Mechanisms of antimicrobial peptide action and resistance

Discovery of a potent ornithine-modified gramicidin S analogue against drug-resistant Staphylococcus aureus and Enterococcus faecalis with minimal red blood cell toxicity

The high haemolytic toxicity of Gramicidin S restricts its therapeutic use to topical applications. Given the growing need for new antibiotics and drawing inspiration from the cyclic structure and druggable characteristics of Gramicidin S, we have synthesized 15 ornithine (Orn) modified analogous peptides systematically and investigated their antimicrobial activity and cytotoxicity. Results revealed that mono- ornithine residue replaced with tryptophan (11) and arginine (12) peptides showed improved activity against multidrug resistant bacterial strains of Staphylococcus aureus and Enterococcus faecalis (MIC 4-8 μg/mL) compared with comparators vancomycin (MIC >64 μg/mL), levofloxacin (MIC 32-64 μg/mL) and meropenem (MIC 8-64 μg/mL). Cytotoxicity data demonstrated that peptide 11 (HC50 = 112.1 μg/mL) and 12 (HC50 = 186 μg/mL) exhibited greatly reduced haemolytic activity, as compared with Gramicidin S (HC50 = 35.13 μg/mL). The concentration-dependent time-kill kinetic assay resulted the active peptide 12 represents better bactericidal effect compared with 11 and vancomycin. Scanning electron microscope analysis shows that GS and the modified peptide 12 disrupt the bacterial cell surface, causing damage and leading to bacterial cell death. 2D NOESY data of 12 showed that the arginine residue side-chain guanidinium ion and tryptophan indole form a cation-π interaction. This interaction between arginine and tryptophan stabilizes the β-sheet conformation, selectively targets bacterial membranes, hence exhibiting reduced red blood cell toxicity. The overall study suggests that the peptide 12 may be further developed as an antibiotic for systematic use against infections caused due to S. aureus.

Membrane Modification and Adaptation of Metabolism by Acinetobacter baumannii Prompts Resistance to Antimicrobial Activity of Outer Membrane Perturbing Peptide L8

Multidrug resistant (MDR) Acinetobacter baumannii has emerged as one of the most concerning nosocomial pathogens worldwide. One approach to target MDR A. baumannii is treatment with synergistic combinations of outer membrane-permeabilizing antimicrobial peptides (AMP) and antibiotics that otherwise only act against Gram-positive bacteria. Resistance against AMPs is rarely observed, especially when administered in combination with other drugs. Recently, we described the synergistic antimicrobial activity of AMPs L8 and L8S1 with rifampicin against a clinical isolate of A. baumannii. In the current work we explore the mechanisms of action of these peptides. We demonstrate that L8 and L8S1 perturb the cell envelope of A. baumannii. Moreover, we show that resistance against peptide L8 could be acquired in vitro either by increasing the amount of PE lipid on the surface or by increasing biofilm formation. Interestingly, the resistance to the antimicrobial activity of the peptides did not affect membrane perturbation or synergistic activity of the peptides with rifampicin, suggesting a dual mechanism of action for these peptides.

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.

Temporin-GHa derived peptide shows inhibitory efficacy against Cutibacterium acnes and alleviates inflammatory reactions in acne vulgaris

Acne vulgaris is a widespread chronic inflammatory skin disease that is mainly caused by Cutibacterium acnes infection and subsequent inflammation. Temporin-GHaR4G7R (GHaR4G7R) was derived from Temporin-GHa of frog Hylarana guentheri. Its antibacterial performance against C. acnes and potential mechanism against acne vulgaris in vitro and in vivo were evaluated. In vitro tests demonstrated that GHaR4G7R displayed potent bactericidal effects against C. acnes, with both the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 3.1 μM. It exerted antibacterial effect by disrupting the bacterial membranes, accompanied by low propensity for developing drug resistance. GHaR4G7R significantly inhibited the formation of early biofilms and eliminated established biofilms of C. acnes by decreasing exopolysaccharide synthesis. Meanwhile, GHaR4G7R demonstrated an anti-inflammatory effect on HaCaT cells challenged with heat-inactivated C. acnes by significantly down-regulating the expression of TLR2/NF-κB/MAPK pathway-associated proteins by qRT-PCR, immunofluorescence, and Western blot assays. As expected, GHaR4G7R significantly decreased the bacterial colonization in rat ear model induced by C. acnes, and relieved the auricular swelling and inflammatory cell infiltration through inhibiting the TLR2/NF-κB/MAPK signaling pathway, leading to down-regulation of the inflammatory cytokine expression and alleviation of the skin inflammation in vivo. The research indicates that GHaR4G7R might be a potential alternative for developing novel strategies for treating acne vulgaris.

