The value of antimicrobial peptides in the age of resistance

A completely bio-based corn starch/sodium carboxymethyl cellulose film with antibacterial and antioxidant performance modified by a natural alcohol ester of amino acid and curcumin

To address the ecological pollution caused by synthetic antimicrobial agents in conventional food packaging films, we have successfully developed a fully bio-based and sustainable food packaging film that exhibits exceptional antibacterial and antioxidant properties. In this study, we designed and synthesized two novel natural alcohol esters of amino acid (NAEAAs)-L-Trp-Men and L-Trp-Bor-through esterification reactions involving L-tryptophan (L-Trp) and L-Menthol or Borneol, respectively. A multifunctional composite film system was constructed using natural corn starch (CS) and sodium carboxymethyl cellulose (CMC) as the matrix materials, with NAEAAs serving as the antimicrobial active components and curcumin (Cur) as the antioxidant. Experimental results demonstrated that the CS/CMC/Men2/Cur2 composite film, containing 2 wt% additives, exhibited nearly complete (≈100 %) broad-spectrum antibacterial efficiency against both Escherichia coli and Staphylococcus aureus, alongside a DPPH radical scavenging rate of 45.69 ± 1.39 %. Cytotoxicity tests confirmed the excellent biocompatibility of NAEAAs, which hydrolyze into amino acids and natural alcohols, thereby minimizing environmental contamination. These fully natural material-based films present a novel approach for developing green, pollution-free, and renewable bio-based food packaging materials.

PMAP-37: A versatile cathelicidin for neutralizing bacteria and viruses

Antimicrobial peptides (AMPs), such as cathelicidins, show dual functionality by directly combating pathogens and indirectly eliminating them through stimulation of the immune system, generating interest in their therapeutic potential. Pigs have a large set of 11 cathelicidins, of which PMAP-37 is relatively understudied compared to some of the better-known cathelicidins. This study describes the effectiveness of PMAP-37 against both bacteria and viruses. PMAP-37 exhibited potent in vitro antimicrobial activity against both Gram-positive (Bacillus globigii) and Gram-negative bacteria (Escherichia coli) with minimum bactericidal concentrations (MBCs) of 2.5 and 5 μM, respectively. PMAP-37 caused a rapid permeabilization of E. coli's outer and inner membranes within 5 min, indicating its efficacy in disrupting bacterial cell membranes. Furthermore, PMAP-37 neutralized nitric oxide production in a macrophage cell line stimulated with various forms of LPS, Lipid A, or LTA in a dose-dependent manner. Flow cytometric analysis confirmed PMAP-37's capacity to inhibit LPS binding to macrophages, while zeta potential analysis showed the peptide's capacity to neutralize the negative charge of both the E. coli membrane and LPS micellular surfaces. Interestingly, PMAP-37 also exhibited antiviral activity against an important porcine pathogen, the porcine epidemic diarrhea virus (PEDV). These findings underscore the multifunctional properties of PMAP-37, and provide potential leads for future therapeutic use within the pig industry.

Antibacterial activity of the novel peptide Pac-525 with the RGD motif against intracellular Escherichia coli

Infections caused by invasive intracellular bacteria pose major therapeutic challenges due to pathogen survival and growth inside of host cells as well as the low intracellular accessibility for conventional antibiotics. The limited ability of most antibiotics to enter intracellular compartments underscores the urgent need for innovative antimicrobial agents capable of overcoming these barriers. In this study, the antibacterial peptide Pac525 was synthesized with the RGD domain to facilitate efficient penetration into eukaryotic cells. The efficacy and safety of RGD-Pac525 was evaluated in intracellular infection models, using the macrophage cell line RAW 264.7, chicken intestinal organoids, and chicken embryo tissues via the chorioallantoic membrane (CAM). Our findings from cell line experiments demonstrate that the RGD-Pac525 peptide retained the antimicrobial properties of the original peptide without compromising its efficacy. While RGD-Pac525 reduced the intracellular adherent-invasive pathogen Escherichia coli KV203 by 50% in RAW 264.7 macrophage cells, it did not adversely affect the macrophage viability. Additionally, RGD-Pac525 effectively reduced the intracellular bacterial burden in organoids, without compromising their structural integrity. In ovo bioassays, a substantial reduction in the bacterial load was observed in liver and intestinal tissues, indicating the peptide ability to achieve systemic distribution and to overcome tissue barriers. RGD-Pac525 was effective in infection models by suppressing bacterial growth. Preliminary observations suggest it may also affect host responses, indicating a potential for combined antimicrobial and therapeutic effects that warrant further studies. This study provides a compelling proof of concept for utilizing RGD-modified antimicrobial peptides for treatment of intracellular bacterial infections.

Design, synthesis and evaluation of lysine- and leucine-rich hydrocarbon-stapled peptides as antibacterial agents

To address the challenge of antimicrobial resistance, we investigated new antibacterial peptides based on lysine- and leucine-rich sequences. We stabilised their membrane-active secondary structures by applying hydrocarbon stapling at sequence positions i and i+4. Stapling improved peptide structural stability in both aqueous and lipid environments, regardless of the staple position. It also enhanced antibacterial efficiency against both gram-negative and gram-positive bacteria, including antibiotic-resistant strains, with minimum inhibitory concentrations (MICs) of 2-4 μM (2.5-5.5 μg/mL). The stapled peptides showed increased resistance to enzymatic degradation, particularly with staples incorporated near the N-terminus, and were not haemolytic or cytotoxic at their MICs. Molecular dynamics simulations revealed how stapling aids in (i) stabilising the membrane-active secondary structure of amphipathic peptides and (ii) accelerating their membrane insertion. Our results provide insight into peptide design for antimicrobial use. We show that hydrocarbon stapling of lysine- and leucine-rich short sequences may offer a pathway towards more stable and effective antibacterial agents.

Antimicrobial Peptide-Peptoid Macrocycles from the Polymyxin B2 Chemical Space

Macrocycles have emerged as important new modalities in drug discovery. In the context of addressing the global threat of antimicrobial resistance, here we used a genetic algorithm as a computational tool to evolve peptide-peptoid macrocycles to resemble polymyxin B2 (PMB2), a macrocyclic lipopeptide natural product used as last resort antibiotic. Synthesis and testing of 41 PMB2 analogs revealed several peptide-peptoid macrocycles showing strong, although salt sensitive, activity against Escherichia coli and multidrug-resistant strains of Pseudomonas aeruginosa, high serum stability, and lower toxicity to kidney cells compared to PMB2. These macrocycles resembled PMB2 in terms of outer membrane permeabilization, inner membrane depolarization, lipopolysaccharide binding, and loss of activity when linearized, but, unlike PMB2, induced aggregation of intracellular contents, an effect was reported for other antimicrobial peptoids. These experiments exemplify a combined computational and experimental approach which might be generally useful to explore the chemical space of macrocyclic peptide natural products.

A novel antimicrobial peptide Larimicin78-102 from large yellow croaker (Larimichthys crocea) shows potent antibacterial activity in vitro and enhances resistance to vibrio fluvialis infection in vivo

Antimicrobial peptides (AMPs) are considered a key component of innate immunity, playing a vital role in host defense. In the study, a novel functional gene, named Larimicin, was identified from large yellow croaker Larimichthys crocea. The Larimicin gene was widely distributed in multiple tissues of healthy L. crocea and was significantly induced in the liver after Vibrio alginolyticus or Vibrio parahaemolyticus infection. Larimicin78-102, a truncated peptide derived from Larimicin, showed broad-spectrum antimicrobial activity and a binding affinity with LPS. It exhibited effective bactericidal activity against the common aquatic pathogens Vibrio fluvialis, Pseudomonas fluorescens, and Pseudomonas putida. It also showed anti-biofilm activity against three aquatic pathogens. Moreover, Larimicin78-102 disrupted the integrity of the outer and inner membranes, resulting in ATP leakage and intracellular ROS accumulation, which ultimately led to bacterial cell death. Larimicin78-102 exhibited good thermal stability and cation tolerance, with no obvious cytotoxicity or hemolytic activity. Notably, Larimicin78-102 significantly improved the survival rate of L. crocea infected with V. fluvialis, raising it to 95 %, indicating its anti-infective role in vivo. In addition, Larimicin78-102 significantly reduced the expression of the pro-inflammatory cytokines TNF-α and IL-1β, while up-regulating the anti-inflammatory factor IL-4 mRNA level. It also elevated the expression levels of piscidin, hepcidin, and lysozyme, as well as enhanced the enzymatic activity of lysozyme. Taken together, Larimicin78-102 is a potential antibacterial agent for use in aquaculture to combat V. fluvialis infection diseases in the future.

