Bacteria-Targeting Conjugates Based on Antimicrobial Peptide for Bacteria Diagnosis and Therapy

Dual Antibiotic Approach: Synthesis and Antibacterial Activity of Antibiotic-Antimicrobial Peptide Conjugates

In recent years, bacterial resistance to conventional antibiotics has become a major concern in the medical field. The global misuse of antibiotics in clinics, personal use, and agriculture has accelerated this resistance, making infections increasingly difficult to treat and rendering new antibiotics ineffective more quickly. Finding new antibiotics is challenging due to the complexity of bacterial mechanisms, high costs and low financial incentives for the development of new molecular scaffolds, and stringent regulatory requirements. Additionally, innovation has slowed, with many new antibiotics being modifications of existing drugs rather than entirely new classes. Antimicrobial peptides (AMPs) are a valid alternative to small-molecule antibiotics offering several advantages, including broad-spectrum activity and a lower likelihood of inducing resistance due to their multifaceted mechanisms of action. However, AMPs face challenges such as stability issues in physiological conditions, potential toxicity to human cells, high production costs, and difficulties in large-scale manufacturing. A reliable strategy to overcome the drawbacks associated with the use of small-molecule antibiotics and AMPs is combination therapy, namely the simultaneous co-administration of two or more antibiotics or the synthesis of covalently linked conjugates. This review aims to provide a comprehensive overview of the literature on the development of antibiotic-AMP conjugates, with a particular emphasis on critically analyzing the design and synthetic strategies employed in their creation. In addition to the synthesis, the review will also explore the reported antibacterial activity of these conjugates and, where available, examine any data concerning their cytotoxicity.

Progress and challenges in bacterial infection theranostics based on functional metal nanoparticles

The rapid proliferation and infection of bacteria, especially multidrug-resistant bacteria, have become a great threat to global public health. Focusing on the emergence of "super drug-resistant bacteria" caused by the abuse of antibiotics and the insufficient and delayed early diagnosis of bacterial diseases, it is of great research significance to develop new technologies and methods for early targeted detection and treatment of bacterial infection. The exceptional effects of metal nanoparticles based on their unique physical and chemical properties make such systems ideal for the detection and treatment of bacterial infection both in vitro and in vivo. Metal nanoparticles also have admirable clinical application prospects due to their broad antibacterial spectrum, various antibacterial mechanisms and excellent biocompatibility. Herein, we summarized the research progress concerning the mechanism of metal nanoparticles in terms of antibacterial activity together with the detection of bacterial. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. Based on these observations, we also give a brief discussion on the current problems and perspective outlook of metal nanoparticles in the diagnosis and treatment of bacterial infection.

Evaluation of bacteriophage ϕ11 host recognition protein and its host-binding peptides for diagnosing/targeting Staphylococcus aureus infections

BACKGROUND

Evaluating the potential of using both synthetic and biological products as targeting agents for the diagnosis, imaging, and treatment of infections due to particularly antibiotic-resistant pathogens is important for controlling infections. This study examined the interaction between Gp45, a receptor-binding protein of the ϕ11 lysogenic phage, and its host Staphylococcus aureus (S. aureus), a common cause of nosocomial infections.

METHODS

Using molecular dynamics and docking simulations, this study identified the peptides that bind to S. aureus wall teichoic acids via Gp45. It compared the binding affinity of Gp45 and the two highest-scoring peptide sequences (P1 and P3) and their scrambled forms using microscopy, spectroscopy, and ELISA.

RESULTS

It was found that rGp45 (recombinant Gp45) and chemically synthesised P1 had a higher binding affinity for S. aureus compared with all other peptides, except for Escherichia coli. Furthermore, rGp45 had a capture efficiency of > 86%; P1 had a capture efficiency of > 64%.

CONCLUSION

These findings suggest that receptor-binding proteins such as rGp45, which provide a critical initiation of the phage life cycle for host adsorption, might play an important role in the diagnosis, imaging, and targeting of bacterial infections. Studying such proteins could accordingly enable the development of effective strategies for controlling infections.

Advances in the targeted theragnostics of osteomyelitis caused by Staphylococcus aureus

Bone infections caused by Staphylococcus aureus may lead to an inflammatory condition called osteomyelitis, which results in progressive bone loss. Biofilm formation, intracellular survival, and the ability of S. aureus to evade the immune response result in recurrent and persistent infections that present significant challenges in treating osteomyelitis. Moreover, people with diabetes are prone to osteomyelitis due to their compromised immune system, and in life-threatening cases, this may lead to amputation of the affected limbs. In most cases, bone infections are localized; thus, early detection and targeted therapy may prove fruitful in treating S. aureus-related bone infections and preventing the spread of the infection. Specific S. aureus components or overexpressed tissue biomarkers in bone infections could be targeted to deliver active therapeutics, thereby reducing drug dosage and systemic toxicity. Compounds like peptides and antibodies can specifically bind to S. aureus or overexpressed disease markers and combining these with therapeutics or imaging agents can facilitate targeted delivery to the site of infection. The effectiveness of photodynamic therapy and hyperthermia therapy can be increased by the addition of targeting molecules to these therapies enabling site-specific therapy delivery. Strategies like host-directed therapy focus on modulating the host immune mechanisms or signaling pathways utilized by S. aureus for therapeutic efficacy. Targeted therapeutic strategies in conjunction with standard surgical care could be potential treatment strategies for S. aureus-associated osteomyelitis to overcome antibiotic resistance and disease recurrence. This review paper presents information about the targeting strategies and agents for the therapy and diagnostic imaging of S. aureus bone infections.

Oligonucleotide probes for imaging and diagnosis of bacterial infections

The rise of infectious diseases as a public health concern has necessitated the development of rapid and precise diagnostic methods. Imaging techniques like nuclear and optical imaging provide the ability to diagnose infectious diseases within the body, eliminating delays caused by sampling and pre-enrichments of clinical samples and offering spatial information that can aid in a more informed diagnosis. Traditional molecular probes are typically created to image infected tissue without accurately identifying the pathogen. In contrast, oligonucleotides can be tailored to target specific RNA sequences, allowing for the identification of pathogens, and even generating antibiotic susceptibility profiles by focusing on drug resistance genes. Despite the benefits that nucleic acid mimics (NAMs) have provided in terms of stabilizing oligonucleotides, the inadequate delivery of these relatively large molecules into the cytoplasm of bacteria remains a challenge for widespread use of this technology. This review summarizes the key advancements in the field of oligonucleotide probes for in vivo imaging, highlighting the most promising delivery systems described in the literature for developing optical imaging through in vivo hybridization.