Antimicrobial and Potent Anti-Biofilm Properties of Rationally Designed α-Helix Antimicrobial Peptides

The antimicrobial resistance (AMR) crisis represents a significant global threat. Unlike traditional antibiotics, antimicrobial peptides offer a promising pathway because of their primary mechanisms. This study aimed to evaluate and rationally design novel AMPs based on tobacco nectar's AMP (Pep 6) to combat antibiotic resistance issues. Substitution and truncation of some amino acids were applied. Four peptides, KF19, KF16, LK16, and LR16, were designed with enhanced net charge hydrophobicity. They were evaluated for their in vitro antibacterial activity. However, only promising AMPs were further evaluated for their hemolytic activity, time-killing kinetics, mode of action, and anti-biofilm properties. The results showed that only KF19 and LR16 have potent activity against Staphylococcus aureus ATCC25923 and resistant isolates with MIC values from 7.81 to 15.62 μg/mL. Hemolysis ratios were 2.38% and 2.24% at 125 μg/mL for KF19 and LR16, respectively. Both peptides were able to kill S. aureus ATCC25923 within 2 h. SEM results showed their ability to target the cell membrane. Both peptides destroyed the S. aureus biofilms significantly at 62.5 and 125 μg/mL (**p < 0.01, ***p < 0.001, ****p < 0.0001). This study supported rational design in developing new antibacterial agents and demonstrated the therapeutic potency of novel peptides that could solve the resistance issues.

In Vitro and In Vivo Anti-Candida albicans Activity of a Scorpion-Derived Peptide

The increasing infection and drug resistance frequency has encouraged the exploration of new and effective anti-Candida albicans agents. In this study, CT-K3K7, a scorpion antimicrobial peptide derivative, effectively inhibit the growth of C. albicans. CT-K3K7 killed C. albicans cells in a dose-dependent manner, mainly by damaging the plasma membrane. CT-K3K7 could also disrupt the nucleus and interact with nucleic acid. Moreover, CT-K3K7 induced C. albicans cells necrosis via a reactive oxygen species (ROS)-related pathway. Furthermore, CT-K3K7 inhibited the hyphal and biofilm formation of C. albicans. In the mouse skin subcutaneous infection model, CT-K3K7 significantly prevented skin abscess formation and reduced the number of C. albicans cells recovered from the infection area. Taken together, CT-K3K7 has the potential to be a therapeutic for C. albicans skin infections.

Antimicrobial Activity of Short Analogues of the Marine Peptide EeCentrocin 1: Synthesis of Lipopeptides and Head-to-Tail Cyclic Peptides and Mechanism of Action Studies

We have synthesised a series of 12-residue analogues of a previously reported lead peptide (P6) developed from the heavy chain of the marine peptide EeCentrocin 1, isolated from the sea urchin Echinus esculentus. We optimised the lead peptide by increasing its net positive charge, its lipophilicity through N-terminal fatty acid acylation or incorporation of a Trp residue, and by synthesising head-to-tail cyclic peptides under pseudo-high-dilution conditions. All peptides were screened for antimicrobial and antifungal activity, and toxicity was determined against human red blood cells. The two most potent peptide analogues were the linear peptide P6-W6R8 and its head-to-tail cyclic analogue cP6-W6R8 displaying minimum inhibitory concentrations of 0.4-6.6 μM against Gram-positive and Gram-negative bacteria and 6.2-13 μM against fungi. All peptides showed low haemolytic activity except for two of the lipopeptides, in which haemolytic activity correlated with increasing acyl chain length. Mode of action studies using bacterial biosensor strains revealed a membrane disruptive effect of both the linear and the cyclic peptide. Overall, the results of our study demonstrated that relatively simple structural modifications could be successfully employed in the development of potent antimicrobial lead peptides derived from marine natural products.

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 .

