Development and Challenges of Antimicrobial Peptides for Therapeutic Applications

Serum-Stable, Cationic, α-Helical AMPs to Combat Infections of ESKAPE Pathogens and C. albicans

Expedition in the rate of development of antimicrobial resistance accompanied by the slowdown in the development of new antimicrobials has led to a dire necessity to develop an alternate class of antimicrobial agents. Antimicrobial peptides (AMPs), available in nature, are effective molecules that can combat microbial infections. However, due to several inherent shortcomings such as salt sensitivity of their potency, short systemic half-lives owing to protease and serum degradation, and cytotoxicity, their commercial success is limited. Inspired by α helical AMPs present in nature, here in this work, we have developed two short, cationic, helical AMPs RR-12 and FL-13. Both peptides exhibited high broad-spectrum antimicrobial activity, salt tolerance, prompt bactericidal activity, considerable serum stability, remaining non-cytotoxic and non-hemolytic at relevant microbicidal concentrations. The designed AMPs were membranolytic toward the microbial strains, though there were subtle differences in the mechanism owing to the variation in the composition of the cell membranes in different microbes. Rigorous experimental techniques and molecular dynamics (MD) simulations were performed to understand the structure, activity, and their mechanisms in detail. Positive charge, balanced hydrophobicity-hydrophilicity, and helical conformation were the different attributes that led to the development of the superior performance of the AMPs, making them valuable additions to the repertoire of therapeutically promising antimicrobials.

Antimicrobial peptides: from discovery to developmental applications

Antimicrobial resistance (AMR) has emerged as a significant crisis in global health. Due to their advantageous properties, antimicrobial peptides (AMPs) have garnered considerable attention as a potential alternative therapy to address the AMR crisis. These peptides might disrupt cell membranes or cell walls to exhibit antimicrobial activity, or modulate the immune response to promote recovery from diseases. In recent years, significant progress has been made in the research of AMPs, alongside the emergence of new challenges. This review first systematically summarizes and critically discusses recent advancements in understanding the characteristics and current landscapes of AMPs, as well as their regulatory mechanisms of action and practical applications, particularly those reported or approved within the last 5 years. Additionally, the principles, paths for their identification, and future research trends in AMPs are also analyzed following a discussion of the advantages and disadvantages of AMPs in comparison to conventional antibiotics. Unlike significant prior literature in this field, this report has summarized the latest major discovery methods for AMPs and, more importantly, emphasized their practical applications by supporting various viewpoints using selected examples of AMPs' applications in real-life scenarios. Besides, some emerging hot topics of AMPs, including those derived from gut microbiota and their potential synergistic effects in combating AMR, were profiled. All of these indicate the originality of the report and provide valuable references for future AMP discoveries and applications.

Staphylococcus hominis as a source of antimicrobial peptides: identification of a new peptide with potential antimicrobial properties using in silico approach

The rapid progression of antimicrobial resistance, fueled by the excessive use of antibiotics, has become a major public health concern. Among the pathogens contributing to this crisis, Staphylococcus aureus stands out as a significant therapeutic challenge, especially with the rise of resistant strains like Methicillin-Resistant S. aureus (MRSA). In this context, antimicrobial peptides (AMPs) emerge as a promising alternative, thanks to their unique mechanisms of action. Exploring the genomes of species such as Staphylococcus hominis, known for producing AMPs effective against S. aureus, offers promising opportunities for discovering novel therapeutic agents. In this study, Average Nucleotide Identity (ANI) combined with phylogenetic analysis identified a potential emerging subspecies of Staphylococcus hominis. The core genome analysis led to the identification of a potential antimicrobial peptide. The peptide model simulated with the S. aureus membrane model in molecular dynamics revealed that it interacts primarily with the lipids head groups, leading to an overall rigidification of the bacterial membrane.

In Vivo Acute Toxicity and Therapeutic Potential of a Synthetic Peptide, DP1 in a Staphylococcus aureus Infected Murine Wound Excision Model

Bacterial infections at the surgical sites are one of the most prevalent skin infections that impair the healing mechanism. They account for about 20% of all types of infections and lead to approximately 75% of surgical-site infection-associated mortality. Several antibiotics, such as cephalosporins, fluoroquinolones, quinolones, penicillin, sulfonamides, etc., that are used to treat such wound infections not only counter infections but also disrupt the normal flora. Moreover, antibiotics, when used for a prolonged duration, may impair the formation of new blood vessels, delay collagen production, or inhibit the migration of certain cells involved in wound repair, leading to an impaired healing process. Therefore, there is a dire need for alternate therapeutic approaches against such infections. Antimicrobial peptides have gained considerable attention as a promising strategy to counter these pathogens and prevent the spread of infection. Recently, we have reported a designed peptide, DP1, and its broad-spectrum in vitro antimicrobial activity against Gram-positive and Gram-negative bacteria. In the present study, in vivo acute toxicity of DP1 was evaluated and even at a high dose (20 mg/kg body weight) of DP1, a 100% survival of mice was observed. Subsequently, a Staphylococcus aureus-infected murine wound excision model was established to assess the wound healing efficacy of DP1. The study revealed significant wound healing vis-a-vis attenuated S. aureus bioburden at the wound site and also controlled the oxidative stress depicting anti-oxidant activity as well. Healing of the infected wounds was also verified by histopathological examination. Based on the results of this study, it can be concluded that DP1 improves wound resolution despite infections and promotes the healing mechanism. Hence, DP1 holds compelling potential as a novel antimicrobial drug that requires further explorations in clinical platforms.

Simulation studies to identify high-affinity probiotic peptides for inhibiting PAK1 gastric cancer protein: A comparative approach

A major threat to world health is the high death rate from gastrointestinal (GI) cancer, especially in Asia, South America, and Europe. The new approaches are needed because of the complexity and heterogeneity of gastrointestinal (GI) cancer, which has made the development of effective treatments difficult. To investigate the potential of peptide-based therapies that target the P21 Activated Kinase 1 (PAK1) in GI cancer, we are using the DBsORF database to predict peptides from the genomes of two bacterial strains: Lactobacillus plantarum and Pediococcus pentosaceus. Energy minimization is then applied for stability after the three-dimensional (3D) structures of these peptides are modeled using the Swiss Model tool. ToxinPred is used for toxicity analysis to verify the safety profiles of the identified peptides. The three-dimensional structure of the target protein PAK1 is taken out of the Protein Data Bank (PDB) and ready for computer analyses. To identify the top-performing peptides for each strain that have good PAK1 binding properties, molecular docking analysis is performed using the ClusPro server. The peptide repertoires of L.plantarum and P. pentosaceus are distinct, and some candidates display low toxicity; for instance, VOIOYA_1513 from P. pentosaceus and BVNTGZ_2921 from L. plantarum demonstrate high binding energies and stable interactions with PAK1. Once the binding energies, hydrogen bonds, and non-bonded contacts have been evaluated, promising peptide candidates are selected. Understanding the dynamics of the peptide-PAK1 complexes is achieved through molecular dynamics simulations performed with the Groningen machine for molecular simulation (Gromacs). Trajectory analysis measures like Radius of Gyration (Rg), Root Mean Square Deviation (RMSD), and Root Mean Square Fluctuation (RMSF) provide insight into the stability and fluctuations of the structure during a 100 ns simulation. Molecular dynamics simulations validate the stability of these complexes, suggesting that, subject to further experimental validation, they could be promising therapeutic candidates. Future research projects and drug development initiatives will benefit from the detailed computational approach, which offers information about the design and evaluation of peptide-based treatments that target PAK1 in GI cancer.