Expert opinion on antimicrobial therapies: is there enough scientific evidence to state that targeted therapies outperform non-targeted ones?

INTRODUCTION

Different active and passive strategies have been developed to fight against pathogenic bacteria. Those actions are undertaken to reduce the bacterial burden while minimizing the possibilities to develop not only antimicrobial resistance but also antimicrobial side-effects such as allergic or hypersensitivity reactions.

AREAS COVERED

We have reviewed preclinical results that evidence that targeted antimicrobial therapies outperform non-targeted ones. Active selective targeting against pathogenic bacteria has been achieved through the functionalization of antimicrobials, either alone or encapsulated within micro- or nanocarriers, with various recognition moieties. These moieties include peptides, aptamers, antibodies, carbohydrates, extracellular vesicles, cell membranes, infective agents, and other affinity ligands with specific bacterial tropism. Those selective ligands increase retention and enhance effectiveness reducing the side-effects and the required dose to exert the antimicrobial action at the site of infection.

EXPERT OPINION

When using targeted antimicrobial therapies not only reduced side-effects are observed, but also, compared to the administration of equivalent doses of the non-targeted drugs, a superior efficacy has been demonstrated against planktonic, sessile, and intracellular pathogenic bacterial persisters. The translation of those targeted therapies to subsequent phases of clinical development still requires the demonstration of a reduction in the probabilities for the pathogen to develop resistance when using targeted approaches.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Peptide-Drug Conjugates: An Emerging Direction for the Next Generation of Peptide Therapeutics

Building on recent advances in peptide science, medicinal chemists have developed a hybrid class of bioconjugates, called peptide-drug conjugates, that demonstrate improved efficacy compared to peptides and small molecules independently. In this Perspective, we discuss how the conjugation of synergistic peptides and small molecules can be used to overcome complex disease states and resistance mechanisms that have eluded contemporary therapies because of their multi-component activity. We highlight how peptide-drug conjugates display a multi-factor therapeutic mechanism similar to that of antibody-drug conjugates but also demonstrate improved therapeutic properties such as less-severe off-target effects and conjugation strategies with greater site-specificity. The many considerations that go into peptide-drug conjugate design and optimization, such as peptide/small-molecule pairing and chemo-selective chemistries, are discussed. We also examine several peptide-drug conjugate series that demonstrate notable activity toward complex disease states such as neurodegenerative disorders and inflammation, as well as viral and bacterial targets with established resistance mechanisms.

Antimicrobial peptides: An alternative to traditional antibiotics

As antibiotic-resistant bacteria and genes continue to emerge, the identification of effective alternatives to traditional antibiotics has become a pressing issue. Antimicrobial peptides are favored for their safety, low residue, and low resistance properties, and their unique antimicrobial mechanisms show significant potential in combating antibiotic resistance. However, the high production cost and weak activity of antimicrobial peptides limit their application. Moreover, traditional laboratory methods for identifying and designing new antimicrobial peptides are time-consuming and labor-intensive, hindering their development. Currently, novel technologies, such as artificial intelligence (AI) are being employed to develop and design new antimicrobial peptide resources, offering new opportunities for the advancement of antimicrobial peptides. This article summarizes the basic characteristics and antimicrobial mechanisms of antimicrobial peptides, as well as their advantages and limitations, and explores the application of AI in antimicrobial peptides prediction amd design. This highlights the crucial role of AI in enhancing the efficiency of antimicrobial peptide research and provides a reference for antimicrobial drug development.

Radiosynthesis and Bioevaluation of 99mTc-Labeled Isocyanide Ubiquicidin 29-41 Derivatives as Potential Agents for Bacterial Infection Imaging

To develop a novel 99mTc-labeled ubiquicidin 29-41 derivative for bacterial infection single-photon emission computed tomography (SPECT) imaging with improved target-to-nontarget ratio and lower nontarget organ uptake, a series of isocyanide ubiquicidin 29-41 derivatives (CNnUBI 29-41, n = 5-9) with different carbon linkers were designed, synthesized and radiolabeled with the [99mTc]Tc(I)+ core, [99mTc][Tc(I)(CO)3(H2O)3]+ core and [99mTc][Tc(V)N]2+ core. All the complexes are hydrophilic, maintain good stability and specifically bind Staphylococcus aureus in vitro. The biodistribution in mice with bacterial infection and sterile inflammation demonstrated that [99mTc]Tc-CN5UBI 29-41 was able to distinguish bacterial infection from sterile inflammation, which had an improved abscess uptake and a greater target-to-nontarget ratio. SPECT imaging study of [99mTc]Tc-CN5UBI 29-41 in bacterial infection mice showed that there was a clear accumulation in the infection site, suggesting that this radiotracer could be a potential radiotracer for bacterial infection imaging.

No country for old antibiotics! Antimicrobial peptides (AMPs) as next-generation treatment for skin and soft tissue infection

In recent years, the unprecedented rise of bacterial antibiotic resistance together with the lack of adequate therapies have made the treatment of skin infections and chronic wounds challenging, urging the scientific community to focus on the development of new and more efficient treatment strategies. In this context, there is a growing interest in the use of natural molecules with antimicrobial features, capable of supporting wound healing i.e., antimicrobial peptides (AMPs), for the treatment of skin and soft tissue infections. In this review, we give a short overview of the bacterial skin infections as well as some of the classic treatments used for topical application. We then summarize the AMPs classes, stressing the importance of the appropriate selection of the peptides based on their characteristics and physicochemical properties in order to maximize the antibacterial efficacy of the therapeutic systems against multi-drug resistant pathogens. Additionally, the present paper provides a comprehensive and rigorous assessment of the latest clinical trials investigating the efficacy of AMPs in the treatment of skin and soft tissue infections, highlighting the relevant outcomes. Seeking to obtain novel and improved compounds with synergistic activity, while also decreasing some of the known side effects of AMPs, we present two employed strategies using AMPs: (i) AMPs-conjugated nanosystems for systemic and topical drug delivery systems and (ii) antibiotics-peptide conjugates as a strategy to overcome antibiotics resistance. Finally, an important property of some of the AMPs used in wound treatment is highlighted: their ability to help in wound healing by generally promoting cell proliferation and migration, and in some cases re-epithelialization and angiogenesis among others. Thus, as the pursuit of improvement is an ongoing effort, this work presents the advances made in the treatment of skin and soft tissue infections along with their advantages and limitations, while the still remaining challenges are addressed by providing future prospects and strategies to overcome them.