The antibacterial activity and therapeutic potential of the amphibian-derived peptide TB_KKG6K

Antimicrobial peptides (AMPs) have great potential to be developed as topical treatments for microbial infections of the skin, including those caused by the gram-positive human pathogen Staphylococcus aureus. Among the AMPs, temporin B (TB) is of particular interest. This 13-amino-acid-long cationic peptide is secreted by the granular glands of the European frog Rana temporaria and represents a primary line of defense against invading pathogens. The objective of this study was to investigate the antibacterial efficacy and the mode of action of the synthetic TB analog, TB_KKG6K, in a drug-resistant clinical isolate of S. aureus and assess the peptide's tolerance and curative potential in an in vitro infection model using three-dimensional human epidermis equivalents (HEEs). The results revealed a high bactericidal efficacy of TB_KKG6K at low micromolar concentrations. The peptide perturbed the bacterial cell membrane integrity by permeabilization and depolarization. TB_KKG6K showed no toxicity in the invertebrate mini-host model Galleria mellonella and a high level of tolerance when topically applied in HEEs. Importantly, the therapeutic potential of TB_KKG6K was confirmed in HEEs infected with S. aureus. The topical application of TB_KKG6K significantly reduced the bacterial load and lowered the pro-inflammatory response in the infected HEEs. These findings reinforce the antibacterial potential and therapeutic efficacy of TB_KKG6K against S. aureus infection, particularly in the context of a cutaneous infection.IMPORTANCEThe emergence of multidrug-resistant bacteria has rendered the exploration of novel therapeutic treatment strategies a pivotal area of research. Among the most promising candidates are amphibian-derived antimicrobial peptides (AMPs), which are ideal for the development of novel drugs due to their multifaceted mode of action. Extensive studies have been conducted on these peptides over the last decade, resulting in the development of temporin B (TB) peptide analogs that have undergone modifications to their primary sequence. These modified analogs have demonstrated enhanced antibacterial and antifungal efficacy, while exhibiting reduced hemolytic activity. TB_KKG6K has the potential to be a promising candidate for topical treatments due to its small size and high antimicrobial activity against pathogens of the human skin. In particular, it demonstrated efficacy against Staphylococcus aureus, a skin commensal that can become an opportunistic pathogen, causing a range of infections from minor skin infections to life-threatening diseases such as bacteremia and sepsis.

Machine learning-driven discovery of antimicrobial peptides targeting the GAPDH-TPI protein-protein interaction in Schistosoma mansoni for novel antischistosomal therapeutics

Schistosomiasis, caused by Schistosoma mansoni, remains a significant public health burden, particularly in endemic regions with limited access to effective treatment. The emergence of resistance to praziquantel necessitates the urgent discovery of novel therapeutic targets. This study explores the potential of antimicrobial peptides (AMPs) as inhibitors of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and triose phosphate isomerase (TPI) protein-protein interaction (PPI) in S. mansoni, a crucial glycolytic pathway component essential for parasite survival. A machine learning-driven approach was employed to filter 3306 AMPs from the Antimicrobial Peptide Database (APD) based on physicochemical properties and predicted binding affinities. Eighteen peptides were selected based on desirable physicochemical attributes and further subjected to molecular docking using HADDOCK 2.4. The results identified AP02590 (-103.5 ± 2.7 kcal/mol) and AP02754 (-87.8 ± 1.0 kcal/mol) as the most promising inhibitors, exhibiting strong binding affinities and stable complex formation compared to the native GAPDH-TPI complex (-77.8 ± 17.2 kcal/mol). Molecular dynamics (MD) simulations confirmed the stability of these complexes, with lower root mean square deviation (RMSD) values (AP02590: ∼2.5 Å, AP02754: ∼3.0 Å) and reduced root mean square fluctuation (RMSF) of key interacting residues. Radius of gyration (Rg) analysis further indicated compact structural stability. MMGBSA analysis validated these findings, showing favourable binding free energies for AP02590 (-50.80 ± 0.90 kcal/mol) and AP02754 (-46.31 ± 0.83 kcal/mol), reinforcing their potential as lead compounds for antischistosomal drug development. These findings provide a foundation for further experimental validation of peptide-based inhibitors targeting metabolic pathways in S. mansoni.