Antimicrobial Peptides and Their Mimetics: Promising Candidates of Next-Generation Therapeutic Agents Combating Multidrug-Resistant Bacteria

The increasing morbidity and mortality caused by multidrug-resistant bacteria alerts human beings to the fact that conventional antibiotics are no longer reliable and effective alternatives are imperatively needed. Owing to wide range of sources, diverse structures, and unique mode of action, antimicrobial peptides have been highly anticipated and extensively studied in recent years. Besides, the integration of artificial intelligence helps researchers gain access to the vast unexplored chemical space, which opens more opportunities for the optimization and design of novel structures. Moreover, Due to advances in chemistry and synthetic biology, researchers have also begun to focus on the potential of chemical mimetics of antimicrobial peptides. In this review, a comprehensive discussion about natural and synthesized antimicrobial peptides as well as their chemical mimetics is made, so as to provide a comprehensive summary of this field and inspire follow-up research.

Generation of VacA-targeting guide peptides to increase specific antimicrobial peptide toxicity against Helicobacter pylori

BACKGROUND

The H. pylori virulence factors VacA and CagA are the primary determinants of gastric cancer globally. In this study we increased the activity of antimicrobial peptides (AMPs) against H. pylori by using phage display against VacA to rapidly generate peptides targeting VacA, subsequently fusing these peptides to the AMP N-terminus to confer specificity.

RESULTS

After four rounds of phage display, 36 phage clones were ranked for whole cell H. pylori binding by ELISA. The displayed 12-mer peptides of the top nine candidate clones were fused to GFP as guide peptides and analyzed for binding to wild type H. pylori 60190 and a ∆vacA strain. The three guides with the best differential binding were fused to the AMP pexiganan using two different linker peptides. All guide/linker combinations led to increased toxicity against H. pylori and most also decreased off-target toxicity. Guide P5 linked to pexiganan was the top configuration, delivering 64- to > 256-fold differential toxicity against H. pylori compared to off-target bacteria and a therapeutic window exceeding 128-fold when tested against cultured gastric cells.

CONCLUSIONS

Guide peptide biopanning provides an effective, scalable method to increase specific activity of antimicrobial peptides based on attraction to a key virulence factor.

Advances in antimicrobial peptides: From mechanistic insights to chemical modifications

This review provides a comprehensive analysis of antimicrobial peptides (AMPs), exploring their diverse sources, secondary structures, and unique characteristics. The review explores into the mechanisms underlying the antibacterial, immunomodulatory effects, antiviral, antiparasitic and antitumour of AMPs. Furthermore, it discusses the three principal synthesis pathways for AMPs and assesses their current clinical applications and preclinical research status. The paper also addresses the limitations of AMPs, including issues related to stability, resistance, and toxicity, while offering insights into strategies for their enhancement. Recent advancements in AMP research, such as chemical modifications (including amino acid sequence optimisation, terminal and side-chain modifications, PEGylation, conjugation with small molecules, conjugation with photosensitisers, metal ligands, polymerisation, cyclisation and specifically targeted antimicrobial peptides) are highlighted. The goal is to provide a foundation for the future design and optimisation of AMPs.

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.

Advance in peptide-based drug development: delivery platforms, therapeutics and vaccines

The successful approval of peptide-based drugs can be attributed to a collaborative effort across multiple disciplines. The integration of novel drug design and synthesis techniques, display library technology, delivery systems, bioengineering advancements, and artificial intelligence have significantly expedited the development of groundbreaking peptide-based drugs, effectively addressing the obstacles associated with their character, such as the rapid clearance and degradation, necessitating subcutaneous injection leading to increasing patient discomfort, and ultimately advancing translational research efforts. Peptides are presently employed in the management and diagnosis of a diverse array of medical conditions, such as diabetes mellitus, weight loss, oncology, and rare diseases, and are additionally garnering interest in facilitating targeted drug delivery platforms and the advancement of peptide-based vaccines. This paper provides an overview of the present market and clinical trial progress of peptide-based therapeutics, delivery platforms, and vaccines. It examines the key areas of research in peptide-based drug development through a literature analysis and emphasizes the structural modification principles of peptide-based drugs, as well as the recent advancements in screening, design, and delivery technologies. The accelerated advancement in the development of novel peptide-based therapeutics, including peptide-drug complexes, new peptide-based vaccines, and innovative peptide-based diagnostic reagents, has the potential to promote the era of precise customization of disease therapeutic schedule.

Advancing Nanotechnology: Targeting Biofilm-Forming Bacteria with Antimicrobial Peptides

Nanotechnology offers innovative solutions for addressing the challenges posed by biofilm-forming bacteria, which are highly resistant to conventional antimicrobial therapies. This review explores the integration of pharmaceutical nanotechnology with antimicrobial peptides (AMPs) to enhance the treatment of biofilm-related infections. The use of various nanoparticle systems-including inorganic/metallic, polymeric, lipid-based, and dendrimer nanostructures-provides promising avenues for improving drug delivery, targeting, and biofilm disruption. These nanocarriers facilitate the penetration of biofilms, down-regulate biofilm-associated genes, such as ALS1, ALS3, EFG1, and HWP1, and inhibit bacterial defense mechanisms through membrane disruption, reactive oxygen species generation, and intracellular targeting. Furthermore, nanoparticle formulations such as NZ2114-NPs demonstrate enhanced efficacy by reducing biofilm bacterial counts by several orders of magnitude. This review highlights the potential of combining nanotechnology with AMPs to create novel, targeted therapeutic approaches for combatting biofilm-related infections and overcoming the limitations of traditional antimicrobial treatments.

Harnessing bacterial antimicrobial peptides: a comprehensive review on properties, mechanisms, applications, and challenges in combating antimicrobial resistance

Antimicrobial resistance (AMR) is a significant global health concern due to the persistence of pathogens and the emergence of resistance in bacterial infections. Bacterial-derived antimicrobial peptides (BAMPs) have emerged as a promising strategy to combat these challenges. Known for their diversity and multifaceted nature, BAMPs are notable bioactive agents that exhibit potent antimicrobial activities against various pathogens. This review explores the intricate properties and underlying mechanisms of BAMPs, emphasizing their diverse applications in addressing AMR. Additionally, the review investigates the mechanisms, analyses the challenges in utilizing BAMPs effectively, and examines their potential applications and associated deployment challenges providing comprehensive insights into how BAMPs can be harnessed to combat AMR across different domains. The significance of this review lies in highlighting the potential of BAMPs as transformative agents in combating AMR, offering sustainable and eco-friendly solutions to this pressing global health challenge.

Future applications of cyclic antimicrobial peptides in drug delivery

INTRODUCTION

Cyclic antimicrobial peptides (CAMPs) are gaining attention as promising candidates in advanced drug delivery systems due to their structural stability, resistance to proteolytic degradation, and versatile therapeutic potential. Their unique properties enable applications that extend beyond combating multidrug-resistant (MDR) pathogens. Their amphipathic and cell-penetrating properties allow them to efficiently transport drugs across cellular membranes.