Lipidized LL37-loaded PLGA nanocarriers: Bioengineered peptide delivery systems for enhanced wound healing

Antimicrobial peptides (AMPs) such as LL37 offer a promising alternative to conventional antibiotics in treating chronic and multidrug-resistant wound infections. However, their clinical translation is limited by rapid degradation and cytotoxicity at high concentrations. This study investigates the encapsulation of a palmitoylated LL37 in a FDA-approved poly(lactic-co-glycolic acid) (PLGA) nanoparticles using two fabrication techniques, nanoprecipitation and microfluidics, to enhance stability and controlled peptide release. Microfluidic-generated nanoparticles demonstrated superior size uniformity, smaller hydrodynamic size (102.3 ± 2.0 nm vs 189.3 ± 3.4 nm), improved stability, and prolonged LL37(P) release compared to nanoparticles obtained via bulk nanoprecipitation method. LL37-encapsulated nanoparticles demonstrated controlled peptide release, enhanced keratinocyte uptake, and significant fibroblast-mediated wound closure acceleration. Proteomic analysis of the nanoparticle-protein corona revealed enrichment in proteins involved in coagulation, inflammation modulation, and extracellular matrix remodelling, suggesting an active role of nanoparticles in modulating the wound healing microenvironment. These findings highlight PLGA-based LL37 loaded nanocarriers as a promising biopolymer platform for AMP delivery in wound healing applications and as a viable therapeutic strategy in regenerative medicine and infection control.

3D-Printed cannabidiol stent for local treatment of urinary tract infections

Urinary tract infections (UTIs) are highly prevalent among women and those assigned female at birth, and frequently necessitate the administration of systemic antibiotics, which contributes to the antibiotic resistance crisis due to overuse and suboptimal patient adherence. This study introduces an innovative 3D-printed stent designed specifically for the localized treatment of UTIs, aiming at reducing systemic drug exposure and lowering recurrence rates. Tailored for the female urethra, the stent consists of a laponite-alginate hydrogel scaffold integrated with cannabidiol (CBD)-loaded PLGA microparticles to facilitate controlled drug release. A design of experiments (DoE) approach was utilized to optimize printing parameters, ensuring structural integrity and printability. CBD, known for its analgesic and antimicrobial properties, was added as therapeutic agent. The composite system exhibited prolonged antimicrobial activity against both Gram-positive and Gram-negative bacteria. This localized strategy has the potential to enhance therapeutic effects while reducing the need for systemic administration, which may, in turn, help limit associated side effects and improve patient adherence. The integration of 3D printing technology and controlled drug release signifies a substantial advancement towards more effective and personalized interventions for UTI management.

Prediction of Chemically Modified Antimicrobial Peptides and Their Sub-functional Activities Using Hybrid Features

Antimicrobial peptides (AMPs) demonstrate a broad spectrum of activities against various pathogens, thereby offering a promising strategy to mitigate the urgent challenge of antimicrobial resistance. Recent studies indicate that chemically modified AMPs (cmAMPs), which contain chemically modified amino acids, have the potential to alleviate the adverse effects commonly associated with conventional AMPs. Nevertheless, there remains a notable deficiency in computational methods specifically designed for the analysis and prediction of cmAMPs and their sub-function predictions. In this study, we proposed a two-layer model, termed as iCMAMP, aimed for the identification of cmAMPs and their sub-functional activities. The first layer, referred to as iCMAMP-1L, integrates three categories encompassing seven distinct groups of features, in conjunction with an ensemble method designed at enhancing predictive accuracy for cmAMPs. This ensemble approach effectively extracts relevant insights from a heterogeneous array of features sets while addressing potential dimensionality challenges. On the test dataset, iCMAMP-1L achieved an ACC of 0.934 and an MCC of 0.868, representing improvements of 3.4% and 6.8%, respectively, over AntiMPmod, which is the sole existing method for predicting cmAMPs. A comparative analysis between cmAMPs and their corresponding AMPs revealed that chemical modifications can significantly reduce hemolysis and toxicity associated with AMPs, while the functional characteristics of the peptides are primarily determined by their sequences. The second layer of our model, designated as iCMAMP-2L, employed a multi-label classification approach to predict the sub-functional activities of cmAMPs, with a specific focus on the dipeptide composition-based features. On the test dataset, iCMAMP-2L achieved an Accuracy of 0.390 and an Absolute true of 0.621. The data and Python code used in the iCMAMP model are available at https://github.com/swicher123/iCMAMP/tree/master .

Host-Guest Antimicrobial Based on Conjugated Oligoelectrolyte and Cyclodextrin

The escalating global threat of antimicrobial resistance necessitates the development of new antimicrobial agents. In this study, we prepared a resveratrol-derived antimicrobial conjugated oligoelectrolyte (COE) named DY6 to enhance drug-like properties. While DY6's increased hydrophobicity augmented its antibacterial efficacy, it also induced significant cytotoxicity, highlighting the long-existing dilemma of amphiphilic antimicrobials. To mitigate this issue, we employed a supramolecular strategy by complexing DY6 with sodium sulfobutyl ether β-cyclodextrin (SβCD), forming the host-guest inclusion complex DY6@SβCD. This complex elevated the half-maximal inhibitory concentration (IC50) against L929 cells from 9.4 to over 128 µg mL-1 while maintaining a minimum inhibitory concentration (MIC) of 2 µg mL-1 against methicillin-resistant Staphylococcus aureus (MRSA). NMR and UV-vis spectroscopic analyses confirmed that DY6's aromatic backbone is encapsulated within the hydrophobic cavity of SβCD. Isothermal titration calorimetry revealed that size compatibility and electrostatic interactions are essential for stable complex formation and enhanced biocompatibility. Importantly, DY6@SβCD exhibited no resistance development over 14-day serial passages against S. aureus, significantly outperforming norfloxacin. In biofilm-based MRSA-infected wound and corneal models, DY6@SβCD more effectively reduced bacterial load and inflammation compared to the last-resort antibiotic vancomycin. These findings demonstrate the potential utility of supramolecular host-guest approach based on COEs to overcome the drug-resistant challenges.

Improve the Stability and Activity of Antimicrobial Peptides by the Proline-Based PXXP Hinge Structure

Developing a simple and effective strategy to enhance the stability of antimicrobial peptides (AMPs) is critical for successful AMP design. In this study, we leveraged the property of proline to form hinge-like structures and designed a series of repetitive symmetrical sequence AMPs with different proline-based hinge centers (PWWP, PKKP, and PWKP), proposing a template of (KW)nPXXP(WK)n-NH2 (where XX = WW, n = 1-4 or XX = KK, WK, n = 2-4). The corresponding templates without hinge structures, (KW)n(WK)n-NH2 (n = 1-4), were used as controls. Through comprehensive evaluations of activity, toxicity, and stability, we identified two promising AMP candidates, (KW)3PK and (KW)3PWK, which demonstrated excellent antibacterial activity, cell selectivity, and stability. Our findings indicate that incorporating a proline-containing PXXP hinge structure into AMP sequences could serve as an effective strategy to enhance AMP stability.

Tutorial: guidelines for the use of machine learning methods to mine genomes and proteomes for antibiotic discovery

Genomes and proteomes constitute a rich reservoir of molecular diversity. However, they have remained underexplored because of a lack of appropriate tools. In recent years, computational approaches have been developed to mine this unexplored biological information, or dark matter, accelerating the discovery of new antibiotic molecules. Such efforts have yielded a wide range of new molecules. These include peptides released via predicted proteolytic cleavage of larger proteins, termed 'encrypted peptides', which have been found to be widespread in nature. Molecules encoded by and translated from small open reading frames within genomic sequences have also been uncovered, further expanding the landscape of bioactive compounds. Here, we discuss computational approaches, including machine learning and artificial intelligence (AI) tools, which have been used to date to identify antimicrobial compounds, with a special emphasis on peptides. We also propose potential avenues for future exploration in this rapidly evolving field. Moreover, we provide an overview of the experimental methods commonly used to validate these computational predictions. We anticipate that efforts combining cutting-edge AI and experimental approaches for biological sequence mining will reveal new insights into host immunity and continue to accelerate discoveries in the fields of antibiotics and infectious diseases.

Revolutionizing agroindustry: Towards the industrial application of antimicrobial peptides against pathogens and pests

Antibiotics are essential chemicals for medicine and agritech. However, all antibiotics are small molecules that pathogens evolve antimicrobial resistance (AMR). Alternatively, antimicrobial peptides (AMPs) offer potential to overcome or evade AMR. AMPs provide broad-spectrum activity, favourable biosafety profiles, and a rapid and efficient mechanism of action with low resistance incidence. These properties have driven innovative applications, positioning AMPs as promising contributors to advancements in various industrial sectors. This review evaluates the multifaceted nature of AMPs and their biotechnological applications in underexplored sectors. In the food industry, the application of AMPs helps to suppress the growth of microorganisms, thereby decreasing foodborne illnesses, minimizing food waste, and prolonging the shelf life of products. In animal husbandry and aquaculture, incorporating AMPs into the diet reduces the load of pathogenic microorganisms and enhances growth performance and survival rates. In agriculture, AMPs provide an alternative to decrease the use of chemical pesticides and antibiotics. We also review current methods for obtaining AMPs, including chemical synthesis, recombinant DNA technology, cell-free protein synthesis, and molecular farming, are also reviewed. Finally, we look to the peptide market to assess its status, progress, and transition from the discovery stage to benefits for society and high-quality products. Overall, our review exemplifies the other side of the coin of AMPs and how these molecules provide similar benefits to conventional antibiotics and pesticides in the agritech sector.