Terminally Symmetric β-Turn Peptides for Multidrug-Resistant Bacterial Infections

Antimicrobial peptides (AMPs) are considered promising agents to solve the problem of antibiotic resistance due to their unique membrane-disruption mechanism. In this research, de novo terminally symmetric β-turn AMPs were designed by combining the β-turn sequences derived from Tritrpticin with alternately arranged cationic and hydrophobic amino acid sequences. The structure-activity relationship of the peptides was studied. Among the designed peptides, P-07 (KIKIKPWWWPKIKIK-NH2) exhibited potent antimicrobial activity against all the tested bacterial strains, showing the highest bacterial selectivity, relatively low cytotoxicity, high bactericidal efficiency, and low potential to induce bacterial resistance. The antimicrobial mechanisms of P-07 involving membrane-disruption and lipopolysaccharide-binding were proven. Moreover, the in vivo studies confirmed the wound-healing ability of P-07 using a mice bacteria-infected full-thickness wound model. Taken together, P-07 showed great promise in the treatment of multidrug-resistant bacterial infections.

Alkyl Tail Variation on Chalcone-Based Quaternary Pyridinium Salts as Rule-of-Thumb for Antimicrobial Activity

Aiming at developing a new class of quaternary pyridinium salts, the lead compound 1, characterized by a pyridine-3-yl chalcone framework, was rationally modified by inserting alkyl functions varying from 6 to 18 carbon units. Among the set, some valuable lead compounds were identified. Derivatives 4-6 were primarily active against Staphylococcus aureus and Candida albicans, respectively (MIC = 1.56 and 3.125 μM). In comparison, analogs 4 and 5 showed significant activities against Escherichia coli (MIC = 6.25 μM). Interestingly, the antimicrobial property of compounds 4-6, as well as their antibiofilm activity, occurred at lower concentrations than their cyto- and erythrocyte toxicities, thus ensuring a favorable safety profile. Structure-activity relationship analysis highlighted the critical role of the alkyl tail length in the antimicrobial activity, and optimal results were observed for moieties ranging from 10 to 14 carbon units. Molecular dynamics studies performed on 2 and 5 by modeling them on Gram-positive and Gram-negative membranes showed that the derivatives, upon diffusing across periodic boundary conditions, were able to intercalate into the microbial membranes. The difference in diffusion rates provides useful information to support the diverse antimicrobial potencies of the newly designed quaternary pyridinium salt.

Activity and Safety Optimization of Mesoricin: A Dual-Domain Antifungal Peptide from Mesorhizobium sp

Cryptococcus neoformans infections pose a significant global health threat. This study introduces mesoricin, a novel dual-domain antimicrobial peptide (AMP) scaffold derived from Mesorhizobium sp. identified using an in silico quantitative antifungal activity index (AFI). The peptide structure comprises an α-helix domain, which disrupts microbial membranes but exhibits highly hemolytic activity, and a β-sheet domain, which targets intracellular energy metabolism and resilient pathways. Rational design through α-helix domain removal and AFI-guided mutations yielded a mesoricin variant with enhanced antifungal activity and reduced cytotoxicity. The optimized mesoricin exhibited broad-spectrum antifungal activity against various Cryptococcus and Candida species (MIC 8-16 μg/mL) while maintaining high biosafety (IC50 > 128 μg/mL against human cell lines). Particularly, the variant demonstrated enhanced fungicidal effects at sub-MIC levels and superior biofilm control capabilities compared to the prototype peptide. These findings highlight mesoricins as a promising scaffold for AMP development targeting Cryptococcus infections.

Natural products chlorotonils exert a complex antibacterial mechanism and address multiple targets

Antimicrobial resistance is a threat to human health rendering current first-line antibiotics ineffective. New agents overcoming resistance mechanisms are urgently needed to guarantee successful treatment of human disease in the future. Chlorotonils, a natural product class with yet unknown mode of action, were shown to have broad-spectrum activity against multi-resistant Gram-positive bacteria and the malaria parasite Plasmodium falciparum, with promising activity and safety in murine infection models. Here, we report that chlorotonils can target the cell membrane, cell wall, and protein biosynthesis. They can be characterized by a rapid onset of action via interference with ion homeostasis leading to membrane depolarization, however, without inducing severe barrier failure or cellular lysis. Further characterization confirmed binding of chlorotonils to bacterial membrane lipids eventually leading to uncontrolled potassium transport. Additionally, we identified functional inhibition of the peptidoglycan biosynthesis protein YbjG and methionine aminopeptidase MetAP as secondary targets of chlorotonils.