Chloramphenicol Derivatization in Its Primary Hydroxyl Group with Basic Amino Acids Leads to New Pharmacophores with High Antimicrobial Activity

In a previous study published by our group, successful modification of the antibiotic chloramphenicol (CHL) was reported, which was achieved by replacing the dichloroacetyl tail with alpha and beta amino acids, resulting in promising new antibacterial pharmacophores. In this study, CHL was further modified by linking the basic amino acids lysine, ornithine, and histidine to the primary hydroxyl group of CHL via triazole, carbamate, or amide bonding. Our results showed that while linking the basic amino acids retained antibacterial activity, it was somewhat reduced compared to CHL. However, in vitro testing demonstrated that all derivatives were comparable in activity to CHL and competed for the same ribosomal binding site with radioactive chloramphenicol. The amino acid-CHL tethering modes were evaluated either with carbamate (7, 8) derivatives, which exhibited higher activity, or with amide- (4-6) or triazole-bridged compounds (1-3), which were equally potent. Our findings suggest that these new pharmacophores have potential as antimicrobial agents, though further optimization is needed.

Release of immunomodulatory peptides at bacterial membrane interfaces as a novel strategy to fight microorganisms

Cationic and amphiphilic peptides can be used as homing devices to accumulate conjugated antibiotics to bacteria-enriched sites and promote efficient microbial killing. However, just as important as tackling bacterial infections, is the modulation of the immune response in this complex microenvironment. In the present report, we designed a peptide chimaera called Chim2, formed by a membrane-active module, an enzyme hydrolysis site, and a formyl peptide receptor 2 (FPR2) agonist. This molecule was designed to adsorb onto bacterial membranes, promote their lysis, and upon hydrolysis by local enzymes, release the FPR2 agonist sequence for activation and recruitment of immune cells. We synthesized the isolated peptide modules of Chim2 and characterized their biological activities independently and as a single polypeptide chain. We conducted antimicrobial assays, along with other tests aiming at the analyses of the cellular and immunological responses. In addition, assays using vesicles as models of eukaryotic and prokaryotic membranes were conducted, and solution structures of Chim2 were generated by ¹H NMR. Chim2 is antimicrobial, adsorbs preferentially to negatively charged vesicles while adopting an α-helix structure, and exposes its disorganized tail to the solvent, which facilitates hydrolysis by tryptase-like enzymes, allowing the release of the FPR2 agonist fragment. This fragment was shown to induce accumulation of the cellular activation marker, lipid bodies, in mouse macrophages and the release of immunomodulatory interleukins. In conclusion, these data demonstrate that peptides with antimicrobial and immunomodulatory activities can be considered for further development as drugs.

Nanocarriers for the delivery of antibiotics into cells against intracellular bacterial infection

The barrier function of host cells enables intracellular bacteria to evade the lethality of the host immune system and antibiotics, thereby causing chronic and recurrent infections that seriously threaten human health. Currently, the main clinical strategy for the treatment of intracellular bacterial infections involves the use of long-term and high-dose antibiotics. However, insufficient intracellular delivery of antibiotics along with various resistance mechanisms not only weakens the efficacy of current therapies but also causes serious adverse drug reactions, further increasing the disease and economic burden. Improving the delivery efficiency, intracellular accumulation, and action time of antibiotics remains the most economical and effective way to treat intracellular bacterial infections. The rapid development of nanotechnology provides a strategy to efficiently deliver antibiotics against intracellular bacterial infections into cells. In this review, we summarize the types of common intracellular pathogens, the difficulties faced by antibiotics in the treatment of intracellular bacterial infections, and the research progress of several types of representative nanocarriers for the delivery of antibiotics against intracellular bacterial infections that have emerged in recent years. This review is expected to provide a reference for further elucidating the intracellular transport mechanism of nanocarrier-drug complexes, designing safer and more effective nanocarriers and establishing new strategies against intracellular bacterial infection.

A radio- and fluorescently labelled tracer for imaging and quantification of bacterial infection on orthopaedic prostheses : a proof of principle study

AIMS

Arthroplasty surgery of the knee and hip is performed in two to three million patients annually. Periprosthetic joint infections occur in 4% of these patients. Debridement, antibiotics, and implant retention (DAIR) surgery aimed at cleaning the infected prosthesis often fails, subsequently requiring invasive revision of the complete prosthetic reconstruction. Infection-specific imaging may help to guide DAIR. In this study, we evaluated a bacteria-specific hybrid tracer (^99mTc-UBI_29-41-Cy5) and its ability to visualize the bacterial load on femoral implants using clinical-grade image guidance methods.

METHODS

^99mTc-UBI_29-41-Cy5 specificity for Stapylococcus aureus was assessed in vitro using fluorescence confocal imaging. Topical administration was used to highlight the location of S. aureus cultured on femoral prostheses using fluorescence imaging and freehand single photon emission CT (fhSPECT) scans. Gamma counting and fhSPECT were used to quantify the bacterial load and monitor cleaning with chlorhexidine. Microbiological culturing helped to relate the imaging findings with the number of (remaining) bacteria.

RESULTS

Bacteria could be effectively stained in vitro and on prostheses, irrespective of the presence of biofilm. Infected prostheses revealed bacterial presence on the transition zone between the head and neck, and in the screw hole. Qualitative 2D fluorescence images could be complemented with quantitative 3D fhSPECT scans. Despite thorough chlorhexidine treatments, 28% to 44% of the signal remained present in the locations of the infection that were identified using imaging, which included 500 to 2,000 viable bacteria.

CONCLUSION

The hybrid tracer ^99mTc-UBI_29-41-Cy5 allowed effective bacterial staining. Qualitative real-time fluorescence guidance could be effectively combined with nuclear imaging that enables quantitative monitoring of the effectiveness of cleaning strategies.Cite this article: Bone Joint Res 2023;12(1):72-79.