Reducing Functional Domain of Histatin 5 Improves Antifungal Activity and Prevents Proteolytic Degradation

Histatin 5 (Hst5) is an antifungal peptide (AFP) naturally produced by parotid glands with strong activity against Candida albicans. One of its mechanisms of action is the generation of reactive oxygen species (ROS) inside the C. albicans cells. Despite being an important peptide for the human innate immune response, its activity is reduced or inactivated by proteolytic degradation caused by salivary enzymes. To overcome this barrier, we used solid phase peptide synthesis (SPPS) to modify the Hst5 amino acid sequence improving its antifungal action and minimizing its degradation. We synthesized five peptides, three of which were based on the Hst5 functional domain. We determined that the smallest peptides (8WH5, 7WH5 and 6WH5) demonstrated the greatest antifungal action against C. albicans, including one fluconazole-resistant strain. Besides that, cationic-PAGE and HPLC assays showed that the degradation in saliva was slower for the smaller peptides than for 0WHst5 and WP113. Furthermore, 8WH5, 7WH5 and 6WH5 were found in the samples even after 8 h in whole saliva, while 0WHst5 and WP113 completely disappear after 1.5 h. Finally, we found that the smaller peptides were less fragmented than the 0WHst5 and WP113, so they were the smallest fragments of Hst5 to preserve its antifungal action with reduced degradation in whole saliva. Thus, they can be considered promising molecules for the treatment of C. albicans in the oral cavity.

Dodecapeptides derived from human cathelicidin with potent activity against carbapenem-resistant Acinetobacter baumannii

The increasing infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) poses a serious threat to global public health. Antimicrobial peptides (AMPs) are alternatives to conventional antibiotics in combating superbugs. However, discovering AMPs with low synthesis costs and strong antibacterial effects against CRAB is challenging. In this study, we synthesized 28 dodecapeptides for bactericidal assessment by site mutation and all-hydrocarbon stapling on the basis of the antibacterial core of human cathelicidin. The linear derivative d12 (Q5RD9I-KR12) and the i, i + 4 stapled peptide d24, which was generated by substituting Val4 and Lys8 of d12 to staples, stood out among the candidates. These short AMPs efficiently bound to bacterial membrane and penetrated it in a lipid A-dependent manner, resulting in low minimal inhibitory concentrations to inactivate CRAB clinical isolates (2.5-20 μg/mL). The CRAB infection mouse models of irradiation-assisted local pulmonary infection and intra-abdominal sepsis revealed that treatment with d12 and d24 significantly eliminated CRAB in vivo and thereby increased mouse survival. Owing to its improved proteolytic resistance, d24 outperformed d12 in suppressing intra-abdominal CRAB infection. The excellent antibacterial effects, good biocompatibility, and facile synthesis make d12 and d24 promising candidates to curb CRAB infections in different application scenarios.

Naturally inspired chimeric quinolone derivatives to reverse bacterial drug resistance

Antimicrobial resistance poses an urgent threat to global health, underscoring the critical need for new antibacterial drugs. Ciprofloxacin, a third-generation quinolone antibiotic, is used to treat different types of bacterial infections; however, it often results in the rapid emergence of resistance in clinical settings. Inspired by low susceptibility to antimicrobial resistance of natural antimicrobial peptides, we herein propose a host defense peptide-mimicking strategy for designing chimeric quinolone derivatives which may reduce the likelihood of antibacterial resistance. This strategy involves the incorporation of deliberately designed amphiphilic moieties into ciprofloxacin to mimic the structural characteristics and resistance-evading properties of host defense peptides. A resulting chimeric compound IPMCL-28b, carrying a rigid linker and three cationic amino acids along with a lipophilic acyl n-decanoyl tail, exhibited potent activity against a panel of multidrug-resistant bacterial strains by endowing the ciprofloxacin derivatives with additional ability to disrupt bacterial cell membranes. Molecular dynamics simulations showed that IPMCL-28b demonstrates significantly stronger disruptive interactions with cell membranes than ciprofloxacin. This compound not only demonstrated high selectivity with low hemolysis side effect, but also significantly reduced the likelihood of resistance development compared with ciprofloxacin. Excitingly, IPMCL-28b demonstrated highly enhanced in vivo antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) with a 99.99 % (4.4 log) reduction in skin bacterial load after a single dose. These findings highlight the potential of host defense peptides-mimicking amphiphilic ciprofloxacin derivatives to reverse antibiotic resistance and mitigate the development of antimicrobial resistance.

Molecular dynamics study of the helix-to-disorder transition in short antimicrobial peptides from Urodacus yaschenkoi

The bioactivity of the short antimicrobial peptides (ssAMPs) UyCT1, CT2, CT3, CT5, Uy17, Uy192, and Uy234 from the scorpion Urodacus yaschenkoi has been well-characterized. The antagonistic effect reported in those studies on some clinical isolates of pathogenic bacteria, including Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli was studied with an in silico approach to contrast their bioactivity in molecular terms. The peptides were modeled by generating high-quality structures with AlphaFold2, properly validated, and subjected to dynamic simulations in aqueous systems with the Gromos 43a1 and Charmm 36 force fields. Our analysis indicates that the degree of helicity of these peptides is closely linked to their composition and several physicochemical factors such as the hydrophobicity index, electrostatic potential, intrinsic flexibility, and dipole moment. We also found interesting parallels between the degree of order mentioned and the potency of each peptide with previously studied bacterial strains, specifically S. aureus. We analyzed in more detail of two specific peptides, UyCT1 and UyCT2, whose sequences are almost identical, except for the presence of a G-cap in the former. This subtle difference has a decisive impact on the conformational dynamics of these peptides, making the UyCT2 peptide more prone to disorder and the UyCT1 peptide more stable through the formation of multiple H-bonds. This analysis, based on an exhaustive characterization of the physicochemical properties of these ssAMPs, together with the determination of their conformational dynamics and the correlation with experimental data, could be the basis for the design and optimization of new drugs based on natural peptides found in scorpion venoms.

Isolation, purification and identification of antibacterial peptides from Jinhua ham broth and molecular simulation analyses of their interaction with bacterial porins

The bioactive peptides in Jinhua ham could be released into the broth during cooking. After comparing peptide antibacterial activity from Jinhua ham broth with varying cooking durations, the cooking-2-h broths were selected for further analysis using cation-exchange and reverse-phase-liquid chromatography. The purified peptide sequences were subsequently synthesized and tested for their antibacterial activity. Four peptides (IKKVVKQASEGP, LGRVPRGKKKL, LKGGKKQLQKL, and MDAIKKKMQMLK) were identified with IC50 values for S. typhimurium and S. aureus below 0.4 mg/mL. Molecular docking and dynamics simulations were employed to investigate the interaction between the four antibacterial peptides and the outer membrane protein F (Omp F) of the Salmonella membrane. All four peptides demonstrated binding energies with Omp F lower than -7 kcal/mol. Stability indicators in molecular dynamics showed minimal fluctuations, further confirming the compactness and stability of the peptide-Omp F complexes. Notably, all four peptides altered the conformation of Omp F, thereby enhancing cell membrane permeability.

Autocrine peptides inhibited the formation of VBNC state of Staphylococcus aureus

Viable but non-culturable (VBNC) Staphylococcus aureus cannot form colonies on a medium, causing a false negative result in culture-based detection, which is a potential hazard to human health. In this study, four peptides (PVSS.a-1, PVSS.a-2, PVSS.a-3, and PVSS.a-4) were identified in the suspension of S. aureus during the VBNC state induction. Notably, PVSS.a-1 and PVSS.a-2 prolonged the entry of S. aureus into the VBNC state in citric acid solution (pH 4.0) at 4℃ by 83 % and 103 %, respectively. Such a delaying effect indicates that S. aureus might be forced to enter the VBNC state under pressure, rather than actively. Microscopic observation and zeta-potential determination suggested that PVSS.a-1 and PVSS.a-2 improved the aggregation of S. aureus cells. Furthermore, the two peptides were demonstrated to enter cells by FITC-label localization detection, and changed internal structures and improved intracellular enzyme activities occurred in the two peptide-treated cells. Through the analysis of interactions with DNA and proteins of S. aureus, it was found that PVSS.a-1 and PVSS.a-2 might affect cellular processes, including cell division, transcription, translation, and material and energy metabolisms. These alterations improved the viability and culturability of S. aureus, thereby delaying VBNC formation. In summary, our study reveals how autocrine peptides delay VBNC formation of S. aureus, and provides a new insight into the real intention of bacteria to form VBNC state under adverse conditions.