The Role of Temperature and Subphase Components in Shaping Selected Physicochemical Properties of the Phosphatidylinositol Monolayer

Acne vulgaris is one of the most common skin diseases, and its development is closely linked to the overgrowth of the bacterium Cutibacterium acnes. More than half of the strains of this bacterium are resistant to antibiotics, which has prompted scientists to look for alternatives, such as antibacterial peptides, that can replace traditional drugs. Due to its antioxidant properties, ascorbic acid may be a promising ally in the treatment of acne. The aim of our study was to evaluate the effect of peptide (KWK)2-KWWW-NH2(P5) in the presence of ascorbic acid (AA) and its derivative (3-O-ethyl-L-ascorbic acid, EAA) on the stability and organization of phosphatidylinositol monolayers (PI) at temperatures of 25-35 °C. This study showed that the monolayers were in the expanded liquid state (35.28-49.95 mN/m) or in the transition between the expanded liquid and condensed phases (51.50-57.49 mN/m). Compression and decompression isotherms indicated the highest flexibility of the PI + P5 system, where the compression reversibility coefficient of isotherm values ranged from 80.59% to 97.77% and increased for each loop with increasing temperature. At 35 °C, the surface pressure of the monolayer in the PI + P5, PI + P5 + AA and PI + P5 + EAA systems changed less with time.

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.

Role of ygaD in mediating polymyxin B resistance in Bacillus subtilis via efflux mechanisms

OBJECTIVE

The aim of this study is to analyze the resistance function and mechanism of the putative ATP-binding cassette (ABC) transporter YgaD against polymyxin B in Bacillus subtilis.

METHODS

The interaction between the YgaD protein and the antimicrobial peptide polymyxin B was initially assessed using molecular docking and molecular dynamics simulation. Subsequently, resistance assays and intracellular polymyxin B content measurements were conducted on Bacillus subtilis with a knockout of the ygaD gene and on Escherichia coli with heterologous expression of the ygaD gene to validate the resistance function mediated by the YgaD protein and deduce its potential resistance mechanism.

RESULTS

The results demonstrated that the YgaD protein could form stable complexes with polymyxin B and facilitated its efflux from bacterial cells, thereby reducing its intracellular accumulation and conferring resistance to polymyxin B.

CONCLUSION

Our study revealed that YgaD regulates polymyxin B resistance in Bacillus subtilis through an efflux mechanism. These findings contribute to the understanding of microbial resistance mechanisms against antimicrobial peptides and provide a theoretical basis for the future design and development of antimicrobial drugs.

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.

Enhancing Antimicrobial Peptides from Frog Skin: A Rational Approach

Antimicrobial resistance is a global health threat, which has been worsened by the slow development of new antibiotics. The rational design of natural-derived antimicrobial peptides (AMPs) offers a promising alternative for enhancing the efficacy of AMPs and accelerating drug discovery. This paper describes the rational design of improved peptide derivatives starting from hylin-Pul3, a peptide previously isolated from the frog Boana pulchella, by optimizing its hydrophobicity, cationicity, and amphipathicity. In silico screening identified six promising candidates: dHP3-31, dHP3-50, dHP3-50.137, dHP3-50.190, dHP3-84, and dHP3-84.39. These derivatives exhibited enhanced activity against Gram-negative bacteria, emphasizing the role of cationicity and the strategic arginine incorporation. Hemolytic assays revealed the derivatives' improved selectivity, particularly for the derivatives with "imperfect amphipathicity". In fibroblast assays, dHP3-84 was well-tolerated, while dHP3-84.39 promoted cell proliferation. Antioxidant assays (ABTS assays) highlighted the Trp-containing derivatives' (dHP3-50.137, dHP3-31) significant activity. The lipid membrane interaction studies showed that hylin-Pul3 disrupts membranes directly, while dHP3-84.39, dHP3-50, and dHP3-50.137 promote vesicle aggregation. Conversely, dHP3-84 did not induce membrane disruption or aggregation, suggesting an intracellular mode of action. Machine learning models were effective in predicting bioactivity, as these predicted AMPs showed enhanced selectivity and potency. Among them, dHP3-84 demonstrated broad-spectrum potential. These findings highlight the value of rational design, in silico screening, and structure-activity studies in optimizing AMPs for therapeutic applications.