Chemically Enhanced Immunogenicity of Bacteria by Supramolecular Functionalization with an Adjuvant

Many pathogens blunt immune responses because they lack immunogenic structural features, which typically results in disease. Here, we show evidence suggesting that pathogen immunogenicity can be chemically enhanced. Using supramolecular host-guest chemistry, we complexed onto the surface of a poorly immunogenic bacterium (Staphylococcus aureus) a TLR7 agonist-based adjuvant. "Adjuvanted" bacteria were readily recognized by macrophages and induced a more pro-inflammatory immunophenotype. Future applications of this concept could yield treatment modalities that bolster the immune system's response to pathogenic microbes.

Development of Antimicrobial Peptide-Antibiotic Conjugates to Improve the Outer Membrane Permeability of Antibiotics Against Gram-Negative Bacteria

Antibiotics have been widely used in the medical field as a treatment for infectious diseases, but they are not effective against all Gram-negative bacteria because of their low permeability to the outer membrane. One of the strategies to improve the antibacterial activity of antibiotics is the coadministration of antibiotics and membrane-perturbing antimicrobial peptides for their synergistic effects. However, because of their different pharmacokinetics, their coadministration may not exert expected effects in the clinical stage. Here, we designed various antimicrobial peptide-antibiotic conjugates as a novel approach to improve the antimicrobial activity of antibiotics. Ampicillin was chosen as a model antibiotic with poor outer membrane permeability, and the effects of the chemistry and position of conjugation and the choice of antimicrobial peptides were examined. One of the ampicillin conjugates exhibited significantly improved antimicrobial activity against ampicillin-resistant Gram-negative bacteria without exerting cytotoxicity against human cultured cells, demonstrating that our novel approach is an effective strategy to improve the antimicrobial activity of antibiotics with low outer membrane permeability.

Recent advances in prevention, detection and treatment in prosthetic joint infections of bioactive materials

Prosthetic joint infection (PJI) is often considered as one of the most common but catastrophic complications after artificial joint replacement, which can lead to surgical failure, revision, amputation and even death. It has become a worldwide problem and brings great challenges to public health systems. A small amount of microbe attaches to the graft and forms a biofilm on its surface, which lead to the PJI. The current standard methods of treating PJI have limitations, but according to recent reports, bioactive materials have potential research value as a bioactive substance that can have a wide range of applications in the field of PJI. These include the addition of bioactive materials to bone cement, the use of antibacterial and anti-fouling materials for prosthetic coatings, the use of active materials such as bioactive glasses, protamine, hydrogels for prophylaxis and detection with PH sensors and fluorescent-labelled nanoparticles, and the use of antibiotic hydrogels and targeting delivery vehicles for therapeutic purposes. This review focus on prevention, detection and treatment in joint infections with bioactive materials and provide thoughts and ideas for their future applications.

Engineering Approaches for the Development of Antimicrobial Peptide-Based Antibiotics

Antimicrobial peptides (AMPs) have received increasing attention as potential alternatives for future antibiotics because of the rise of multidrug-resistant (MDR) bacteria. AMPs are small cationic peptides with broad-spectrum antibiotic activities and different action mechanisms to those of traditional antibiotics. Despite the desirable advantages of developing peptide-based antimicrobial agents, the clinical applications of AMPs are still limited because of their enzymatic degradation, toxicity, and selectivity. In this review, structural modifications, such as amino acid substitution, stapling, cyclization of peptides, and hybrid AMPs with conventional antibiotics or other peptides, will be presented. Additionally, nanodelivery systems using metals or lipids to deliver AMPs will be discussed based on the structural properties and action mechanisms of AMPs.

Medicinal Chemistry of Inhibitors Targeting Resistant Bacteria

The discovery of antibiotics was a revolutionary feat that provided countless health benefits. The identification of penicillin by Alexander Fleming initiated the era of antibiotics, represented by constant discoveries that enabled effective treatments for the different classes of diseases caused by bacteria. However, the indiscriminate use of these drugs allowed the emergence of resistance mechanisms of these microorganisms against the available drugs. In addition, the constant discoveries in the 20th century generated a shortage of new molecules, worrying health agencies and professionals about the appearance of multidrug-resistant strains against available drugs. In this context, the advances of recent years in molecular biology and microbiology have allowed new perspectives in drug design and development, using the findings related to the mechanisms of bacterial resistance to generate new drugs that are not affected by such mechanisms and supply new molecules to be used to treat resistant bacterial infections. Besides, a promising strategy against bacterial resistance is the combination of drugs through adjuvants, providing new expectations in designing new antibiotics and new antimicrobial therapies. Thus, this manuscript will address the main mechanisms of bacterial resistance under the understanding of medicinal chemistry, showing the main active compounds against efflux mechanisms, and also the application of the use of drug delivery systems, and finally, the main potential natural products as adjuvants or with promising activity against resistant strains.

Liposome Delivery of Nucleic Acids in Bacteria: Toward In Vivo Labeling of Human Microbiota

Development of specific probes to study the in vivo spatial distribution of microorganisms is essential to understand the ecology of human microbiota. Herein, we assess the possibility of using liposomes loaded with fluorescently labeled nucleic acid mimics (LipoNAMs) to image Gram-negative and Gram-positive bacteria. We proved that liposome fusion efficiencies were similar in both Gram-negative and Gram-positive bacteria but that the efficiency was highly dependent on the lipid concentration. Notably, LipoNAMs were significantly more effective for the internalization of oligonucleotides in bacteria than the fixation/permeabilization methods commonly used in vitro. Furthermore, a structural and morphological assessment of the changes on bacteria allowed us to observe that liposomes increased the permeability of the cell envelope especially in Gram-negative bacteria. Considering the delivery efficiency and permeabilization effect, lipid concentrations of approximately 5 mM should be selected to maximize the detection of bacteria without compromising the bacterial cellular structure.