Discovery and Optimisation of Novel Bombinin-Derived Peptides from Bombina variegata against Staphylococcus aureus

Amphibian skin-secreted antimicrobial peptides (AMPs) have garnered significant attention for their excellent biological activity and low propensity for drug resistance over the past 40 years. Bombinins and bombinin H, two classes of AMPs isolated from the skin secretions of Bombina species, demonstrate strong antimicrobial activity against broad-spectrum microorganisms. In this study, two novel peptides, bombinin-like peptide 7S and bombinin-H2L, were identified from the toad, Bombina variegata. While both peptides exhibited broad-spectrum antimicrobial activity, they also showed relatively high cytotoxicity. To explore the structure-activity relationship and enhance therapeutic potential, bombinin-H2L, which displayed stronger average antimicrobial activity, was used as a template. With the aid of bioinformatics analysis, a series of bombinin-H2L analogues were designed by increasing the net positive charges and/or adjusting the amphiphilicity of the parent peptide. Among these analogues, [Arg8, 15]BH2L and [Lys7, 8]BH2L demonstrated high therapeutic efficacy and specificity toward clinically isolated, drug-resistant Staphylococcus aureus strains in both in vitro and ex vivo tests. Their notable biosafety profiles, sensitivity to diverse environments, and ability to disrupt biofilms highlight their potential for further development. Additionally, studies on the mechanism of [Arg8, 15]BH2L and [Lys7, 8]BH2L revealed a membrane-targeted antimicrobial mechanism, with its antibacterial function exerted by disrupting the integrity of bacterial membranes. These findings provide valuable insights into structural modifications of bombinin H peptides for enhanced activity, and [Arg8, 15]BH2L and [Lys7, 8]BH2L have the potential as promising candidates for novel antibacterial agents in treated bacterial skin infections.

Design and synthesis of tetrahydrochromeno[3,4-e]isoindole-1,3(2H,3aH)-dione derivatives via the Diels-Alder reaction: molecular docking, antibacterial activity, ADMET analysis and photophysical properties

A series of fused tetrahydrochromeno[3,4-e]isoindole-1,3(2H,3aH)-dione derivatives was successfully synthesized via the Diels-Alder reaction. Molecular docking studies were conducted to understand the interaction modes between the synthesized hybrid compounds and the receptor bacterial strains of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Notably, the in silico results demonstrated that compound 19l (-8.7 kcal mol-1 with E. coli and -8.4 kcal mol-1 with S. aureus) and 19p (-8.7 kcal mol-1 with E. coli and -9.1 kcal mol-1 with S. aureus) exhibited good binding values. Additionally, the in vitro antibacterial studies showed that compounds 19l and 19p demonstrated excellent antibacterial activities, with a zone of inhibition (ZI) of 17 mm and a minimum inhibitory concentration (MIC) of 12.5 μg mL-1 against both E. coli and S. aureus, which were comparable to the performance of the standard antibiotic ciprofloxacin. Further, the bioavailability was assessed through virtual ADMET parameters, which suggested that most of the compounds possessed favorable pharmacokinetic profiles. To further enrich the study, photophysical properties of all the synthesized molecules were also examined using UV-visible and fluorescent spectroscopies.

Medical Potential of Insect Symbionts

Insect symbionts and their metabolites are complex and diverse and are gradually becoming an important source of new medical materials. Some culturable symbionts from insects produce a variety of active compounds with medical potential. Among them, fatty acids, antibacterial peptides, polyene macrolides, alkaloids, and roseoflavin can inhibit the growth of human pathogenic bacteria and fungi; lipases, yeast killer toxins, reactive oxygen species, pyridines, polyethers, macrotetrolide nactins, and macrolides can kill human parasites; and peptides and polyketides can inhibit human tumors. However, due to difficulty in the culture of symbionts in vitro, difficulty in targeting bacteria to specific sites in the human body, the limited capability of symbionts to produce active metabolites in vitro, inconsistent clinical research results, adverse reactions on humans, and the development of antibiotic resistance, the application of insect symbionts and their metabolites in the medical field remains in its infancy. This paper summarizes the medical potential of insect symbionts and their metabolites and analyzes the status quo and existing problems with their medical application. Possible solutions to these problems are also proposed, with the aim of hastening the utilization of insect symbionts and their metabolites in the medical field.

Combination of antimicrobial peptide and clinical antibiotic shows enhanced potency toward Acinetobacter baumannii infection

The continued development of novel antimicrobial treatment strategies is crucial for maintaining an effective therapeutic arsenal, and antimicrobial peptides (AMPs) exhibit promising activities against a wide range of pathogens. In this study, we tested the combined effects of an AMP, TP4-3, and meropenem on Acinetobacter baumannii, which is responsible for many severe infections and is associated with high rates of overall mortality and morbidity. This study aimed to develop an effective combination therapy for microbial infections. TP4-3 and meropenem were found to act synergistically toward Acinetobacter baumannii and exhibit an activity profile better than those of the individual compounds. TP4-3 is an antimicrobial peptide with proven activity, low toxicity and extended stability. This AMP was combined with meropenem and tested for efficacy against A. baumannii using a panel of in vitro and in vivo tests. The combination of TP4-3 and meropenem exhibited robust activity against Acinetobacter baumannii pathogens. In particular, the combined treatment demonstrated significant antibiofilm properties and a lower degree of induced resistance than meropenem alone. Additionally, the combination showed an excellent activity profile in in vivo studies. Thus, the combination of TP4-3 and meropenem appears to be an effective strategy to mitigate the detrimental consequences of infections caused by this clinically relevant pathogen. Since the combination of TP4-3 and meropenem displayed better activity than the individual compounds, this strategy of combining AMPs with clinical antibiotics may be suitable for development of clinical treatments targeting various microbial infections.

HMAMP: Designing Highly Potent Antimicrobial Peptides Using a Hypervolume-Driven Multiobjective Deep Generative Model

Antimicrobial peptides (AMPs) have exhibited unprecedented potential as biomaterials in combating multidrug-resistant bacteria, prompting the proposal of many excellent generative models. However, the multiobjective nature of AMP discovery is often overlooked, contributing to the high attrition rate of drug candidates. Here, we propose a novel approach termed hypervolume-driven multiobjective AMP design (HMAMP), which prioritizes the simultaneous optimization of multiattribute AMPs. By synergizing reinforcement learning and a gradient descent algorithm rooted in the hypervolume maximization concept, HMAMP effectively biases generative processes and mitigates the pattern collapse issue. Comparative experiments show that HMAMP significantly outperforms state-of-the-art methods in effectiveness and diversity. A knee-based decision strategy is then employed to fast screen candidates with favorable physicochemical properties, aligning with the enhanced antimicrobial activity and reduced side effects. Molecular visualization further elucidates structural and functional properties of the AMPs. Overall, HMAMP is an effective approach to traverse large and complex exploration spaces to search for idealism-realism trade-off AMPs.

Potent antimicrobial activity of hydrogel loaded with the antimicrobial peptide, D-Bac8c2,5 Leu, against monospecies and polymicrobial biofilms of Staphylococcus aureus and Pseudomonas aeruginosa

Introduction

Acute and chronic wound infections involving biofilms and caused by antimicrobial resistant (AMR) pathogens present significant challenges in healthcare, leading to substantial patient morbidity, increased hospital stays, and rising healthcare costs. Novel antimicrobial therapies are urgently needed to address these infections.

Methods

A screening of multiple antimicrobial peptides (AMPs) was performed and the most potent candidate, D-Bac8c2,5 Leu, was tested against monospecies and polymicrobial biofilms of Staphylococcus aureus and Pseudomonas aeruginosa using static and dynamic in vitro models. Cytotoxicity was evaluated on human cell lines, and the peptide was incorporated into a methylcellulose hydrogel to assess sustained release and antimicrobial efficacy as a hydrogel dressing.

Results

D-Bac8c2,5 Leu significantly reduced biofilm viability in both monospecies and polymicrobial biofilms. In static biofilm assays, treatment led to a 2-3 log reduction in bacterial load compared to untreated controls. In Duckworth biofilm flow device, a similar reduction was observed, demonstrating efficacy in conditions mimicking wound environments. Furthermore, D-Bac8c2,5 Leu exhibited low cytotoxicity against human cell lines, and its incorporation into a methylcellulose hydrogel facilitated sustained release and enhanced antimicrobial activity. Furthermore, the peptide-loaded hydrogel showed considerable efficacy in disrupting pre-formed biofilms, underscoring its potential as a novel treatment for acute and chronic wound infections.