Amphiphilic lysine-based glycopeptides exert antibacterial effects on Pseudomonas aeruginosa

The development of new antibiotics with novel antimicrobial mechanisms and strategies has attracted considerable interest. Herein, three amphiphilic lysine-based glycopeptides (SA-l-Gal, OA-l-Gal and LOA-l-Gal) were developed, and their antibacterial activity and inhibition effects on biofilm formation on P. aeruginosa were studied. SA-l-Gal with a stearic acid group modification exhibited better antibacterial effects than the other lysine-based glycopeptides by damaging the bacterial membrane. Furthermore, SA-l-Gal could effectively reduce inflammation factor expression, enhance the formation of new blood vessels, and promote the healing of P. aeruginosa-infected mouse wounds. This result provides insights into the development of glycomimetic drugs against P. aeruginosa infection.

Antimicrobial peptide biological activity, delivery systems and clinical translation status and challenges

Antibiotic resistance is currently one of the most significant threats to global public health and safety. And studies have found that over the next 25 years, 39 million people will die directly and 169 million indirectly due to antibiotic-resistant diseases. Consequently, the development of new types of antimicrobial drugs is urgently needed. Antimicrobial peptides (AMPs) constitute an essential component of the innate immune response in all organisms. They exhibit a distinctive mechanism of action that endows them with a broad spectrum of biological activities, including antimicrobial, antibiofilm, antiviral, and anti-inflammatory effects. However, AMPs also present certain limitations, such as cytotoxicity, susceptibility to protein hydrolysis, and poor pharmacokinetic properties, which have impeded their clinical application. The development of delivery systems can address these challenges by modifying AMP delivery and enabling precise, controlled release at the site of infection or disease. This review offers a comprehensive analysis of the mechanisms of action and biological advantages of AMPs. and systematically evaluate how emerging drug delivery systems, such as nanoparticles and hydrogels, enhance the stability and bioavailability of AMPs, discussing both their strengths and limitations. Moreover, unlike previous reviews, this review highlight the most recent clinically approved AMP-based drugs and those currently in development, emphasizing the key challenges in translating these drugs into clinical practice. With these perspectives, it is hoped that this review will provide some insights into overcoming translational barriers and advancing AMPs drugs into clinical practice.

Membrane lipid composition directs the cellular selectivity of antimicrobial metallohelices

Two enantiomeric pairs of iron(ii) metallohelices, available as water-soluble, stable, and optically pure bimetallic complexes, differ principally in the length of the central hydrophobic region between two cationic domains, and have distinct activity and cell selectivity profiles against Gram-positive and Gram-negative microbes. The effects of dose concentration and temperature on levels of intracellular accumulation in E. coli and S. aureus, studied via isotopic labelling, indicate that the metallohelices enter the microbial cells via passive diffusion, whereupon (as previously determined) they act on intracellular targets. Whilst the metallohelices with the shorter central hydrophobic regions accumulate less readily than those with the longer hydrophobic bridge in both E. coli and S. aureus cells when incubated at the same concentration, an order of magnitude less is actually required per cell to inhibit growth in E. coli, hence they are more active. Furthermore, these more Gram-negative active compounds (with the shorter central hydrophobic region) are less toxic towards human APRE-19 mammalian cells and equine red blood cells. We hypothesise that these cell selectivities originate from the membrane composition. Dynamic light scattering and zeta potential measurements demonstrate that the more lipophilic metallohelices interact more strongly with the membrane-mimetic vesicles, notably in the charge-neutral mammalian model; thus the selectivity is not simply a result of electrostatic effects. For the less lipophilic metallohelices we observe that the binding affinity with the E. coli model vesicles is greater than with S. aureus vesicles, despite the lower negative surface charge, and this corresponds with the cellular accumulation data and the measured MICs. Specifically, the presence of membrane phosphatidylethanolamine (POPE) significantly increases the binding affinity of these metallohelices, and we postulate that a high proportion of such conical, non-lamellar phospholipids is important for metallohelix transport across the membrane. The metallohelices with the shorter hydrophobic bridge studied have a balance of charge and lipophilicity which allows selective cell entry in E. coli over mammalian cells, while the more lipophilic metallohelices are membrane promiscuous and unselective.

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.