Florfenicol-Polyarginine Conjugates Exhibit Promising Antibacterial Activity Against Resistant Strains

Florfenicol was widely used as antibiotic in the livestock and poultry breeding industry, resulting in a serious problem of drug resistance. In order to solve the resistance of florfenicol, this study designed and synthesized a new series of florfenicol-polyarginine conjugates and tested for antimicrobial activities. Drug-sensitive bacteria, gram-negative bacteria Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus), were sensitive to several of the compounds tested. These conjugates also showed excellent activity against drug-resistant strains such as methicillin-resistant S. aureus (MRSA) and florfenicol resistant Escherichia coli strains (2017XJ30, 2019XJ20), one of which as E6 had a minimum inhibitory concentration of 12.5 μmol/L. These conjugates did not allow bacteria to develop resistance and also decreased bacterial growth by membrane depolarization and disruption. Additionally, florfenicol succinate (C1) showed certain activity after coupling with arginine. This suggested that conjugating arginine to florfenicol succinate effectively modulated the properties of prodrugs. These new conjugates may provide useful insights for expanding the pool of antibiotics.

Strategies to Improve the Activity and Biocompatibility: Modification of Peptide Antibiotics

As host defense peptides, peptide antibiotics exist in almost all organisms. Many of their activities come from their inactivation of bacteria, yeast, fungi, and even cancer cells. However, natural peptide antibiotics are relatively poor in stability and penetration, and have high hemolytic properties, which makes them difficult to directly apply. Therefore, natural peptide antibiotics can be modified to enhance their activity and biocompatibility. Based on the characteristics of amino acids, amino acid substitutions can be performed to study the effect of amino acid types on the activity of peptide antibiotics. The design of ultrashort peptides, cyclic peptides, and self-assembling peptides is also a way to improve the activity of peptide antibiotics. In addition, antibacterial peptides can also be conjugated with antibiotics, lipids, or metal ions to prepare antibacterial peptides with special activities. This review introduces several methods for modifying peptide antibiotics and their specific applications, providing a theoretical basis for the further application of peptide antibiotics.

Molecular imaging approaches to facilitate bacteria-mediated cancer therapy

Bacteria-mediated cancer therapy is a potential therapeutic strategy for cancer that has unique properties, including broad tumor-targeting ability, various administration routes, the flexibility of delivery, and facilitating the host's immune responses. The molecular imaging of bacteria-mediated cancer therapy allows the therapeutically injected bacteria to be visualized and confirms the accurate delivery of the therapeutic bacteria to the target lesion. Several hurdles make bacteria-specific imaging challenging, including the need to discriminate therapeutic bacterial infection from inflammation or other pathologic lesions. To realize the full potential of bacteria-specific imaging, it is necessary to develop bacteria-specific targets that can be associated with an imaging assay. This review describes the current status of bacterial imaging techniques together with the advantages and disadvantages of several imaging modalities. Also, we describe potential targets for bacterial-specific imaging and related applications.

Amphiphilic cyclic peptide [W4KR5]-Antibiotics combinations as broad-spectrum antimicrobial agents

Linear and cyclic amphiphilic peptides, (W₄KR₅) and [W₄KR₅], were evaluated as antibacterial agents against Gram-positive and Gram-negative bacteria, including four multi-drug resistant strains and the corresponding four non-resistant strains. Cyclic peptide [W₄KR₅] showed higher antibacterial activity than the linear (W₄KR₅) counterpart. Cyclic [W₄KR₅] was subjected to combination (physical mixture or covalent conjugation) with meropenem as a model antibiotic to study the impact of the combination on antimicrobial activity. A physical mixture of meropenem and [W₄KR₅] showed synergistic antibacterial activity against Gram-negative P. aeruginosa (ATCC BAA-1744) and P. aeruginosa (ATCC 27883) strains. [W₄KR₅] was further subjected to extensive antibacterial studies against additional 10 bacteria strains, showing significant antibacterial efficacy against Gram-positive bacteria strains. Combinations studies of [W₄KR₅] with an additional 9 commercially available antibiotics showed significant enhancement in antibacterial activity for all tested combinations, especially with tetracycline, tobramycin, levofloxacin, clindamycin, daptomycin, polymyxin, kanamycin, and vancomycin. Time-kill kinetics assay and flow cytometry results exhibited that [W₄KR₅] had a time-dependent synergistic effect and membrane disruption property. These data indicate that [W₄KR₅] improves the antibacterial activity, presumably by facilitating the internalization of antibiotics and their interaction with the intracellular targets. This study introduces a potential strategy for treating multidrug-resistant pathogens by combining [W₄KR₅] and a variety of classical antibiotics to improve the antibacterial effectiveness.

Bone infection site targeting nanoparticle-antibiotics delivery vehicle to enhance treatment efficacy of orthopedic implant related infection

Orthopedic implants account for 99% of orthopedic surgeries, however, orthopedic implant-related infection is one of the most serious complications owing to the potential for limb-threatening sequelae and mortality. Current antibiotic treatments still lack the capacity to target bone infection sites, thereby resulting in unsatisfactory therapeutic effects. Here, the bone infection site targeting efficacy of D6 and UBI_29-41 peptides was investigated, and bone-and-bacteria dual-targeted nanoparticles (NPs) with D6 and UBI_29-41 peptides were first fabricated to target bone infection site and control the release of vancomycin in bone infection site. The results of this study demonstrated that the bone-and-bacteria dual-targeted mesoporous silica NPs exhibit excellent bone and bacteria targeting efficacy, excellent biocompatibility and effective antibacterial properties in vitro. Furthermore, in a rat model of orthopedic implant-related infection with methicillin-resistant Staphylococcus aureus, the growth of bacteria was evidently inhibited without cytotoxicity, thus realizing the early treatment of implant-related infection. Hence, the bone-and-bacteria dual-targeted molecule-modified NPs may target bacteria-infected bone sites and act as ideal candidates for the therapy of orthopedic implant-related infections.

•

A novel treatment of OII by nanoparticles targeting bone infection site was proposed.

•

Dual-targeted MSNs with D6 and UBI peptides could target the bone infection site.

•

Dual-targeted MSNs were fabricated to release vancomycin in bone infection site.

•

Dual-targeted MSNs could be used for the therapy of OII.

Antimicrobial peptides, conventional antibiotics, and their synergistic utility for the treatment of drug-resistant infections

Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), are important effector immune defense molecules in multicellular organisms. AMPs exert their antimicrobial activities through several mechanisms; thus far, induction of drug resistance through AMPs has been regarded as unlikely. Therefore, they have great potential as new generation antimicrobial agents. To date, more than 30 AMP-related drugs are in the clinical trial phase. In recent years, studies show that some AMPs and conventional antibiotics have synergistic effects. The combined use of AMPs and antibiotics can kill drug-resistant pathogens, prevent drug resistance, and significantly improve the therapeutic effects of antibiotics. In this review, we discuss the progress in synergistic studies on AMPs and conventional antibiotics. An overview of the current understanding of the functional scope of AMPs, ongoing clinical trials, and challenges in the development processes are also presented.