Discussion

These findings highlight the potential of D-Bac8c2,5 Leu to help address the urgent need for effective therapies against AMR pathogens and biofilm-associated wound infections. Further studies should focus on in vivo efficacy to optimize its therapeutic application in wound care.

Rational design of synthetic antimicrobial peptides based on the Escherichia coli ShoB toxin

Antibiotic resistance is an escalating global concern, necessitating the development of novel antibiotics with unique mechanisms of action, and preferably also with a lowered propensity for resistance development. Type-I Toxin-Antitoxin (TA) systems that are ubiquitous in bacterial genomes consist of a genetic toxin element encoding a hydrophobic peptide and an antitoxin element producing an sRNA that inhibits the toxin translation. Although the biological roles of these membrane-associated toxins remain incompletely understood, their inherent lethality upon overexpression suggests a potential as antimicrobial agents. In this study, we explore the ShoB toxin from the shoB-ohsC TA system in Escherichia coli (E. coli) as a basis for designing synthetic antimicrobial peptides for exogenous delivery. We demonstrate that ShoB-derived peptides can retain antimicrobial efficacy when modified into shorter, cationic analogs with enhanced solubility. Our most promising hits exhibit rapid bactericidal action and frequency of resistance within E. coli cultures indicate a limited tendency for resistance development. These findings highlight that type-I TA systems constitute a novel source of potential peptide-based antibiotics, thereby offering an alternative largely unexplored strategy to combat antibiotic-resistant bacterial infections.

Synthesis and Evaluation of Aquatic Antimicrobial Peptides Derived from Marine Metagenomes Using a High-Throughput Screening Approach

Bacterial diseases cause high mortality and considerable losses in aquaculture. The rapid expansion of intensive aquaculture has further increased the risk of large-scale outbreaks. However, the emergence of drug-resistant bacteria, food safety concerns, and environmental regulations have severely limited the availability of antimicrobial. Compared to traditional antibiotics, antimicrobial peptides (AMPs) offer broad spectrum activity, physicochemical stability, and lower resistance development. However, their low natural yield and high extraction costs along with the time-consuming and expensive nature of traditional drug discovery, pose a challenge. In this study, we applied a machine-learning macro-model to predict AMPs from three macrogenomes in the water column of South American white shrimp aquaculture ponds. The AMP content per megabase in the traditional earthen pond (TC1) was 1.8 times higher than in the biofloc pond (ZA1) and 63% higher than in the elevated pond (ZP11). A total of 1033 potential AMPs were predicted, including 6 anionic linear peptides, 616 cationic linear peptides, and 411 cationic cysteine-containing peptides. After screening based on structural, and physio-chemical properties, we selected 10 candidate peptides. Using a rapid high-throughput cell-free protein expression system, we identified nine peptides with antimicrobial activity against aquatic pathogens. Three were further validated through chemical synthesis. The three antimicrobial peptides (K-5, K-58, K-61) showed some inhibitory effects on all four pathogenic bacteria. The MIC of K-5 against Vibrio alginolyticus was 25 μM, the cell viability of the three peptides was higher than 70% at low concentrations (≤12.5 μM), and the hemolysis rate of K-5 and K-58 was lower than 5% at 200 μM. This study highlights the benefits of machine learning in AMP discovery, demonstrates the potential of cell-free protein synthesis systems for peptide screening, and provides an efficient method for high-throughput AMP identification for aquatic applications.

Antibiotic-Resistant Pseudomonas aeruginosa: Current Challenges and Emerging Alternative Therapies

Antibiotic-resistant Pseudomonas aeruginosa is a pathogen notorious for its resilience in clinical settings due to biofilm formation, efflux pumps, and the rapid acquisition of resistance genes. With traditional antibiotic therapy rendered ineffective against Pseudomonas aeruginosa infections, we explore alternative therapies that have shown promise, including antimicrobial peptides, nanoparticles and quorum sensing inhibitors. While these approaches offer potential, they each face challenges, such as specificity, stability, and delivery, which require careful consideration and further study. We also delve into emerging alternative strategies, such as bacteriophage therapy and CRISPR-Cas gene editing that could enhance targeted treatment for personalized medicine. As most of them are currently in experimental stages, we highlight the need for clinical trials and additional research to confirm their feasibility. Hence, we offer insights into new therapeutic avenues that could help address the pressing issue of antibiotic-resistant Pseudomonas aeruginosa, with an eye toward practical applications in future healthcare.

Engineered Assemblies from Constitutionally Isomeric Peptides Modulate Antimicrobial Activity

Antimicrobial peptides (AMPs) are a class of peptides consisting of cationic amino acid residues and a hydrophobic segment, which have been used as an alternative to antibiotics in treating multidrug-resistant bacteria. However, the relationship among the molecular design, assembled structures, and resultant efficacy remains elusive. Herein, we report a class of constitutionally isomeric AMPs assembled into filaments with similar dimensions. Spectroscopic characterizations demonstrated that subtle changes in the position of amino acids led to dramatic variations in molecular packing and surface charges, which were verified by molecular dynamics simulations. In vitro antibacterial assays showed that all AMPs exerted antibacterial activity against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), but the efficacy was dependent on the molecular design. Given the good biocompatibility to eukaryotic cells, these AMPs could be potentially used as antibacterial agents. We believe that this finding provides an avenue to tune the bioactivity of AMPs by rational molecular design.

Development of Membrane-Targeting Osthole Derivatives Containing Pyridinium Quaternary Ammonium Moieties with Potent Anti-Methicillin-Resistant Staphylococcus aureus Properties

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of hospital- and community-acquired infections, necessitating the development of novel antibacterials. Here, we designed and synthesized 30 osthole derivatives with pyridinium quaternary ammonium moieties. In vitro bioassay showed that compounds 8u and 8ac exhibited potent antibacterial activity against S. aureus ATCC 29213 and ten clinical MRSA isolates (MIC = 0.5-1 μg/mL), with low hemolytic activity, rapid bactericidal effects, and minimal resistance induction. In MRSA-infected mouse models of skin abscesses and sepsis, 8u and 8ac also displayed excellent antibacterial effects and safety, which were comparable to vancomycin. Mechanistic studies revealed that 8u and 8ac selectively target bacterial membranes via binding to phosphatidylglycerol (PG), increasing intracellular reactive oxygen species (ROS), inducing content leakage, and ultimately causing bacterial death. These findings suggest 8u and 8ac as promising novel lead candidates for anti-MRSA drug development.

Ultra-short lipopeptides containing d-amino acid exhibiting excellent stability and antibacterial activity against gram-positive bacteria

As novel antibacterial agents, antimicrobial peptides (AMPs) possess broad-spectrum antibacterial activity and low drug resistance, holding significant development potential. Nevertheless, the stability of AMPs significantly restricts their application. In light of this, we synthesized a series of ultra-short lipopeptides using d-amino acid substitution to enhance the stability of ultra-short lipopeptide C12-RRW-NH2 that was selected from our previous research while maintaining its antibacterial activity against gram-positive bacteria. Amongst, the ultra-short lipopeptide Lip7 (C12-rrw-NH2) with full d-amino acid demonstrated outstanding stability in protease, serum, and salt ion environments. It exerted excellent antibacterial activity against gram-positive bacteria, especially against methicillin-resistant Staphylococcus aureus (MRSA). Meanwhile, Lip7 presented a low propensity to develop bacterial resistance with potential for combination therapy with conventional antibiotics. Studies on its antibacterial mechanism revealed that Lip7 could rapidly depolarize the bacterial cytoplasmic membrane, disrupt the integrity of the bacterial membrane, lead to leakage of nucleic acid and protein, promote the generation of reactive oxygen species, and ultimately result in bacterial death. Additionally, Lip7 also exhibited therapeutic potential in both local and systemic MRSA-infected mice models with better safety in vivo. These findings highlighted that Lip7 is an ideal novel antibacterial alternative to offer guiding schemes for developing high-stability antimicrobial peptides to fight multidrug-resistant gram-bacteria.

