemination of Carbapenemase-Producing Klebsiella pneumoniae: Epidemiology, Genetic Context, Treatment Options, and Detection Methods

The emergence of carbapenem-resistant Gram-negative pathogens poses a serious threat to public health worldwide. In particular, the increasing prevalence of carbapenem-resistant Klebsiella pneumoniae is a major source of concern. K. pneumoniae carbapenemases (KPCs) and carbapenemases of the oxacillinase-48 (OXA-48) type have been reported worldwide. New Delhi metallo-β-lactamase (NDM) carbapenemases were originally identified in Sweden in 2008 and have spread worldwide rapidly. In this review, we summarize the epidemiology of K. pneumoniae producing three carbapenemases (KPCs, NDMs, and OXA-48-like). Although the prevalence of each resistant strain varies geographically, K. pneumoniae producing KPCs, NDMs, and OXA-48-like carbapenemases have become rapidly disseminated. In addition, we used recently published molecular and genetic studies to analyze the mechanisms by which these three carbapenemases, and major K. pneumoniae clones, such as ST258 and ST11, have become globally prevalent. Because carbapenemase-producing K. pneumoniae are often resistant to most β-lactam antibiotics and many other non-β-lactam molecules, the therapeutic options available to treat infection with these strains are limited to colistin, polymyxin B, fosfomycin, tigecycline, and selected aminoglycosides. Although, combination therapy has been recommended for the treatment of severe carbapenemase-producing K. pneumoniae infections, the clinical evidence for this strategy is currently limited, and more accurate randomized controlled trials will be required to establish the most effective treatment regimen. Moreover, because rapid and accurate identification of the carbapenemase type found in K. pneumoniae may be difficult to achieve through phenotypic antibiotic susceptibility tests, novel molecular detection techniques are currently being developed.

The bacterial type III secretion system as a target for developing new antibiotics

Antibiotic resistance in pathogens requires new targets for developing novel antibacterials. The bacterial type III secretion system (T3SS) is an attractive target for developing antibacterials as it is essential in the pathogenesis of many Gram-negative bacteria. The T3SS consists of structural proteins, effectors, and chaperones. Over 20 different structural proteins assemble into a complex nanoinjector that punctures a hole on the eukaryotic cell membrane to allow the delivery of effectors directly into the host cell cytoplasm. Defects in the assembly and function of the T3SS render bacteria non-infective. Two major classes of small molecules, salicylidene acylhydrazides and thiazolidinones, have been shown to inhibit multiple genera of bacteria through the T3SS. Many additional chemically and structurally diverse classes of small molecule inhibitors of the T3SS have been identified as well. While specific targets within the T3SS of a few inhibitors have been suggested, the vast majority of specific protein targets within the T3SS remain to be identified or characterized. Other T3SS inhibitors include polymers, proteins, and polypeptides mimics. In addition, T3SS activity is regulated by its interaction with biologically relevant molecules, such as bile salts and sterols, which could serve as scaffolds for drug design.

Fast and Accurate Large-Scale Detection of β-Lactamase Genes Conferring Antibiotic Resistance

Fast detection of β-lactamase (bla) genes allows improved surveillance studies and infection control measures, which can minimize the spread of antibiotic resistance. Although several molecular diagnostic methods have been developed to detect limited bla gene types, these methods have significant limitations, such as their failure to detect almost all clinically available bla genes. We developed a fast and accurate molecular method to overcome these limitations using 62 primer pairs, which were designed through elaborate optimization processes. To verify the ability of this large-scale bla detection method (large-scaleblaFinder), assays were performed on previously reported bacterial control isolates/strains. To confirm the applicability of the large-scaleblaFinder, the assays were performed on unreported clinical isolates. With perfect specificity and sensitivity in 189 control isolates/strains and 403 clinical isolates, the large-scaleblaFinder detected almost all clinically available bla genes. Notably, the large-scaleblaFinder detected 24 additional unreported bla genes in the isolates/strains that were previously studied, suggesting that previous methods detecting only limited types of bla genes can miss unexpected bla genes existing in pathogenic bacteria, and our method has the ability to detect almost all bla genes existing in a clinical isolate. The ability of large-scaleblaFinder to detect bla genes on a large scale enables prompt application to the detection of almost all bla genes present in bacterial pathogens. The widespread use of the large-scaleblaFinder in the future will provide an important aid for monitoring the emergence and dissemination of bla genes and minimizing the spread of resistant bacteria.

Educational effectiveness, target, and content for prudent antibiotic use

Widespread antimicrobial use and concomitant resistance have led to a significant threat to public health. Because inappropriate use and overuse of antibiotics based on insufficient knowledge are one of the major drivers of antibiotic resistance, education about prudent antibiotic use aimed at both the prescribers and the public is important. This review investigates recent studies on the effect of interventions for promoting prudent antibiotics prescribing. Up to now, most educational efforts have been targeted to medical professionals, and many studies showed that these educational efforts are significantly effective in reducing antibiotic prescribing. Recently, the development of educational programs to reduce antibiotic use is expanding into other groups, such as the adult public and children. The investigation of the contents of educational programs for prescribers and the public demonstrates that it is important to develop effective educational programs suitable for each group. In particular, it seems now to be crucial to develop appropriate curricula for teaching medical and nonmedical (pharmacy, dentistry, nursing, veterinary medicine, and midwifery) undergraduate students about general medicine, microbial virulence, mechanism of antibiotic resistance, and judicious antibiotic prescribing.