AREAS COVERED

This review explores the structural advantages and mechanisms of action of CAMPs, emphasizing their role in drug delivery. The literature analysis (2010-2024) from PubMed, Scopus, and Web of Science highlights developments in CAMP-conjugated therapies, liposomal formulations, and encapsulation systems. The review also examines their antimicrobial potency, amphipathic and cell-penetrating properties, and integration into nanocarrier technologies to enhance drug stability, bioavailability, and precision targeting. Challenges such as toxicity, scalability, and cost are also discussed. CAMPs have the potential to revolutionize drug delivery through their robustness and multifunctionality, particularly in precision medicine.

EXPERT OPINION

Future advancements in peptide engineering, nanotechnology, and AI-driven design are expected to enhance CAMPs' therapeutic specificity, reduce toxicity, and broaden their applications, including oncology and gene therapy, paving the way for their integration into next-generation therapeutics.

Preclinical Evaluation of the Safety, Toxicity and Efficacy of Genetically Modified Wharton's Jelly Mesenchymal Stem/Stromal Cells Expressing the Antimicrobial Peptide SE-33

Mesenchymal stem/stromal cells (MSCs) offer promising therapeutic potential in cell-based therapies for various diseases. However, the safety of genetically modified MSCs remains poorly understood. This study aimed to evaluate the general toxicity and safety of Wharton's Jelly-Derived MSCs (WJ-MSCs) engineered to express the antimicrobial peptide SE-33 in an animal model. Genetically modified WJ-MSCs expressing SE-33 were administered to C57BL/6 mice at both therapeutic and excessive doses, either once or repeatedly. Animal monitoring included mortality, clinical signs, and behavioral observations. The toxicity assessment involved histopathological, hematological, and biochemical analyses of major organs and tissues, while immunotoxicity and immunogenicity were examined through humoral and cellular immune responses, macrophage phagocytic activity, and lymphocyte blast transformation. Antimicrobial efficacy was evaluated in a Staphylococcus aureus-induced pneumonia model by monitoring animal mortality and assessing bacterial load and inflammatory processes in the lungs. Mice receiving genetically modified WJ-MSCs exhibited no acute or chronic toxicity, behavioral abnormalities, or pathological changes, regardless of the dose or administration frequency. No significant immunotoxicity or alterations in immune responses were observed, and there were no notable changes in hematological or biochemical serum parameters. Infected animals treated with WJ-MSC-SE33 showed a significant reduction in bacterial load and lung inflammation and improved survival compared to control groups, demonstrating efficacy over native WJ-MSCs. Our findings suggest that WJ-MSCs expressing SE-33 are well tolerated, displaying a favorable safety profile comparable to native WJ-MSCs and potent antimicrobial activity, significantly reducing bacterial load, inflammation, and mortality in an S. aureus pneumonia model. These data support the safety profile of WJ-MSCs expressing SE-33 as a promising candidate for cell-based therapies for bacterial infections, particularly those complicated by antibiotic resistance.

Carboxy-Amidated AamAP1-Lys has Superior Conformational Flexibility and Accelerated Killing of Gram-Negative Bacteria

C-terminal amidation of antimicrobial peptides (AMPs) is a frequent minor modification used to improve antibacterial potency, commonly ascribed to increased positive charge, protection from proteases, and a stabilized secondary structure. Although the activity of AMPs is primarily associated with the ability to penetrate bacterial membranes, hitherto the effect of amidation on this interaction has not been understood in detail. Here, we show that amidation of the scorpion-derived membranolytic peptide AamAP1-Lys produces a potent analog with faster bactericidal activity, increased membrane permeabilization, and greater Gram-negative membrane penetration associated with greater conformational flexibility. AamAP1-lys-NH2 has improved antibiofilm activity against Acinetobacter baumannii and Escherichia coli, benefits from a two- to 3-fold selectivity improvement, and provides protection against A. baumannii infection in a Galleria mellonella burn wound model. Circular dichroism spectroscopy shows both peptides adopt α-helix conformations in the steady state. However, molecular dynamics (MD) simulations reveal that, during initial binding, AamAP1-Lys-NH2 has greater conformation heterogeneity, with substantial polyproline-II conformation detected alongside α-helix, and penetrates the bilayer more readily than AamAP1-Lys. AamAP1-Lys-NH2 induced membrane permeabilization of A. baumannii occurs only above a critical concentration with slow and weak permeabilization and slow killing occurring at its lower MIC but causes greater and faster permeabilization than AamAP1-Lys, and kills more rapidly, when applied at equal concentrations. Therefore, while the increased potency of AamAP1-Lys-NH2 is associated with slow bactericidal killing, amidation, and the conformational flexibility it induces, affords an improvement in the AMP pharmacodynamic profile and may need to be considered to achieve improved therapeutic performance.

Unfolding the Potential of Pyrrole- and Indole-Based Allylidene Hydrazine Carboximidamides as Antimicrobial Agents

Antimicrobial drug resistance is a significant global health challenge, causing hundreds of thousands of deaths annually and severely impacting healthcare systems worldwide. Several reported antimicrobial compounds have a guanidine motif, as the positive charge on guanidine promotes cell lysis. Therefore, pyrrole- and indole-based allylidene hydrazine carboximidamide derivatives with guanidine motifs are proposed as antimicrobial agents that mimic cationic antimicrobial peptides (CAMPs). A total of 72 derivatives having pyrrol-2-yl-phenyl allylidene hydrazine carboximidamide and indol-3-yl-phenyl allylidene hydrazine carboximidamide scaffolds were assessed for their inhibitory potential against a panel of Gram-positive and Gram-negative bacteria. Analogs 1j, 1k, 1s, 2j, 2q, 4a, 4c, 4h, 5b, 6a, and 6d exhibited potent broad-spectrum antimicrobial activity better than the standard antibiotics. Also, these compounds showed no cytotoxicity up to 3-fold of the minimum inhibitory concentration, and structure-activity relationship was established. Further, the most active compound, 6a, showed a strong biofilm disruption, acted on the bacterial membrane, and lysed it. The further development of these compounds as novel antimicrobial agents is warranted.

FDA-Approved Antibacterials and Echinocandins

Since 1955, a total of 12 peptide-based drugs with antimicrobial or antifungal properties have received approval from the Food and Drug Administration (FDA). Peptides present a promising opportunity to address serious infections that may be challenging to manage through other means. Peptides exhibit the capability to leverage various mechanisms, and in some cases, multiple mechanisms are employed for this purpose. Despite the initial approval dating back to 1955, the FDA recently approved an echinocandin peptide just last year. The ongoing approvals underscore the significance of peptides in addressing ongoing medical challenges. Approximately 22 peptide therapeutics with an antibacterial and antifungal spectrum are currently undergoing various phases of clinical trials, showing promising results. In this review, antimicrobial and antifungal peptides are analyzed in terms of their chemical structure, indication, mode of action, and development journey, concluding with their arrival in the pharmaceutical market.

Protease-Resistant, Broad-Spectrum Antimicrobial Peptides with High Antibacterial and Antifungal Activity

Antimicrobial peptides (AMPs) are a diverse group of small, naturally occurring molecules that orchestrate the innate immune response of various organisms, from microorganisms to humans. Characterized by their broad-spectrum activity against bacteria, fungi and viruses, AMPs are increasingly recognized for their potential as novel therapeutic agents in the face of rising antibiotic resistance. Here, we present several newly designed AMPs, one of which, DTN6, exerts significant activity against several organisms with MIC values as low as 0.5 µg/mL. The D-TN6 peptide influences both bacteria and yeasts. Scanning electron microscopy and transmission electron microscopy results showed that the bacterial membrane is affected by D-TN6, which is resistant to proteases and is effective against antibiotic-resistant pathogens with hemolytic activity and low toxicity. The D-TN6 peptide is effective in vivo against standard S. aureus strains in wounds. Thus, D-TN6 is a potent antibiotic candidate with a broad spectrum of activity. Overall, AMPs are a promising tool for the development of next-generation antimicrobial agents that could mitigate global health threats posed by multidrug-resistant pathogens.