Single or double lipid-modified ultra-short antimicrobial peptides for treating infections caused by resistant bacteria

Unmodified ultra-short antimicrobial peptides (AMPs) have difficulty attaining high antimicrobial activity and low toxicity concurrently. Our previous studies have shown that single-site lipid modification can enhance the antimicrobial activity of AMPs. However, research on multi-site modification is scarce. This study designed and synthesized a series of single/double-site lipid-modified ultra-short AMPs. Particularly, the new single-site lipid-modified AMP C12 (C12-KKWW-NH2) and double-site lipid-modified AMP DC8 [(C8)2-KKKWW-NH2] showed high bacterial membrane selectivity and presented high stability. It is worth noting that C12 and DC8 exert excellent antibacterial effects on clinically resistant bacteria and have an extremely low resistance tendency. When combined with conventional antibiotics, they show synergistic antibacterial activity against resistant bacteria and curb the resistance of the antibiotics. Additionally, the novel ultra-short AMPs reveal non-receptor-mediated membrane bactericidal mechanisms and can kill the tested bacteria rapidly. Moreover, both C12 and DC8 have high antibacterial activity and low toxicity in vivo. These results suggest that both single-site and multi-site lipid modifications can produce highly efficient AMPs.

Ergosterol depletion by fish AMP analogs likely enhances fungal membrane permeability

The molecular interactions between a fungal membrane model and SJGAP, a 32-amino-acid antimicrobial peptide (AMP) derived from skipjack tuna GAPDH, as well as four analogs, were investigated using molecular dynamics simulations and Fourier transform infrared (FTIR) spectroscopy. In a previous study, Analog 7, modified by replacing three alanine residues with leucine residues, exhibited unique antifungal activity without any antibacterial effect. This contrasts with other analogs, which showed both antifungal and antibacterial effects. In this study, Analog 7 displayed the strongest interactions with the membrane's hydrophobic core, inserting more deeply and causing significantly greater membrane deformation and thinning compared with the other analogs. Its presence caused significant membrane deformation, evident from the displacement of both the phosphate groups and terminal methyls of the lipids. Notably, Analog 7 was the only analog to induce a marked depletion of ergosterol around the peptide insertion site. FTIR spectroscopy experiments further confirmed the distinctive impact of Analog 7 on a fungal membrane model. The combined results from molecular dynamics simulations and spectroscopy emphasize the critical role of leucine substitutions in Analog 7, particularly at residues 18 and 19 within the central α helix, in promoting membrane thinning and inducing ergosterol depletion, suggesting increased membrane permeabilization, which could explain its previously reported antifungal specificity. This study provides the first insights into the molecular interactions between a GAPDH-derived AMP and a fungal membrane model, offering valuable information about its antifungal mechanism of action.

An Analysis of Intrinsic Protein Disorder in Antimicrobial Peptides

Antibiotic resistance, driven by the rise of pathogens like VRE and MRSA, poses a global health threat, prompting the exploration of antimicrobial peptides (AMPs) as alternatives to traditional antibiotics. AMPs, known for their broad-spectrum activity and structural flexibility, share characteristics with intrinsically disordered proteins, which lack a rigid structure and play diverse roles in cellular processes. This study aims to quantify the intrinsic disorder and liquid-liquid phase separation (LLPS) propensity in AMPs, advancing our understanding of their antimicrobial mechanisms and potential therapeutic applications. To investigate the propensity for intrinsic disorder and LLPS in AMPs, we compared the AMPs to the human proteome. The AMP sequences were retrieved from the AMP database (APD3), while the human proteome was obtained from the UniProt database. We analyzed amino acid composition using the Composition Profiler tool and assessed intrinsic disorder using various predictors, including PONDR® and IUPred, through the Rapid Intrinsic Disorder Analysis Online (RIDAO) platform. For LLPS propensity, we employed FuzDrop, and FuzPred was used to predict context-dependent binding behaviors. Statistical analyses, such as ANOVA and χ2 tests, were performed to determine the significance of observed differences between the two groups. We analyzed over 3000 AMPs and 20,000 human proteins to investigate differences in amino acid composition, intrinsic disorder, and LLPS potential. Composition analysis revealed distinct differences in amino acid abundance, with AMPs showing an enrichment in both order-promoting and disorder-promoting amino acids compared to the human proteome. Intrinsic disorder analysis, performed using a range of predictors, consistently demonstrated that AMPs exhibit higher levels of predicted disorder than human proteins, with significant differences confirmed by statistical tests. LLPS analysis, conducted using FuzDrop, showed that AMPs had a lower overall propensity for LLPS compared to human proteins, although specific subsets of AMPs exhibited high LLPS potential. Additionally, redox-dependent disorder predictions highlighted significant differences in how AMP and human proteins respond to oxidative conditions, further suggesting functional divergences between the two proteomes. CH-CDF plot analysis revealed that AMPs and human proteins occupy distinct structural categories, with AMPs showing a greater proportion of highly disordered proteins compared to the human proteome. These findings underscore key molecular differences between AMPs and human proteins, with implications for their antimicrobial activity and potential therapeutic applications. Our study reveals that AMPs possess a significantly higher degree of intrinsic disorder and specific subsets exhibit LLPS potential, distinguishing them from the human proteome. These molecular characteristics likely contribute to their antimicrobial function and adaptability, offering valuable insights for developing novel therapeutic strategies to combat antibiotic resistance.

Enhanced antibacterial and antibiofilm activities of quaternized ultra-highly deacetylated chitosan against multidrug-resistant bacteria

Multidrug-resistant (MDR) bacterial infections pose a severe threat to global public health and present significant challenges in the treatment of bacterial keratitis. The escalation of antimicrobial resistance (AMR) underscores the urgent need for alternative therapeutic strategies. In this study, we report the homogeneous synthesis of quaternized ultra-highly deacetylated chitosan (QUDCS) using a sequential acid-base combination approach. The optimized QUDCS-2 exhibits broad-spectrum antibacterial activity through a membrane-disruption mechanism driven by electrostatic, hydrogen bonding, and hydrophobic interactions, while maintaining low cytotoxicity and high selectivity. Compared to less deacetylated counterparts, QUDCS-2 demonstrates superior stability in enzyme-rich environments and effectively inhibits and eradicates mature biofilms of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. Furthermore, QUDCS-2 exhibits a remarkable ability to prevent the development of antimicrobial resistance. In a mouse keratitis model, QUDCS-2 shows excellent biocompatibility and significant antibacterial efficacy, providing strong support for its potential as a long-term, effective antimicrobial agent.

Neuraminidase and pH responsive nano-drug against resistant Glaesserella parasuis

Glaesserella parasuis (GPS) infection leads to significant economic losses in livestock, with antibiotic resistance exacerbating the issue. The lengthy development cycle of new drugs further complicates timely intervention. Neuraminidase, a virulence factor of GPS, plays a critical role in infection progression. This study presents PSA-Gly-TD, a dual-responsive nanomicelle drug delivery system designed to target neuraminidase and pH variations, offering a solution to the problem of drug-resistant GPS infections. By covalently linking polysialic acid with Tildipirosin, nanoparticles with excellent dispersibility, stability, and a drug encapsulation efficiency of 99.27 % were synthesized. The system demonstrated a particle size of 64.75 nm, accelerated drug release in pathological conditions, and significantly enhanced cellular uptake-nearly three times higher than Tildipirosin alone while maintaining cell viability above 90 %. PSA-Gly-TD preserved the antibacterial efficacy of Tildipirosin and exhibited superior bactericidal activity against drug-resistant GPS strains. In animal models, PSA-Gly-TD showed a stable metabolic profile, reduced tissue damage, and avoided hemolysis, making it a safe and effective option for treating drug-resistant bacterial infections. These results underscore PSA-Gly-TD as a promising therapeutic agent, offering an innovative approach to combating antimicrobial resistance in veterinary medicine and addressing critical challenges in livestock health.

Advances in Antimicrobial Peptides: Mechanisms, Design Innovations, and Biomedical Potential

This comprehensive review explores the advancements in the study of antimicrobial peptides (AMPs), highlighting their potential as promising alternatives to conventional antibiotics in the context of growing antibiotic resistance. AMPs are small molecular proteins found ubiquitously in nature, exhibiting broad-spectrum antimicrobial activity, including antibacterial, antiviral, and antifungal effects, and are vital components of the innate immune system. Due to their non-specific membrane-disrupting mechanism, AMPs are emerging as effective candidates for novel anti-infective agents. The integration of AMPs with biomaterials, such as nanoparticles, liposomes, polymers, and hydrogels, enhances their stability and efficacy while offering multifunctional therapeutic benefits. These combinations promote diverse antibacterial mechanisms, including membrane disruption, intracellular metabolic interference, cell wall modulation, and immune system activation. Despite challenges, such as toxicity, stability, and resistance, innovative strategies including computer-aided design and structural modification show promise in optimizing AMPs' activity, targeting precision, and biocompatibility. The potential for AMPs in clinical applications remains highly promising, with significant opportunities for overcoming antimicrobial resistance through novel AMP-based therapeutic strategies.