Peptide Multimerization as Leads for Therapeutic Development

Multimerization of peptide structures has been a logical evolution in their development as potential therapeutic molecules. The multivalent properties of these assemblies have attracted much attention from researchers in the past and the development of more complex branching dendrimeric structures, with a wide array of biocompatible building blocks is revealing previously unseen properties and activities. These branching multimer and dendrimer structures can induce greater effect on cellular targets than monomeric forms and act as potent antimicrobials, potential vaccine alternatives and promising candidates in biomedical imaging and drug delivery applications. This review aims to outline the chemical synthetic innovations for the development of these highly complex structures and highlight the extensive capabilities of these molecules to rival those of natural biomolecules.

Bacteria-Targeted MRI Probe-Based Imaging Bacterial Infection and Monitoring Antimicrobial Therapy In Vivo

Despite the significant advances of imaging techniques nowadays, accurate diagnosis of bacterial infections and real-time monitoring the efficacy of antibiotic therapy in vivo still remain huge challenges. Herein, a self-assembling peptide (FFYEGK) and vancomycin (Van) antibiotic molecule co-modified gadolinium (Gd) MRI nanoaggregate probe (GFV) for detecting Staphylococcus aureus (S. aureus) infection in vivo and monitoring the treatment of S. aureus-infected myositis by using daptomycin (Dap) antibiotic as model are designed and fabricated. The as-prepared GFV probe bears Van molecules, making itself good bacteria-specific targeting, and the peptide in the probe can enhance the longitudinal relaxivity rate (r₁ ) after self-assembly due to the π-π stacking. The study showed that, based on the GFV probe, bacterial infections and sterile inflammation can be discriminated, and as few as 10⁵ cfu S. aureus can be detected in vivo with high specificity and accurately. Moreover, the T₁ signal of GFV probe at the S. aureus-infected site in mice correlates with the increasing time of Dap treating, indicating the possibility of monitoring the efficacy of antibacterial agents for infected mice based on the as proposed GFV probe. This study shows the potential of GFV probe for diagnosis, evaluation, and prognosis of infectious diseases in clinics.

Visualizing and quantifying antimicrobial drug distribution in tissue

The biodistribution and pharmacokinetics of drugs are vital to the mechanistic understanding of their efficacy. Measuring antimicrobial drug efficacy has been challenging as plasma drug concentration is used as a surrogate for tissue drug concentration, yet typically does not reflect that at the intended site(s) of action. Utilizing an image-guided approach, it is feasible to accurately quantify the biodistribution and pharmacokinetics within the desired site(s) of action. We outline imaging modalities used in visualizing drug distribution with examples ranging from in vitro cellular drug uptake to clinical treatment of microbial infections. The imaging modalities of interest are: radio-labeling, magnetic resonance, mass spectrometry imaging, computed tomography, fluorescence, and Raman spectroscopy. We outline the progress, limitations, and future outlook for each methodology. Further advances in these optical approaches would benefit patients and researchers alike, as non-invasive imaging could yield more profound insights with a lower clinical burden than invasive measurement approaches used today.

Selective Bacterial Targeting and Infection-Triggered Release of Antibiotic Colistin Conjugates

In order to render potent, but toxic antibiotics more selective, we have explored a novel conjugation strategy that includes drug accumulation followed by infection-triggered release of the drug. Bacterial targeting was achieved using a modified fragment of the human antimicrobial peptide ubiquicidin, as demonstrated by fluorophore-tagged variants. To limit the release of the effector colistin only to infection-related situations, we introduced a linker that was cleaved by neutrophil elastase (NE), an enzyme secreted by neutrophil granulocytes at infection sites. The linker carried an optimized sequence of amino acids that was required to assure sufficient cleavage efficiency. The antibacterial activity of five regioisomeric conjugates prepared by total synthesis was masked, but was released upon exposure to recombinant NE when the linker was attached to amino acids at the 1- or the 3-position of colistin. A proof-of-concept was achieved in co-cultures of primary human neutrophils and Escherichia coli that induced the secretion of NE, the release of free colistin, and an antibacterial efficacy that was equal to that of free colistin.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Radiolabeling and evaluation of a novel [99mTcN]2+ complex with deferoxamine dithiocarbamate as a potential agent for bacterial infection imaging

In order to find a ^99mTc-labeled deferoxamine radiotracer for bacterial infection imaging, deferoxamine dithiocarbamate (DFODTC) was successfully synthesized and it was radiolabeled with [^99mTcN]²⁺ core to prepare the ^99mTcN(DFODTC)₂ complex. ^99mTcN(DFODTC)₂ was obtained with high radiochemical purity without further purification. The complex was lipophilic and exhibited good in vitro stability. According to the result of bacterial binding study, the binding of ^99mTcN(DFODTC)₂ to bacteria was specific. Biodistribution in mice study indicated that ^99mTcN(DFODTC)₂ had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses at 120 min after injection, which showed that the radiotracer could differentiate between bacterial infection and sterile inflammation. SPECT/CT images showed that there was a clear accumulation in infection sites, suggesting that ^99mTcN(DFODTC)₂ could be a potential bacterial infection imaging radiotracer.

Exploring the possible targeting strategies of liposomes against methicillin-resistant Staphylococcus aureus (MRSA)

Multi antibiotic-resistant bacterial infections are on the rise due to the overuse of antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the pathogens listed under the category of serious threats where vancomycin remains the mainstay treatment despite the availability of various antibacterial agents. Recently, decreased susceptibility to vancomycin from clinical isolates of MRSA has been reported and has drawn worldwide attention as it is often difficult to overcome and leads to increased medical costs, mortality, and longer hospital stays. Development of antibiotic delivery systems is often necessary to improve bioavailability and biodistribution, in order to reduce antibiotic resistance and increase the lifespan of antibiotics. Liposome entrapment has been used as a method to allow higher drug dosing apart from reducing toxicity associated with drugs. The surface of the liposomes can also be designed and enhanced with drug-release properties, active targeting, and stealth effects to prevent recognition by the mononuclear phagocyte system, thus enhancing its circulation time. The present review aimed to highlight the possible targeting strategies of liposomes against MRSA bacteremia systemically while investigating the magnitude of this effect on the minimum inhibitory concentration level.