Cliotide U1, a Novel Antimicrobial Peptide Isolated From Urtica Dioica Leaves

Aims

Antibiotic resistance is currently a major challenge to scientists. Thus, attempts have been made to develop new compounds with antimicrobial activity. In this research, a new antimicrobial peptide with antibacterial activity was isolated from the plant Urtica dioica.

Methods

A new antimicrobial peptide, named cliotide U1, was purified through precipitation with ammonium sulfate and reverse-phase high-performance liquid chromatography. In silico methods analyzed the physicochemical properties of cliotide U1. The properties of the peptide, including antibacterial activity, pH stability, heat stability, cytotoxicity, and hemolytic activity, were also examined.

Findings

The purified peptide was composed of 35 amino acids with a hydrophobicity ratio of 63% and a net charge of + 5. The antibacterial activity of cliotide U1 was observed against gram-negative and gram-positive bacteria with a minimum inhibitory concentration (MIC) of 1 to 4 µM. Cliotide U1 had less than 2% cytotoxic activity at the MIC range against the human embryonic kidney cell line 293 with no clear hemolytic activity. The stability of cliotide U1 was preserved at various temperatures (10-60°C) and pH (6-9).

Conclusion

Our results demonstrated that cliotide U1 had potent antibacterial potential against gram-negative and gram-positive bacteria. Considering its properties, cliotide U1 can be introduced as a novel antibacterial candidate for expanding new therapeutic drugs.

Decoding the Role of Antimicrobial Peptides in the Fight against Mycobacterium tuberculosis

Tuberculosis (TB), a leading infectious disease caused by the pathogen Mycobacterium tuberculosis, poses a significant treatment challenge due to its unique characteristics and resistance to existing drugs. The conventional treatment regimens, which are lengthy and involve multiple drugs, often result in poor patient adherence and subsequent drug resistance, particularly with multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains. This highlights the urgent need for novel anti-TB therapies and new drug targets. Antimicrobial peptides (AMPs), which are natural host defense molecules present in all living organisms, offer a promising alternative to traditional small-molecule drugs. AMPs have several advantages, including their broad-spectrum activity and the potential to circumvent existing resistance mechanisms. However, their clinical application faces challenges such as stability, delivery, and potential toxicity. This review aims to provide essential information on AMPs, including their sources, classification, mode of action, induction within the host under stress, efficacy against M. tuberculosis, clinical status and hurdles to their use. It also highlights future research directions to address these challenges and advance the development of AMP-based therapies for TB.

Identifying Opportunity Targets in Gram-Negative Pathogens for Infectious Disease Mitigation

Antimicrobial drug resistance (AMR) is a pressing global human health challenge. Humans face one of their grandest challenges as climate change expands the habitat of vectors that bear human pathogens, incidences of nosocomial infections rise, and new antibiotics discovery lags. AMR is a multifaceted problem that requires a multidisciplinary and an "all-hands-on-deck" approach. As chemical microbiologists, we are well positioned to understand the complexities of AMR while seeing opportunities for tackling the challenge. In this Outlook, we focus on vulnerabilities of human pathogens and posit that they represent "opportunity targets" for which few modulatory ligands exist. We center our attention on proteins in Gram-negative organisms, which are recalcitrant to many antibiotics because of their external membrane barrier. Our hope is to highlight such targets and explore their potential as "druggable" proteins for infectious disease mitigation. We posit that success in this endeavor will introduce new classes of antibiotics that might alleviate some of the current pressing AMR concerns.

Effect of Chirality and Amphiphilicity on the Antimicrobial Activity of Tripodal Lysine-Based Peptides

A series of tripodal (three-arm) lysine-based peptides were designed and synthesized and their self-assembly properties in aqueous solution and antimicrobial activity were investigated. We compare the behaviors of homochiral tripodal peptides (KKY)3K and a homologue containing the bulky aromatic fluorenylmethoxycarbonyl (Fmoc) group Fmoc-(KKY)3K, and heterochiral analogues containing k (d-Lys), (kkY)3K and Fmoc-(kkY)3K. The molecular conformation and self-assembly in aqueous solutions were probed using various spectroscopic techniques, along with small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM). In cell viability assays using fibroblast cell lines, the tripodal peptides without Fmoc were observed to be noncytotoxic over the concentration range studied, and the Fmoc functionalized tripodal peptides were only cytotoxic at the highest concentrations (above the critical aggregation concentration of the lipopeptides). The molecules also show good hemocompatibility at sufficiently low concentration, and antimicrobial activity was assessed via MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) assays. These revealed that the Fmoc-functionalized tripodal peptides had significant activity against both Gram-negative and Gram-positive bacteria, and in the case of Gram-positive Staphylococcus aureus, the antimicrobial activity for Fmoc-(kkY)3K was improved compared to polymyxin B. The mechanism of the antimicrobial assay was found to involve rupture of the bacterial membrane as evident from fluorescence microscopy live/dead cell assays, and scanning electron microscopy images.

Molecular Dynamics Simulations of Structurally Nanoengineered Antimicrobial Peptide Polymers Interacting with Bacterial Cell Membranes

Multidrug resistance (MDR) to conventional antibiotics is one of the most urgent global health threats, necessitating the development of effective and biocompatible antimicrobial agents that are less inclined to provoke resistance. Structurally nanoengineered antimicrobial peptide polymers (SNAPPs) are a novel and promising class of such alternatives. These star-shaped polymers are made of a dendritic core with multiple arms made of copeptides with varying amino acid sequences. Through a comprehensive set of in vivo experiments, we previously showed that SNAPPs with arms made of random blocks of lysine (K) and valine (V) residues exhibit sub-μM efficacy against Gram-negative and Gram-positive bacteria tested. Cryo-TEM images suggested pore formation by a SNAPP with random block copeptide arms as one of their modes of actions. However, the molecular mechanisms responsible for this mode of action of SNAPPs are not fully understood. To address this gap, we employed an atomistic molecular dynamics simulation technique to investigate the influence of three different sequences of amino acids, namely (1) alt-block KKV, (2) ran-block, and (3) diblock motifs on the secondary structure of their arms and SNAPP's overall configuration as well as their interactions with lipid bilayer. We, for the first time, identified a step-by-step mechanism through which alt-block and random SNAPPs interact with lipid bilayer and lead to "pore formation", hence, cell death. These insights provide a strong foundation for further optimization of the chemical structure of SNAPPs for maximum performance against MDR bacteria, therefore offering a promising avenue for addressing antibiotic resistance and the development of effective antibacterial agents.

Novel active Trp- and Arg-rich antimicrobial peptides with high solubility and low red blood cell toxicity designed using machine learning tools

BACKGROUND

Given the rising number of multidrug-resistant (MDR) bacteria, there is a need to design synthetic antimicrobial peptides (AMPs) that are highly active, non-hemolytic, and highly soluble. Machine learning tools allow the straightforward in silico identification of non-hemolytic antimicrobial peptides.