Frog-derived synthetic peptides display anti-infective activity against Gram-negative pathogens

Novel antibiotics are urgently needed since bacteria are becoming increasingly resistant to existing antimicrobial drugs. Furthermore, available antibiotics are broad spectrum, often causing off-target effects on host cells and the beneficial microbiome. To overcome these limitations, we used structure-guided design to generate synthetic peptides derived from Andersonin-D1, an antimicrobial peptide (AMP) produced by the odorous frog Odorrana andersonii. We found that both hydrophobicity and net charge were critical for its bioactivity, enabling the design of novel, optimized synthetic peptides. These peptides selectively targeted Gram-negative pathogens in single cultures and complex microbial consortia, showed no off-target effects on human cells or beneficial gut microbes, and did not select for bacterial resistance. Notably, they also exhibited in vivo activity in two preclinical murine models. Overall, we present synthetic peptides that selectively target pathogenic infections and offer promising preclinical antibiotic candidates.

The importance role of central proline to the antimicrobial potency and selectivity of indolicidin

The increasing prevalence of multidrug-resistant pathogens urged the development of new therapeutic strategies, and antimicrobial peptides (AMPs) have emerged as promising candidates. Indolicidin, a proline-rich AMP, is effective against a wide range of pathogens by penetrating the membrane to disrupt the cytoplasmic membrane or inhibit DNA synthesis. This study investigates the impact of replacing the central proline residue in Indolicidin with glycine (IND-7G), D-proline (IND-7DP), or lysine (IND-7K). Results show that both glycine and D-proline substitutions significantly reduced antimicrobial activity with lower hemolysis than the parent peptide. Besides, the analog having lysine substitution (IND-7K) slightly increased activity against E. coli and C. albicans but reduced potency against S. aureus, E. faecalis, and K. pneumoniae. The hemolytic activity of IND-7K remained comparable to that of Indolicidin. These findings demonstrated the essential role of proline in maintaining the antimicrobial efficacy of Indolicidin.

Triazination/IEDDA Cascade Modular Strategy Installing Pyridines/Pyrimidines onto Tyrosine Enables Peptide Screening and Optimization

Modular chemical postmodification of peptides is a promising strategy that supports the optimization and innovation of hit peptide therapeutics by enabling rapid derivatization. However, current methods are primarily limited to traditional bio-orthogonal strategies and chemical ligation techniques, which require the preintroduction of non-natural amino acids and impose fixed methods that limit peptide diversity. Here, we developed the Tyrosine-1,2,3-Triazine Ligation (YTL) strategy, which constructs novel linkages (pyridine and pyrimidine) through a "one-pot, two-step" process combining SNAr and IEDDA reactions, promoting modular post modification of Tyr-containing peptides. After optimizing the YTL strategy and establishing standard procedures, we successfully applied it to the solid-phase postmodification of various biorelated peptides, such as the synthesis of dual-mode imaging probes and long-acting GLP-1 analogs. As a proof of concept, a library of 384 amphipathic peptides was constructed using YTL based on 96-well microfiltration plates. Modular modifications were then performed on the screened template tripeptide RYR, leading to the generation of 20 derivatives. The antibacterial activity of these derivatives was systematically characterized, identifying Z8 as a potential antibacterial candidate.

Beyond antibiotics: exploring multifaceted approaches to combat bacterial resistance in the modern era: a comprehensive review

Antibiotics represent one of the most significant medical breakthroughs of the twentieth century, playing a critical role in combating bacterial infections. However, the rapid emergence of antibiotic resistance has become a major global health crisis, significantly complicating treatment protocols. This paper provides a narrative review of the current state of antibiotic resistance, synthesizing findings from primary research and comprehensive review articles to examine the various mechanisms bacteria employ to counteract antibiotics. One of the primary sources of antibiotic resistance is the improper use of antibiotics in the livestock industry. The emergence of drug-resistant microorganisms from human activities and industrial livestock production has presented significant environmental and public health concerns. Today, resistant nosocomial infections occur following long-term hospitalization of patients, causing the death of many people, so there is an urgent need for alternative treatments. In response to this crisis, non-antibiotic therapeutic strategies have been proposed, including bacteriophages, probiotics, postbiotics, synbiotics, fecal microbiota transplantation (FMT), nanoparticles (NPs), antimicrobial peptides (AMPs), antibodies, traditional medicines, and the toxin-antitoxin (TA) system. While these approaches offer innovative solutions for addressing bacterial infections and preserving the efficacy of antimicrobial therapies, challenges such as safety, cost-effectiveness, regulatory hurdles, and large-scale implementation remain. This review examines the potential and limitations of these strategies, offering a balanced perspective on their role in managing bacterial infections and mitigating the broader impact of antibiotic resistance.

Evolutionary trajectory of bacterial resistance to antibiotics and antimicrobial peptides in Escherichia coli

The global crisis of antimicrobial resistance poses a major threat to human health, underscoring the urgency of developing new antibacterial strategies. Antimicrobial peptides (AMPs) are promising alternatives to antibiotic therapy, yet potential microbial resistance is of great concern. Resistance is often accompanied by fitness costs, which may in turn influence the spread of drug-resistant bacteria and their susceptibility to other antimicrobial agents. Herein, we investigate the evolutionary trajectory of bacterial resistance to antibiotics and AMPs in Escherichia coli, and evaluate the fitness costs and collateral sensitivity of drug-resistant strains. We reveal that E. coli develops resistance to antibiotics, particularly ciprofloxacin and kanamycin, at a notably faster rate than to AMPs. Moreover, antibiotic-evolved strains exhibit slightly higher fitness costs than AMP-evolved bacteria, primarily manifested in reduced bacterial growth and swimming motility. Notably, we demonstrate that trimethoprim-resistant E. coli, with mutations in thyA gene, displays enhanced susceptibility to pexiganan, as evidenced by both in vitro and in vivo studies. Overall, our findings shed new insights for the clinical deployment of AMPs and propose innovative therapeutic strategies for combating antibiotic-resistant bacterial infections.IMPORTANCEThe global spread of antimicrobial resistance necessitates the development of innovative anti-infective strategies. Antimicrobial peptides (AMPs) represent promising alternatives in the post-antibiotic era. By monitoring the evolutionary trajectory of bacterial resistance to eight antibiotics and ten AMPs in Escherichia coli, we demonstrate that E. coli exhibits slower emergence of resistance against AMPs compared with antibiotics. Additionally, these antibiotic-resistant strains incur significant fitness costs, particularly in bacterial growth and motility. Most importantly, we find that some antibiotic-resistant strains show collateral sensitivity to specific AMPs in both in vitro and animal infection models, which is conducive to accelerating the development of AMP-based antibacterial treatment.

Facially amphiphilic skeleton-derived antibacterial crown ether/silver ion complexes

Silver and its derivatives have been widely explored for their antibacterial properties in the treatment of bacterial infections. However, the biological toxicity of silver limits its further development and application. In this study, we designed a facially amphiphilic skeleton incorporating crown ether moieties based on the dendrimer D-CA6-CE. The high-density crown ether units within this structure enable the chelation of silver ions, forming facially amphiphilic skeleton-derived D-CA6-CE/Ag+ complexes. These results indicate that D-CA6-CE/Ag+ can self-assemble into nano-micelles in aqueous solution. D-CA6-CE/Ag+ exhibited high antibacterial activity against Escherichia coli and Staphylococcus aureus, significantly reducing the minimum inhibitory concentrations (MICs) of Ag+ to 6.13 ± 0.19 and 7.33 ± 0.13 μg mL-1, respectively. This antibacterial efficacy surpassed that of silver sulfadiazine, primarily attributed to the enhanced ability to disturb and destroy bacterial membranes by introducing the amphiphilic structure of the cholic acid units. In addition, D-CA6-CE/Ag+ also exhibited lower hemolysis (approximately four times lower) and reduced cytotoxicity compared to silver sulfadiazine. This was likely due to the micellar structure formed by D-CA6-CE/Ag+, which further decreases the direct contact between Ag+ and cells. In summary, the D-CA6-CE/Ag+ complex, with its facially amphiphilic skeletons, exhibited superior antibacterial performance and lower biological toxicity than silver sulfadiazine does. These properties highlight its potential as a promising candidate for the treatment of bacterial infections.