New Chloramphenicol Derivatives with a Modified Dichloroacetyl Tail as Potential Antimicrobial Agents

To combat the dangerously increasing pathogenic resistance to antibiotics, we developed new pharmacophores by chemically modifying a known antibiotic, which remains to this day the most familiar and productive way for novel antibiotic development. We used as a starting material the chloramphenicol base, which is the free amine group counterpart of the known chloramphenicol molecule antibiotic upon removal of its dichloroacetyl tail. To this free amine group, we tethered alpha- and beta-amino acids, mainly glycine, lysine, histidine, ornithine and/or beta-alanine. Furthermore, we introduced additional modifications to the newly incorporated amine groups either with protecting groups triphenylmethyl- (Trt) and tert-butoxycarbonyl- (Boc) or with the dichloroacetic group found also in the chloramphenicol molecule. The antimicrobial activity of all compounds was tested both in vivo and in vitro, and according to the results, the bis-dichloroacetyl derivative of ornithine displayed the highest antimicrobial activity both in vivo and in vitro and seems to be a dynamic new pharmacophore with room for further modification and development.

Recent Progress in the Molecular Imaging of Tumor-Treating Bacteria

Bacterial cancer therapy (BCT) approaches have been extensively investigated because bacteria can show unique features of strong tropism for cancer, proliferation inside tumors, and antitumor immunity, while bacteria are also possible agents for drug delivery. Despite the rapidly increasing number of preclinical studies using BCT to overcome the limitations of conventional cancer treatments, very few BCT studies have advanced to clinical trials. In patients undergoing BCT, the precise localization and quantification of bacterial density in different body locations is important; however, most clinical trials have used subjective clinical signs and invasive sampling to confirm bacterial colonization. There is therefore a need to improve the visualization of bacterial densities using noninvasive and repetitive in vivo imaging techniques that can facilitate the clinical translation of BCT. In vivo optical imaging techniques using bioluminescence and fluorescence, which are extensively employed to image the therapeutic process of BCT in small animal research, are hard to apply to the human body because of their low penetrative power. Thus, new imaging techniques need to be developed for clinical trials. In this review, we provide an overview of the various in vivo bacteria-specific imaging techniques available for visualizing tumor-treating bacteria in BCT studies.

Comparison of two fluorescent probes in preclinical non-invasive imaging and image-guided debridement surgery of Staphylococcal biofilm implant infections

Implant-associated infections are challenging to diagnose and treat. Fluorescent probes have been heralded as a technologic advancement that can improve our ability to non-invasively identify infecting organisms, as well as guide the inexact procedure of surgical debridement. This study’s purpose was to compare two fluorescent probes for their ability to localize Staphylococcus aureus biofilm infections on spinal implants utilizing noninvasive optical imaging, then assessing the broader applicability of the more successful probe in other infection animal models. This was followed by real-time, fluorescence image-guided surgery to facilitate debridement of infected tissue. The two probe candidates, a labelled antibiotic that targets peptidoglycan (Vanco-800CW), and the other, a labelled antibody targeting the immunodominant Staphylococcal antigen A (1D9-680), were injected into mice with spine implant infections. Mice were then imaged noninvasively with near infrared fluorescent imaging at wavelengths corresponding to the two probe candidates. Both probes localized to the infection, with the 1D9-680 probe showing greater fidelity over time. The 1D9-680 probe was then tested in mouse models of shoulder implant and allograft infection, demonstrating its broader applicability. Finally, an image-guided surgery system which superimposes fluorescent signals over analog, real-time, tissue images was employed to facilitate debridement of fluorescent-labelled bacteria.

Fluorescent antibiotics for real-time tracking of pathogenic bacteria

The harm of pathogenic bacteria to humans has promoted extensive research on physiological processes of pathogens, such as the mechanism of bacterial infection, antibiotic mode of action, and bacterial antimicrobial resistance. Most of these processes can be better investigated by timely tracking of fluorophore-derived antibiotics in living cells. In this paper, we will review the recent development of fluorescent antibiotics featuring the conjugation with various fluorophores, and focus on their applications in fluorescent imaging and real-time detection for various physiological processes of bacteria in vivo.

•

Profiles of Fluorophores-derived Antibiotics in Development.

•

Discussing the influence on antibiotic activity after conjugating fluorophore.

•

Fluorescent Tracking to better understand physiological processes of Pathogenic bacteria.

•

Live-Cell imaging to investigate bacteria in their native environment.

A Fluorescent Teixobactin Analogue

This report describes the first synthesis and application of a fluorescent teixobactin analogue that exhibits antibiotic activity and binds to the cell walls of Gram-positive bacteria. The teixobactin analogue, Lys(Rhod)₉,Arg₁₀-teixobactin, has a fluorescent tag at position 9 and an arginine in place of the natural allo-enduracididine residue at position 10. The fluorescent teixobactin analogue retains partial antibiotic activity, with minimum inhibitory concentrations of 4-8 μg/mL across a panel of Gram-positive bacteria, as compared to 1-4 μg/mL for the unlabeled Arg₁₀-teixobactin analogue. Lys(Rhod)₉,Arg₁₀-teixobactin is prepared by a regioselective labeling strategy that labels Lys₉ with an amine-reactive rhodamine fluorophore during solid-phase peptide synthesis, with the resulting conjugate tolerating subsequent solid-phase peptide synthesis reactions. Treatment of Gram-positive bacteria with Lys(Rhod)₉,Arg₁₀-teixobactin results in septal and lateral staining, which is consistent with an antibiotic targeting cell wall precursors. Concurrent treatment of Lys(Rhod)₉,Arg₁₀-teixobactin and BODIPY FL vancomycin results in septal colocalization, providing further evidence that Lys(Rhod)₉,Arg₁₀-teixobactin binds to cell wall precursors. Controls with either Gram-negative bacteria, or an inactive fluorescent homologue with Gram-positive bacteria, showed little or no staining in fluorescence micrographic studies. Lys(Rhod)₉,Arg₁₀-teixobactin can thus serve as a functional probe to study Gram-positive bacteria and their interactions with teixobactin.