METHODS

Here, we utilized a number of these tools to rank the best peptides from two libraries comprised of: 1) a total of 8192 peptides with sequence bhxxbhbGAL, where b is the basic amino acid R or K, h is a hydrophobic amino acid, i.e. G, A, L, F, I, V, Y, or W and x is Q, S, A, or V; and 2) a total of 512 peptides with sequence RWhxbhRGWL, where b and h are as for the first library and x is Q, S, A, or G. The top 100 sequences from each library, as well as 10 peptides predicted to be active but hemolytic (for a total of 220 peptides), were SPOT synthesized and their IC50 values were determined against S. aureus USA 300 (MRSA).

RESULTS

Of these, 6 AMPs with low IC50's were characterized further in terms of: MICs against MRSA, E. faecalis, K. pneumoniae, E.coli and P. aeruginosa; RBC lysis; secondary structure in mammalian and bacterial model membranes; and activity against cancer cell lines HepG2, CHO, and PC-3.

CONCLUSION

Overall, the approach yielded a large family of active antimicrobial peptides with high solubility and low red blood cell toxicity. It also provides a framework for future designs and improved machine learning tools.

AI Methods for Antimicrobial Peptides: Progress and Challenges

Antimicrobial peptides (AMPs) are promising candidates to combat multidrug-resistant pathogens. However, the high cost of extensive wet-lab screening has made AI methods for identifying and designing AMPs increasingly important, with machine learning (ML) techniques playing a crucial role. AI approaches have recently revolutionised this field by accelerating the discovery of new peptides with anti-infective activity, particularly in preclinical mouse models. Initially, classical ML approaches dominated the field, but recently there has been a shift towards deep learning (DL) models. Despite significant contributions, existing reviews have not thoroughly explored the potential of large language models (LLMs), graph neural networks (GNNs) and structure-guided AMP discovery and design. This review aims to fill that gap by providing a comprehensive overview of the latest advancements, challenges and opportunities in using AI methods, with a particular emphasis on LLMs, GNNs and structure-guided design. We discuss the limitations of current approaches and highlight the most relevant topics to address in the coming years for AMP discovery and design.

Plant Antimicrobial Peptides and Their Main Families and Roles: A Review of the Literature

Antimicrobial peptides (AMPs) are constituent molecules of the innate defense system and are naturally produced by all organisms. AMPs are characterized by a relatively low molecular weight (less than 10 kDa) and a variable number of cysteine residues that form disulfide bonds and contribute to the stabilization of the tertiary structure. In addition, there is a wide repertoire of antimicrobial agents against bacteria, viruses, fungi, and protozoa that can provide a large number of prototype peptides for study and biochemical manipulation. In this sense, plant AMPs stand out because they have a wide range of biological functions against microorganisms and potential applications in medicine and agriculture. Herein, we describe a mini-review of the principal AMP families, such as defensins, lipid transfer proteins (LTPs), thionins, heveins, and cyclotides. The objective of this work was to present the main discoveries regarding the biological activities of these plant AMP families, especially in the last 20 years. We also discuss the current knowledge of their biological activities, gene expression, and possible uses as antimicrobial molecules and in plant biotechnology.

Accelerating antimicrobial peptide design: Leveraging deep learning for rapid discovery

Antimicrobial peptides (AMPs) are excellent at fighting many different infections. This demonstrates how important it is to make new AMPs that are even better at eliminating infections. The fundamental transformation in a variety of scientific disciplines, which led to the emergence of machine learning techniques, has presented significant opportunities for the development of antimicrobial peptides. Machine learning and deep learning are used to predict antimicrobial peptide efficacy in the study. The main purpose is to overcome traditional experimental method constraints. Gram-negative bacterium Escherichia coli is the model organism in this study. The investigation assesses 1,360 peptide sequences that exhibit anti- E. coli activity. These peptides' minimal inhibitory concentrations have been observed to be correlated with a set of 34 physicochemical characteristics. Two distinct methodologies are implemented. The initial method involves utilizing the pre-computed physicochemical attributes of peptides as the fundamental input data for a machine-learning classification approach. In the second method, these fundamental peptide features are converted into signal images, which are then transmitted to a deep learning neural network. The first and second methods have accuracy of 74% and 92.9%, respectively. The proposed methods were developed to target a single microorganism (gram negative E.coli), however, they offered a framework that could potentially be adapted for other types of antimicrobial, antiviral, and anticancer peptides with further validation. Furthermore, they have the potential to result in significant time and cost reductions, as well as the development of innovative AMP-based treatments. This research contributes to the advancement of deep learning-based AMP drug discovery methodologies by generating potent peptides for drug development and application. This discovery has significant implications for the processing of biological data and the computation of pharmacology.

Natural Antimicrobial Peptides and Their Synthetic Analogues for Effective Oral Microflora Control and Oral Infection Treatment-The Role of Ceragenins in the Development of New Therapeutic Methods

Oral diseases, both acute and chronic, of infectious or non-infectious etiology, represent some of the most serious medical problems in dentistry. Data from the literature increasingly indicate that changes in the oral microbiome, and therefore, the overgrowing of pathological microflora, lead to a variety of oral-localized medical conditions such as caries, gingivitis, and periodontitis. In recent years, compelling research has been devoted to the use of natural antimicrobial peptides as therapeutic agents in the possible treatment of oral diseases. This review focuses on the potential of ceragenins (CSAs), which are lipid analogs of natural antimicrobial peptides, as molecules for the development of new methods for the prevention and treatment of oral diseases. Studies to date indicate that ceragenins, with their spectrum of multidirectional biological activities, including antimicrobial, tissue regeneration-stimulating, anti-inflammatory, and immunomodulatory properties, are strong candidates for further development of oral formulations. However, many of the beneficial properties of ceragenins require confirmation in experimental conditions reproducing the oral environment to fully determine their application potential. Their transition to practical use also requires more advanced testing of these molecules in clinical trials, which have only been conducted in limited numbers to date.

SAMP: Identifying antimicrobial peptides by an ensemble learning model based on proportionalized split amino acid composition

It is projected that 10 million deaths could be attributed to drug-resistant bacteria infections in 2050. To address this concern, identifying new-generation antibiotics is an effective way. Antimicrobial peptides (AMPs), a class of innate immune effectors, have received significant attention for their capacity to eliminate drug-resistant pathogens, including viruses, bacteria, and fungi. Recent years have witnessed widespread applications of computational methods especially machine learning (ML) and deep learning (DL) for discovering AMPs. However, existing methods only use features including compositional, physiochemical, and structural properties of peptides, which cannot fully capture sequence information from AMPs. Here, we present SAMP, an ensemble random projection (RP) based computational model that leverages a new type of feature called proportionalized split amino acid composition (PSAAC) in addition to conventional sequence-based features for AMP prediction. With this new feature set, SAMP captures the residue patterns like sorting signals at both the N-terminal and the C-terminal, while also retaining the sequence order information from the middle peptide fragments. Benchmarking tests on different balanced and imbalanced datasets demonstrate that SAMP consistently outperforms existing state-of-the-art methods, such as iAMPpred and AMPScanner V2, in terms of accuracy, Matthews correlation coefficient (MCC), G-measure, and F1-score. In addition, by leveraging an ensemble RP architecture, SAMP is scalable to processing large-scale AMP identification with further performance improvement, compared to those models without RP. To facilitate the use of SAMP, we have developed a Python package that is freely available at https://github.com/wan-mlab/SAMP.