Improving the antimicrobial activity of RP9 peptide through theoretical and experimental investigation

Future threats to humanity may stem from the rise of antimicrobial resistance, which has compromised the effectiveness of existing antibiotics. Antimicrobial peptides possess the ability to directly eliminate pathogens and cancer cells, generally without the development of resistance. Among these peptides is RP9 (RGSALTHLP), derived from the white blood cells of crocodiles. In this research, three mutations were initially designed: LR-mut (RGSALTHLR), KR-mut (RGSAKTHLR), and WP-mut (RGSAWTHLP). The physicochemical characteristics of these peptides were assessed, revealing that KR-mut exhibited the most favorable biophysical properties. Subsequently, twenty molecular dynamics simulations were conducted for all peptides in pure water and at four different octanol concentrations (30 %, 50 %, 70 %, and 100 %) to evaluate their biophysical attributes. The findings from the 4000 ns molecular dynamics simulations revealed that the KR-mut exhibited reduced values of RMSD, the radius of gyration, solvent accessible surface area, and RMSF, while simultaneously showing an increased number of hydrogen bonds and interactions with water molecules. This peptide also showed the lowest free energy of solvation and the highest solubility across various octanol concentrations compared to the other peptides. The results obtained from the biophysical assessments and molecular dynamics simulations were consistent, resulting in the conclusion that KR-mut is expected to exhibit superior antibacterial activity compared to both the other mutated peptides and the wild type peptides. These theoretical findings were validated through experimental minimum inhibitory concentration (MIC) tests on gram-negative Escherichia coli and gram-positive Staphylococcus aureus. The outcomes of this study suggest that molecular dynamics simulations can effectively predict changes in the bactericidal efficacy of peptides at varying octanol concentrations, potentially enhancing the speed and efficiency of antimicrobial peptide design while reducing associated costs.

Streptococcus salivarius and Ligilactobacillus salivarius: Paragons of Probiotic Potential and Reservoirs of Novel Antimicrobials

This review highlights several basic problems associated with bacterial drug resistance, including the decreasing efficacy of commercially available antimicrobials as well as the related problem of microbiome irregularity and dysbiosis. The article explains that this present situation is addressable through LAB species, such as Streptococcus salivarius and Ligilactobacillus salivarius, which are well established synthesizers of both broad- and narrow-spectrum antimicrobials. The sheer number of antimicrobials produced by LAB species and the breadth of their biological effects, both in terms of their bacteriostatic/bactericidal abilities and their immunomodulation, make them prime candidates for new probiotics and antibiotics. Given the ease with which several of the molecules can be biochemically engineered and the fact that many of these compounds target evolutionarily constrained target sites, it seems apparent that these compounds and their producing organisms ought to be looked at as the next generation of robust dual action symbiotic drugs.

The Role of Beta-Defensin 2 in Preventing Preterm Birth with Chorioamnionitis: Insights into Inflammatory Responses and Epithelial Barrier Protection

Antimicrobial peptides, such as beta-defensin 2 (BD2), are vital in controlling infections and immune responses. In this study, we investigated the expression and role of BD2 in the amniotic membrane and human amniotic epithelial cells (hAECs) from patients with preterm birth and chorioamnionitis, focusing on its regulation of inflammatory cytokines and its protective effect on the epithelial barrier. Our results show increased BD2 expression in chorioamnionitis, and Lipopolysaccharide (LPS)-induced inflammation increased BD2 release from hAECs in a dose- and time-dependent manner. BD2 treatment effectively modulated the inflammatory response by reducing pro-inflammatory cytokines (IL-6, IL-1β) and enhancing the release of the anti-inflammatory cytokine IL-10. Additionally, BD2 helps preserve epithelial barrier integrity by restoring E-cadherin expression and reducing Snail expression in inflamed hAECs. In an LPS-induced preterm birth mouse model, BD2 treatment delayed preterm delivery and reduced inflammatory cytokine levels. These results suggest that BD2 plays a protective role in preventing preterm birth by regulating inflammation and maintaining epithelial barrier function, highlighting its therapeutic potential for inflammation-related preterm birth.