Imaging in Chronic Wound Diagnostics

Significance: Chronic wounds affect millions of patients worldwide, placing a huge burden on health care resources. Although significant progress has been made in the development of wound treatments, very few advances have been made in wound diagnosis. Recent Advances: Standard imaging methods like computed tomography, single-photon emission computed tomography, magnetic resonance imaging, terahertz imaging, and ultrasound imaging have been widely employed in wound diagnostics. A number of noninvasive optical imaging modalities like optical coherence tomography, near-infrared spectroscopy, laser Doppler imaging, spatial frequency domain imaging, digital camera imaging, and thermal and fluorescence imaging have emerged over the years. Critical Issues: While standard diagnostic wound imaging modalities provide valuable information, they cannot account for dynamic changes in the wound environment. In addition, they lack the capability to predict the healing outcome. Thus, there remains a pressing need for more efficient methods that can not only indicate the current state of the wound but also help determine whether the wound is on track to heal normally. Future Directions: Many imaging probes have been fabricated and shown to provide real-time assessment of tissue microenvironment and inflammatory responses in vivo. These probes have been demonstrated to noninvasively detect various changes in the wound environment, which include tissue pH, reactive oxygen species, fibrin deposition, matrix metalloproteinase production, and macrophage accumulation. This review summarizes the creation of these probes and their potential implications in wound monitoring.

Noncovalent Conjugates of Ionic Liquid with Antibacterial Peptide Melittin: An Efficient Combination against Bacterial Cells

Growing antibiotic resistance has become a major health problem and has encouraged many researchers to find an alternative class of antibiotics. Combination therapy (covalent/noncovalent) is supposed to increase antibacterial activity leading to a decrease in administration dosage, thus lowering the risk of adverse side effects. The covalent coupling sometimes leads to instability and loss in the structure of AMPs. Therefore, herein, we have reported innovative research involving the noncovalent coupling of melittin (MEL), an antimicrobial peptide with a series of synthesized less toxic pyrrolidinium-based ionic liquids (ILs) for which MTT assay was performed. The antibacterial results of conjugates showed remarkable improvement in the MIC value as compared to MEL and ILs alone against Escherichia coli and Staphylococcus aureus . In addition, hemocompatibility results suggested good selectivity of the noncovalent conjugate as a potential antibiotic agent. Further, the docking study was employed to acquire the most favorable conformation of MEL in the presence of ILs. The best possible complex was further studied using various spectroscopic techniques, which showed appreciable binding and stability of the complex.

Structure-Activity Relationship of Peptide-Conjugated Chloramphenicol for Inhibiting Escherichia coli

Intravenous administration of a prodrug, chloramphenicol succinate (CLsu), is ineffective. Recently, we have shown that conjugation of diglycine of CLsu (CLsuGG) not only increases the antibiotic efficacy against Escherichia coli but also reduces adverse drug effects against bone marrow stromal cells. Here, we report the synthesis of structural analogues of CLsuGG and their activities against E. coli. These analogues reveal several trends: (i) except the water-insoluble analogues, the attachment of peptides to CLsu enhances the efficacy of the prodrugs; (ii) negative charges, high steric hindrance in the side chains, or a rigid diester decreases the activities of prodrugs in comparison to CLsuGG; (iii) dipeptides apparently increase the efficacy of the prodrugs most effectively; and so forth. This work suggests that conjugating peptides to CLsu effectively modulates the properties of prodrugs. The structure-activity relationship of these new conjugates may provide useful insights for expanding the pool of antibiotics.

Conjugation of Cell-Penetrating Peptides to Antimicrobial Peptides Enhances Antibacterial Activity

Antimicrobial peptides (AMPs), essential elements in host innate immune defenses against numerous pathogens, have received considerable attention as potential alternatives to conventional antibiotics. Most AMPs exert broad-spectrum antimicrobial activity through depolarization and permeabilization of the bacterial cytoplasmic membrane. Here, we introduce a new approach for enhancing the antibiotic activity of AMPs by conjugation of a cationic cell-penetrating peptide (CPP). Interestingly, CPP-conjugated AMPs elicited only a 2- to 4-fold increase in antimicrobial activity against Gram-positive bacteria, but showed a 4- to 16-fold increase in antimicrobial activity against Gram-negative bacteria. Although CPP-AMP conjugates did not significantly increase membrane permeability, they efficiently translocated across a lipid bilayer. Indeed, confocal microscopy showed that, while AMPs were localized mainly in the membrane of Escherichia coli, the conjugates readily penetrated bacterial cells. In addition, the conjugates exhibited a higher affinity for DNA than unconjugated AMPs. Collectively, we demonstrate that CPP-AMP conjugates possess multiple functional properties, including membrane permeabilization, membrane translocation, and DNA binding, which are involved in their enhanced antibacterial activity against Gram-negative bacteria. We propose that conjugation of CPPs to AMPs may present an effective approach for the development of novel antimicrobials against Gram-negative bacteria.

Drug delivery systems designed to overcome antimicrobial resistance

Antimicrobial resistance has emerged as a huge challenge to the effective treatment of infectious diseases. Aside from a modest number of novel anti-infective agents, very few new classes of antibiotics have been successfully developed for therapeutic use. Despite the research efforts of numerous scientists, the fight against antimicrobial (ATB) resistance has been a longstanding continued effort, as pathogens rapidly adapt and evolve through various strategies, to escape the action of ATBs. Among other mechanisms of resistance to antibiotics, the sophisticated envelopes surrounding microbes especially form a major barrier for almost all anti-infective agents. In addition, the mammalian cell membrane presents another obstacle to the ATBs that target intracellular pathogens. To negotiate these biological membranes, scientists have developed drug delivery systems to help drugs traverse the cell wall; these are called "Trojan horse" strategies. Within these delivery systems, ATB molecules can be conjugated with one of many different types of carriers. These carriers could include any of the following: siderophores, antimicrobial peptides, cell-penetrating peptides, antibodies, or even nanoparticles. In recent years, the Trojan horse-inspired delivery systems have been increasingly reported as efficient strategies to expand the arsenal of therapeutic solutions and/or reinforce the effectiveness of conventional ATBs against drug-resistant microbes, while also minimizing the side effects of these drugs. In this paper, we aim to review and report on the recent progress made in these newly prevalent ATB delivery strategies, within the current context of increasing ATB resistance.

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.