Host defense peptides at the crossroad of endothelial cell physiology: Insight into mechanistic and pharmacological implications

Antimicrobial peptides (AMPs), particularly host defense peptides (HDPs), have gained recognition for their role in host defense mechanisms, but they have also shown potential as a promising anticancer, antiviral, antiparasitic, antifungal and immunomodulatory agent. Research studies in recent years have shown HDPs play a crucial role in endothelial cell function and biology. The function of endothelial cells is impacted by HDPs' complex interplay between cytoprotective and cytotoxic actions as they are known to modulate barrier integrity, inflammatory response and angiogenesis. This biphasic response varies and depends on the peptide structure, its concentration, and the microenvironment. These effects are mediated through key signaling pathways, including MAPK, NF-κB, and PI3K/Akt, which controls responses such as cell proliferation, apoptosis, and migration. In the present review, we have discussed the significance of the intriguing relationship between HDPs and endothelial cell physiology which suggests it potential as a therapeutic agents for the treating wounds, cardiovascular diseases, and inflammation-related endothelial damage.

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

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

Klebsiella pneumoniae capsular polysaccharide: Mechanism in regulation of synthesis, virulence, and pathogenicity

Hypervirulent Klebsiella pneumoniae exhibits strong pathogenicity and can cause severe invasive infections but is historically recognized as antibiotic-susceptible. In recent years, the escalating global prevalence of antibiotic-resistant hypervirulent K. pneumoniae has raised substantial concerns and created an urgent demand for effective treatment options. Capsular polysaccharide (CPS) is one of the main virulence determinants contributing to the hypervirulent phenotype. The structure of CPS varies widely among strains, and both the structure and composition of CPS can influence the virulence of K. pneumoniae. CPS possesses various immune evasion mechanisms that promote the survival of K. pneumoniae, as well as its colonization and dissemination. Given the proven viability of therapies that target the capsule, improving our understanding of the CPS structure is critical to effectively directing treatment strategies. In this review, the structure and typing of CPS are addressed as well as genes related to synthesis and regulation, relationships with virulence, and pathogenic mechanisms. We aim to provide a reference for research on the pathogenesis of K. pneumoniae.

The proline-rich antimicrobial peptide B7-005: low bacterial resistance, safe for human cells and effective in zebrafish embryo bacteraemia model

Proline-rich antimicrobial peptides (PrAMPs) have gained attention due to their antimicrobial properties and low cytotoxicity. B7-005, a small optimized PrAMP, exhibits a broader spectrum of activity than native PrAMPs, due to an antimicrobial mechanism based on inhibiting prokaryotic protein synthesis and destabilizing bacterial membranes. However, the toxicity and the in vivo efficacy of B7-005 remain poorly understood, so in vitro and in vivo microbiology and toxicology experiments were used to assess its suitability as an anti-infective agent. The incidence of resistance towards B7-005 by E. coli was lower than for other PrAMPs and antibiotics; moreover, it maintained antimicrobial activity in the presence of human serum. B7-005 exerted its antimicrobial effect at a much lower concentration than those causing harmful effects on four different cell types, such as membrane permeabilization or non-lytic depolarization of mitochondria. The latter effect may be related to the inhibition of eukaryotic protein synthesis by B7-005 observed in vitro. In a zebrafish embryo model, B7-005 was well tolerated and reduced mortality from pre-existing E. coli bacteraemia. Overall, B7-005 was safe for human cells and effective against systemic infection in vivo, making it a promising lead for developing new antibiotics.

Antiviral and antibacterial peptides: Mechanisms of action

Antimicrobial peptides (AMPs) present promising alternatives for addressing bacterial and viral multidrug resistance due to their distinctive properties. Understanding the mechanisms of these compounds is essential for achieving this objective. Therefore, this comprehensive review aims to highlight primary natural sources of AMPs and elucidate various aspects of the modes of action of antiviral and antibacterial peptides (ABPs). It emphasizes that antiviral peptides (AVPs) can disrupt the replication cycle of both enveloped and non-enveloped viruses at several stages, including pre-fusion, fusion, and post-entry into the host cell. Additionally, the review discusses the inhibitory effects of ABPs on bacterial growth, outlining their extracellular actions as well as their intracellular activities following membrane translocation. Factors such as structure, size, electric charge, environmental factors, degrading enzymes, and microbial resistance against AMPs can affect the function of AMPs.

Development of cell-free platforms for discovering, characterizing, and engineering post-translational modifications

Post-translational modifications (PTMs) are important for the stability and function of many therapeutic proteins and peptides. Current methods for studying and engineering PTM installing proteins often suffer from low-throughput experimental techniques. Here we describe a generalizable, in vitro workflow coupling cell-free protein synthesis (CFPS) with AlphaLISA for the rapid expression and testing of PTM installing proteins. We apply our workflow to two representative classes of peptide and protein therapeutics: ribosomally synthesized and post-translationally modified peptides (RiPPs) and conjugate vaccines. First, we demonstrate how our workflow can be used to characterize the binding activity of RiPP recognition elements, an important first step in RiPP biosynthesis, and be integrated into a biodiscovery pipeline for computationally predicted RiPP products. Then, we adapt our workflow to study and engineer oligosaccharyltransferases (OSTs) involved in conjugate vaccine production, enabling the identification of mutant OSTs and sites within a carrier protein that enable high efficiency production of conjugate vaccines. In total, we expect that our workflow will accelerate design-build-test cycles for engineering PTMs.

Antimicrobial Peptides: The Game-Changer in the Epic Battle Against Multidrug-Resistant Bacteria

The rapid progress of antibiotic resistance among bacteria has prompted serious medical concerns regarding how to manage multidrug-resistant (MDR) bacterial infections. One emerging strategy to combat antibiotic resistance is the use of antimicrobial peptides (AMPs), which are amino acid chains that act as broad-spectrum antimicrobial molecules and are essential parts of the innate immune system in mammals, fungi, and plants. AMPs have unique antibacterial mechanisms that offer benefits over conventional antibiotics in combating drug-resistant bacterial infections. Currently, scientists have conducted multiple studies on AMPs for combating drug-resistant bacterial infections and found that AMPs are a promising alternative to conventional antibiotics. On the other hand, bacteria can develop several tactics to resist and bypass the effect of AMPs. Therefore, it is like a battle between the bacterial community and the AMPs, but who will win? This review provides thorough insights into the development of antibiotic resistance as well as detailed information about AMPs in terms of their history and classification. Furthermore, it addresses the unique antibacterial mechanisms of action of AMPs, how bacteria resist these mechanisms, and how to ensure AMPs win this battle. Finally, it provides updated information about FDA-approved AMPs and those that were still in clinical trials. This review provides vital information for researchers for the development and therapeutic application of novel AMPs for drug-resistant bacterial infections.