Strong Membrane Permeabilization Activity Can Reduce Selectivity of Cyclic Antimicrobial Peptides

Selectivity is a key requirement for membrane-active antimicrobials to be viable in therapeutic contexts. Therefore, the rational design or suitable selection of new compounds requires adequate mechanistic understanding of peptide selectivity. In this study, we compare two similar cyclic peptides that differ only in the arrangement of their three hydrophobic tryptophan (W) and three positively charged arginine (R) residues, yet exhibit different selectivities. This family of peptides has previously been shown to target the cytoplasmic membrane of bacteria, but not to act directly by membrane permeabilization. We have systematically studied and compared the interactions of the two peptides with zwitterionic phosphatidylcholine (PC) and negatively charged phosphatidylglycerol/phosphatidylethanolamine (PG/PE) model membranes using various biophysical methods to elucidate the mechanism of the selectivity. Like many antimicrobial peptides, the cyclic, cationic hexapeptides investigated here bind more efficiently to negatively charged membranes than to zwitterionic ones. Consequently, the two peptides induce vesicle leakage, changes in lipid packing, vesicle aggregation, and vesicle fusion predominantly in binary, negatively charged PG/PE membranes. The peptide with the larger hydrophobic molecular surface (three adjacent W residues) causes all these investigated effects more efficiently. In particular, it induces leakage by asymmetry stress and/or leaky fusion in zwitterionic and charged membranes, which may contribute to high activity but reduces selectivity. The unselective type of leakage appears to be driven by the more pronounced insertion into the lipid layer, facilitated by the larger hydrophobic surface of the peptide. Therefore, avoiding local accumulation of hydrophobic residues might improve the selectivity of future membrane-active compounds.

Identification of antimicrobial peptides from the Ambystoma mexicanum displaying antibacterial and antitumor activity

Antibiotic resistance is a significant healthcare concern. Therefore, identifying target molecules that can serve as antibiotic substitutes is crucial. Among the promising candidates are antimicrobial peptides (AMPs). AMPs are defense mechanisms of the innate immune system which exist in almost all living organisms. Research on the AMPs of some amphibians has shown that, in addition to their antimicrobial effectiveness, AMPs also exhibit anti-inflammatory and anti-carcinogenic properties. In this study, we identify and characterize AMPs deriving from the skin mucus of the axolotl (Ambystoma mexicanum). Upon activity spectrum evaluation of the AMPs, we synthesized and ranked 22 AMPs according to antimicrobial efficacy by means of a prediction tool. To assess the AMPs' potential as antibacterial and anticarcinogenic compounds, we performed a minimum inhibitory concentration (MIC) assay for efficacy against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA), and an apoptosis assay on T-47D mammary carcinoma cells. We identified four AMPs that showed significant inhibition of MRSA, of which three also demonstrated anticarcinogenic activity. Gene expression analysis was performed on AMP-stimulated carcinoma cells using a breast cancer-specific RT-PCR array. In cells stimulated with the AMPs, gene expression analysis showed upregulation of tumor suppressor genes and downregulation of oncogenes. Overall, our work demonstrates the antimicrobial and anticarcinogenic activity of axolotl-derived AMPs. The results of this work serve as a basis to further investigate the mode of action and potential use of axolotl AMPs as therapeutic anticancer or antibiotic agents.

Microneedle technology for enhanced topical treatment of skin infections

Skin infections caused by microbes such as bacteria, fungi, and viruses often lead to aberrant skin functions and appearance, eventually evolving into a significant risk to human health. Among different drug administration paradigms for skin infections, microneedles (MNs) have demonstrated superiority mainly because of their merits in enhancing drug delivery efficiency and reducing microbial resistance. Also, integrating biosensing functionality to MNs offers point-of-care wearable medical devices for analyzing specific pathogens, disease status, and drug pharmacokinetics, thus providing personalized therapy for skin infections. Herein, we do a timely update on the development of MN technology in skin infection management, with a special focus on how to devise MNs for personalized antimicrobial therapy. Notably, the advantages of state-of-the-art MNs for treating skin infections are pointed out, which include hijacking sequential drug transport barriers to enhance drug delivery efficiency and delivering various therapeutics (e.g., antibiotics, antimicrobial peptides, photosensitizers, metals, sonosensitizers, nanoenzyme, living bacteria, poly ionic liquid, and nanomoter). In addition, the nanoenzyme-based multimodal antimicrobial therapy is highlighted in addressing intractable infectious wounds. Furthermore, the MN-based biosensors used to identify pathogen types, track disease status, and quantify antibiotic concentrations are summarized. The limitations of antimicrobial MNs toward clinical translation are offered regarding large-scale production, quality control, and policy guidance. Finally, the future development of biosensing MNs with easy-to-use and intelligent properties and MN-based wearable drug delivery for home-based therapy are prospected. We hope this review will provide valuable guidance for future development in MN-mediated topical treatment of skin infections.

Oxygenous and biofilm-targeted nanosonosensitizer anchored with Pt nanozyme and antimicrobial peptide in the gelatin/sodium alginate hydrogel for infected diabetic wound healing

Sonodynamic therapy is an emerging therapeutic approach for combating bacterial infections. However, the characteristics of hypoxia, high H2O2 microenvironment, and the formation of persistent biofilms in diabetic wound sites limit its efficacy in this field. To address these issues, we developed a multifunctional antibacterial hydrogel dressing PPCN@Pt-AMPs/HGel with the cross-linked gelatin and sodium alginate as the matrix, where the nanosonosensitizer PCN-224 was decorated with the oxygen-generating Pt nanoenzyme and further coupled with a biofilm-targeting antimicrobial peptide via an interacting polydopamine layer. This nano-composite hydrogel displayed improved mechanical properties as well as good biocompatibility and biodegradability. The catalase-like activity of the nanoparticles facilitated the ultrasound-induced generation of the singlet oxygen due to the catalytic decomposition of the H2O2 into O2. In vitro results showed that the hydrogel dressing exhibited excellent antimicrobial ability under low-intensity ultrasound stimulation, which could effectively inhibit the newly formed biofilm and eliminate the full-grown biofilms. In the infected diabetic wound of rats, PPCN@Pt-AMPs/HGel significantly enhanced the wound healing rate under low-intensity ultrasound stimulation and improved the regeneration outcomes by promoting granulation tissue formation, angiogenesis, and type III collagen deposition. In conclusion, our study provides a novel and effective antibacterial hydrogel dressing for sonodynamic treatment of diabetic wounds.

Association of idealized amphiphiles and protease inhibitors: Conferring antimicrobial peptides with stable antibacterial activity under physiological conditions to combat multidrug-resistant bacteria

AIMS

The unstable antimicrobial activity of antimicrobial peptides (AMPs) under physiological conditions (especially the degradation instigated proteases) seems to be a persistent impediment for their successful implementation in clinical trials. Consequently, our objective was to devise AMP engineering frameworks that could sustain robust antibacterial efficacy within physiological environments.

METHODS

In this work, we harvested AMPs with stable antimicrobial activity under the physiological barriers through the combination of idealized amphiphiles and trypsin inhibitors.

RESULTS

We screened and identified the lead peptides IK3-A and IK3-S, which showed potent activity against Gram-negative bacteria, including multidrug-resistant (MDR) bacteria, and exhibited promising biocompatibility with mammalian cells. Remarkably, IK3-A and IK3-S maintained sustained antibacterial potency under physiological salts, serum, and protease conditions. Furthermore, both IK3-A and IK3-S kill Gram-negative bacteria by attacking the bacterial cell membrane and inducing oxidative damage (at high concentrations). Crucially, IK3-A and IK3-S have optimal safety and efficacy in mice.

CONCLUSIONS

This is the first work to compare the effects of different trypsin inhibitors on the resistance of AMPs to protease hydrolysis on the same sequence platform. In conclusion, these findings provide guidance for the molecular design of AMPs with stable antibacterial activity under physiological conditions and facilitates the process of clinical translation of AMPs as antimicrobial biomaterials against MDR bacteria. Moreover, this may stimulate a more general interest in protease inhibitors as molecular scaffolds in the creation of highly stable peptide-based biomaterials.

Phage-Encoded Antimicrobial Peptide gp28 Demonstrates LL-37-Like Antimicrobial Activity Against Multidrug-Resistant Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa (P. aeruginosa) is a gram-negative bacterial pathogen commonly associated with nosocomial infections. Treatment of P. aeruginosa infections is notoriously difficult due to biofilm formation and antibiotic resistance. Antimicrobial peptides (AMPs) are thought to be promising new antimicrobials. Gp28, a phage-derived AMP, is a novel class of characterized phage AMPs with activity against Escherichia coli in a manner similar to the human peptide LL-37. LL-37 exhibits strong antimicrobial activity against P. aeruginosa as well as biofilm disruption and synergy with certain antibiotics posing the question whether gp28 could act similarly.

Methods

Antibacterial activity of gp28 against P. aeruginosa was established using growth inhibition assays, with minimum inhibitory concentration calculated. Biofilm disruption was assessed using crystal violet staining and scanning electron microscopy. Combined treatment of gp28 with tobramycin against P. aeruginosa was measured using a modified time-kill assay at sublethal concentrations.

Results

Gp28 inhibits P. aeruginosa planktonic growth, with a minimum inhibitory concentration of 109 μg mL-1 and disrupts established biofilms. We demonstrate that gp28 increases the susceptibility of P. aeruginosa to tobramycin.

Conclusions

Gp28 demonstrates potential for development as a putative therapeutic agent against a clinically resistant P. aeruginosa strain either alone or in combination with the frontline antibiotic tobramycin.