Influence of Nisin Grafting on the Antibacterial Efficacy of AMP Self-Assembled Monolayers (SAMs)

The use of antimicrobial peptides (AMPs) covalently grafted on surfaces has been recognized in recent years as a promising strategy to fight against biofilm formation. However, after grafting, the understanding of AMP-bacteria interactions is still debated in the literature. In this study, Nisin, a cyclic AMP, was grafted onto gold surfaces via an indirect grafting on acidic thiol self-assembled monolayers using succinimide linkers. The physical and chemical properties of these SAMs were then finely characterized by XPS and FT-IR to confirm the covalent grafting of Nisin. The antiadhesion and bactericidal effects were then studied for Escherichia coli ATCC25922, Staphylococcus aureus ATCC 25923, and Listeria ivanovii Li4(pVS2) by a posteriori analysis of the culture supernatants (i.e., indirect technique) and ex situ by optical microscopy following crystal violet staining (i.e., direct technique). Statistical analysis reveals that the Nisin coating has bactericidal and antiadhesive properties towards Gram-positive bacteria, while no significant results were obtained for Gram-negative bacteria.

Role of Peptide Associations in Enhancing the Antimicrobial Activity of Adepantins: Comparative Molecular Dynamics Simulations and Design Assessments

Adepantins are peptides designed to optimize antimicrobial biological activity through the choice of specific amino acid residues, resulting in helical and amphipathic structures. This paper focuses on revealing the atomistic details of the mechanism of action of Adepantins and aligning design concepts with peptide behavior through simulation results. Notably, Adepantin-1a exhibits a broad spectrum of activity against both Gram-positive and Gram-negative bacteria, while Adepantin-1 has a narrow spectrum of activity against Gram-negative bacteria. The simulation results showed that one of the main differences is the extent of aggregation. Both peptides exhibit a strong tendency to cluster due to the amphipathicity embedded during design process. However, the more potent Adepantin-1a forms smaller aggregates than Adepantin-1, confirming the idea that the optimal aggregations, not the strongest aggregations, favor activity. Additionally, we show that incorporation of the cell penetration region affects the mechanisms of action of Adepantin-1a and promotes stronger binding to anionic and neutral membranes.

Antibacterial activity of recombinant liver-expressed antimicrobial peptide-2 derived from olive flounder, Paralichthys olivaceus

Liver-expressed antimicrobial peptide-2 (LEAP-2) is a cysteine-rich peptide that plays a crucial role in the innate immune system of fish. To investigate the molecular function of LEAP-2 from olive flounder, Paralichthys olivaceus, we cloned the gene encoding LEAP-2 using PCR and expressed it in Escherichia coli. Analysis of LEAP-2 expression revealed predominant transcripts in the liver and lower levels in the intestine of olive flounder, whereas their expression levels in the liver and head kidney increased, during the initial stage of infection with the aquapathogenic bacterium Edwardsiella piscicida. Recombinant LEAP-2 (rOfLEAP-2) purified from E. coli exhibited antimicrobial activity, as demonstrated by the ultrasensitive radial diffusion assay, against both Gram-positive (Bacillus subtilis, Streptococcus parauberis, and Lactococcus garvieae) and Gram-negative (Vibrio harveyi and E. coli) bacteria, with minimum inhibitory concentrations ranging from 25 to 100 μg/mL depending on the species tested. The antibacterial activity of rOfLEAP-2 was attributed to its ability to disrupt bacterial membranes, validated by the N-phenylnaphthalen-1-amine uptake assays and scanning electron microscope analysis against E. coli, V. harveyi, B. subtilis, and L. garvieae treated with rOfLEAP-2. Furthermore, a synergistic enhancement of antibacterial activity was observed when rOfLEAP-2 was combined with ampicillin or synthetic LEAP-1 peptide, suggesting a distinct mechanism of action from those of other antimicrobial agents. These findings provide evidence for the antibacterial efficacy of LEAP-2 from olive flounder, highlighting its potential therapeutic application against pathogenic bacteria.

Recent Progress in Terrestrial Biota Derived Antibacterial Agents for Medical Applications

Conventional antibiotic and multidrug treatments are becoming less and less effective and the discovery of new effective and safe antibacterial agents is becoming a global priority. Returning to a natural antibacterial product is a relatively new current trend. Terrestrial biota is a rich source of biologically active substances whose antibacterial potential has not been fully utilized. The aim of this review is to present the current state-of-the-art terrestrial biota-derived antibacterial agents inspired by natural treatments. It summarizes the most important sources and newly identified or modified antibacterial agents and treatments from the last five years. It focuses on the significance of plant- animal- and bacteria-derived biologically active agents as powerful alternatives to antibiotics, as well as the advantages of utilizing natural antibacterial molecules alone or in combination with antibiotics. The main conclusion is that terrestrial biota-derived antibacterial products and substances open a variety of new ways for modern improved therapeutic strategies. New terrestrial sources of known antibacterial agents and new antibacterial agents from terrestrial biota were discovered during the last 5 years, which are under investigation together with some long-ago known but now experiencing their renaissance for the development of new medical treatments. The use of natural antibacterial peptides as well as combinational therapy by commercial antibiotics and natural products is outlined as the most promising method for treating bacterial infections. In vivo testing and clinical trials are necessary to reach clinical application.

Antimicrobial Peptides Derived from Bacteria: Classification, Sources, and Mechanism of Action against Multidrug-Resistant Bacteria

Antimicrobial peptides (AMPs) are short, usually cationic peptides with an amphiphilic structure, which allows them to easily bind and interact with the cellular membranes of viruses, bacteria, fungi, and other pathogens. Bacterial AMPs, or bacteriocins, can be produced from Gram-negative and Gram-positive bacteria via ribosomal synthesis to eliminate competing organisms. Bacterial AMPs are vital in addressing the increasing antibiotic resistance of various pathogens, potentially serving as an alternative to ineffective antibiotics. Bacteriocins have a narrow spectrum of action, making them highly specific antibacterial compounds that target particular bacterial pathogens. This review covers the two main groups of bacteriocins produced by Gram-negative and Gram-positive bacteria, their modes of action, classification, sources of positive effects they can play on the human body, and their limitations and future perspectives as an alternative to antibiotics.

Microbiome-derived antimicrobial peptides show therapeutic activity against the critically important priority pathogen, Acinetobacter baumannii

Acinetobacter baumannii is designated by the World Health Organisation as a critical priority pathogen. Previously we discovered antimicrobial peptides (AMPs), namely Lynronne-1, -2 and -3, with efficacy against bacterial pathogens, such as Staphylococcus aureus and Pseudomonas aeruginosa. Here we assessed Lynronne-1, -2 and -3 structure by circular dichroism and efficacy against clinical strains of A. baumannii. All Lynronne AMPs demonstrated alpha-helical secondary structures and had antimicrobial activity towards all tested strains of A. baumannii (Minimum Inhibitory Concentrations 2-128 μg/ml), whilst also having anti-biofilm activity. Lynronne-2 and -3 demonstrated additive effects with amoxicillin and erythromycin, and synergy with gentamicin. The AMPs demonstrated little toxicity towards mammalian cell lines or Galleria mellonella. Fluorescence-based assay data demonstrated that Lynronne-1 and -3 had higher membrane-destabilising action against A. baumannii in comparison with Lynronne-2, which was corroborated by transcriptomic analysis. For the first time, we demonstrate the therapeutic activity of Lynronne AMPs against A. baumannii.

Antimicrobial Peptide Octoprohibitin-Encapsulated Chitosan Nanoparticles Enhanced Antibacterial Activity against Acinetobacter baumannii

Background: This study focused on evaluating the physiochemical characteristics and antibacterial activity of Octoprohibitin-encapsulated CNPs (Octoprohibitin-CNPs) against Acinetobacter baumannii. Methods: Octoprohibitin was encapsulated into CNPs via ionotropic gelation with carboxymethyl chitosan (CMC) and low molecular weight chitosan (CS). Octoprohibitin-CNPs were dispersed in phosphate-buffered saline and the release kinetic profile was determined. Then Octoprohibitin-CNPs were examined using field-emission transmission electron microscopy and physicochemical characterization was performed. Antibacterial activity of Octoprohibitin-CNPs against A. baumannii was evaluated. Biofilm inhibition and eradication assays were performed using the crystal violet (CV) staining-based method for biofilm quantification. Results: The average diameter, zeta potential, encapsulation efficiency, and loading capacity of Octoprohibitin-CNPs were 244.5 ± 21.97 nm, +48.57 ± 0.38 mV, and 85.7% and 34.2%, respectively. TEM analysis imaging revealed that Octoprohibitin-CNPs are irregularly shaped, with fewer aggregates than CNPs. Octoprohibitin-CNPs exhibited a biphasic release pattern, characterized by an initial rapid phase followed by a sustained release over time, extending up to 93.68 ± 6.48% total release until 96 h. In vitro, Octoprohibitin-CNPs showed lower cytotoxicity compared to Octoprohibitin alone. Time-kill kinetic and bacterial viability reduction assays showed Octoprohibitin-CNPs exhibited slightly higher antibacterial activity against A. baumannii than Octoprohibitin. Conclusions: Octoprohibitin-CNP-treated A. baumannii exhibited higher levels of morphological deviation, increased membrane permeability, and the production of reactive oxygen species, as well as antibiofilm activity with greater biofilm inhibition and eradication than Octoprohibitin. These findings show that Octoprohibitin-CNPs perform better against A. baumannii compared to Octoprohibitin alone.

Antagonistic Mechanism Analysis of Bacillus velezensis JLU-1, a Biocontrol Agent of Rice Pathogen Magnaporthe oryzae

Magnaporthe oryzae, the causal agent of rice blast, is a fungal disease pathogen. Bacillus spp. have emerged as the most promising biological control agent alternative to chemical fungicides. In this study, the bacterial strain JLU-1 with significant antagonistic activity isolated from the rhizosphere soil of rice was identified as Bacillus velezensis through whole-genome sequencing, average nucleotide identity analysis, and 16S rRNA gene sequencing. Twelve gene clusters for secondary metabolite synthesis were identified in JLU-1. Furthermore, 3 secondary metabolites were identified in JLU-1, and the antagonistic effect of secondary metabolites against fungal pathogens was confirmed. Exposure to JLU-1 reduced the virulence of M. oryzae, and JLU-1 has the ability to induce the reactive oxygen species production of rice and improve the salt tolerance of rice. All of these results indicated that JLU-1 and its secondary metabolites have the promising potential to be developed into a biocontrol agent to control fungal diseases.

Controlling bacterial growth and inactivation using thin film-based surface acoustic waves

Formation of bacterial films on structural surfaces often leads to severe contamination of medical devices, hospital equipment, implant materials, etc., and antimicrobial resistance of microorganisms has indeed become a global health issue. Therefore, effective therapies for controlling infectious and pathogenic bacteria are urgently needed. Being a promising active method for this purpose, surface acoustic waves (SAWs) have merits such as nanoscale earthquake-like vibration/agitation/radiation, acoustic streaming induced circulations, and localised acoustic heating effect in liquids. However, only a few studies have explored controlling bacterial growth and inactivation behaviour using SAWs. In this study, we proposed utilising piezoelectric thin film-based SAW devices on a silicon substrate for controlling bacterial growth and inactivation with and without using ZnO micro/nanostructures. Effects of SAW powers on bacterial growth for two types of bacteria, i.e., E. coli and S. aureus, were evaluated. Varied concentrations of ZnO tetrapods were also added into the bacterial culture to study their effects and the combined antimicrobial effects along with SAW agitation. Our results showed that when the SAW power was below a threshold (e.g., about 2.55 W in this study), the bacterial growth was apparently enhanced, whereas the further increase of SAW power to a high power caused inactivation of bacteria. Combination of thin film SAWs with ZnO tetrapods led to significantly decreased growth or inactivation for both E. coli and S. aureus, revealing their effectiveness for antimicrobial treatment. Mechanisms and effects of SAW interactions with bacterial solutions and ZnO tetrapods have been systematically discussed.

From In Vitro Promise to In Vivo Reality: An Instructive Account of Infection Model Evaluation of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are regarded as a promising alternative to traditional antibiotics in the face of ever-increasing resistance. However, many AMPs fail to progress into clinics due to unexpected difficulties found in preclinical in vivo phases. Our research has focused on crotalicidin (Ctn), an AMP from snake venom, and a fragment thereof, Ctn[15-34], with improved in vitro antimicrobial and anticancer activities and remarkable serum stability. As the retroenantio versions of both AMPs maintained favorable profiles, in this work, we evaluate the in vivo efficacy of both the native-sequence AMPs and their retroenantio counterparts in a murine infection model with Acinetobacter baumannii. A significant reduction in bacterial levels is found in the mice treated with Ctn[15-34]. However, contrary to expectations, the retroenantio analogs either exhibit toxicity or lack efficacy when administered to mice. Our findings underscore the critical importance of in vivo infection model evaluation to fully calibrate the therapeutic potential of AMPs.

Combatting Fungal Infections: Advances in Antifungal Polymeric Nanomaterials

Fungal pathogens cause over 6.5 million life-threatening systemic infections annually, with mortality rates ranging from 20 to 95%, even with medical intervention. The World Health Organization has recently emphasized the urgent need for new antifungal drugs. However, the range of effective antifungal agents remains limited and resistance is increasing. This Review explores the current landscape of fungal infections and antifungal drugs, focusing on synthetic polymeric nanomaterials like nanoparticles that enhance the physicochemical properties of existing drugs. Additionally, we examine intrinsically antifungal polymers that mimic naturally occurring peptides. Advances in polymer characterization and synthesis now allow precise design and screening for antifungal activity, biocompatibility, and drug interactions. These antifungal polymers represent a promising new class of drugs for combating fungal infections.

Membrane Activity of Melittin and Magainin-I at Low Peptide-to-Lipid Ratio: Different Types of Pores and Translocation Mechanisms

Antimicrobial peptides (AMPs) are believed to be a prominent alternative to the common antibiotics. However, despite decades of research, there are still no good clinical examples of peptide-based antimicrobial drugs for system application. The main reasons are loss of activity in the human body, cytotoxicity, and low selectivity. To overcome these challenges, a well-established structure-function relationship for AMPs is critical. In the present study, we focused on the well-known examples of melittin and magainin to investigate in detail the initial stages of AMP interaction with lipid membranes at low peptide-to-lipid ratio. By combining the patch-clamp technique with the bioelectrochemical method of intramembrane field compensation, we showed that these peptides interact with the membrane in different ways: melittin inserts deeper into the lipid bilayer than magainin. This difference led to diversity in pore formation. While magainin, after a threshold concentration, formed the well-known toroidal pores, allowing the translocation of the peptide through the membrane, melittin probably induced predominantly pure lipidic pores with a very low rate of peptide translocation. Thus, our results shed light on the early stages of peptide-membrane interactions and suggest new insights into the structure-function relationship of AMPs based on the depth of their membrane insertion.