A Novel Hepcidin Isoform Jd-Hep from the Sin Croaker Johnius dussumieri (Cuvier, 1830): Recombinant Expression and Insights into the Antibacterial Property and Modes of Action

Hepcidin is a cysteine-rich antimicrobial peptide that plays an important role in fish immunity. In the current study, we report a novel isoform of hepcidin (Jd-Hep) from Sin croaker, Johnius dussumieri, with an open reading frame (ORF) of 258 nucleotide bases that encodes 85 amino acids containing a signal peptide (24 amino acids), a prodomain (35 amino acids) and a biologically active mature peptide (26 amino acids). Phylogenetic tree analysis showed that J. dussumieri hepcidin belonged to the HAMP2 cluster of hepcidin. The tissue distribution showed that the expression of hepcidin was highest in the liver in wild-caught J. dussumieri. The mature peptide mJd-Hep was recombinantly expressed in a prokaryotic host, E. coli Rosetta-gami™B (DE3) pLysS cells, and the peptide was isolated and purified. The recombinant peptide, rJd-Hep, exhibited notable antibacterial activity against aquatic pathogens such as Aeromonas hydrophila, Vibrio parahaemolyticus, Vibrio harveyi, Vibrio alginolyticus, Vibrio proteolyticus, and Vibrio fluvialis. The mode of action of the peptide was proven to be membrane-based (pore formation and depolarization). The rJd-Hep was found to be non-hemolytic to hRBCs and non-cytotoxic to the mammalian cell line. The peptide showed 85% growth inhibition of cancer cell line, MCF-7. These findings expand our knowledge of the potential application of hepcidin in aquaculture as a therapeutic agent.

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.

Microbial production systems and optimization strategies of antimicrobial peptides: a review

Antibiotic resistance has become a public safety issue of the twenty-first century, posing a growing threat and drawing increased attention. Compared to traditional antibiotics, antimicrobial peptides (AMPs), as naturally produced small peptides, can target multiple pathways within pathogens and render them less prone to developing resistance. This makes them promising alternatives to antibiotics. However, traditional chemical synthesis methods face challenges, such as high costs, low yields, and poor stability, limiting the large-scale industrial production of AMPs. Despite extensive research to improve AMP production efficiency, issues such as low yields and complex extraction processes continue to pose significant barriers to commercial application. Therefore, there is an urgent need for new biosynthesis strategies and optimization methods to enhance AMP production efficiency and quality. This review summarizes the sources, classification, mechanisms of action and recent advances in the microbial synthesis of AMPs. It also explores innovative production methods, including recombinant microbial expression systems, fusion tags, codon optimization, tandem multimer expression, and hybrid peptide expression. Furthermore, we review the applications of gene editing technologies and artificial intelligence in AMP production, providing new perspectives and strategies for efficient, large-scale AMP production.

Failure or future? Exploring alternative antibacterials: a comparative analysis of antibiotics and naturally derived biopolymers

The global crisis of antimicrobial resistance (AMR) is escalating due to the misuse and overuse of antibiotics, the slow development of new therapies, and the rise of multidrug-resistant (MDR) infections. Traditional antibiotic treatments face limitations, including the development of resistance, disruption of the microbiota, adverse side effects, and environmental impact, emphasizing the urgent need for innovative alternative antibacterial strategies. This review critically examines naturally derived biopolymers with intrinsic (essential feature) antibacterial properties as a sustainable, next-generation alternative to traditional antibiotics. These biopolymers may address bacterial resistance uniquely by disrupting bacterial membranes rather than cellular functions, potentially reducing microbiota interference. Through a comparative analysis of the mechanisms and applications of antibiotics and antibacterial naturally derived biopolymers, this review highlights the potential of such biopolymers to address AMR while supporting human and environmental health.

Molecular insights into the differential membrane targeting of maximin 1 in prokaryotic and eukaryotic cells

Antimicrobial resistance is a pressing global health concern, underscoring the need for alternative treatments. Antimicrobial peptides (AMPs) have shown promise in this regard, with maximin 1 being a cationic, amphipathic AMP possessing antibacterial, antifungal, and antiviral activities with low hemolytic activity. In this study, we used molecular dynamics simulation to investigate the molecular basis for membrane selectivity of Maximin 1. By studying interactions between maximin 1 and different models of prokaryotic (anionic) and eukaryotic (zwitterionic) membranes, we found that Maximin 1 interacts more strongly with the prokaryotic membrane due to electrostatic attraction, while it weakly interacts with the zwitterionic eukaryotic membrane. Our simulations also revealed that Gly-1, Lys-5, Lys-11, Lys-15, and Lys-19 were identified to play a crucial role in the adsorption of maximin unto the prokaryotic membrane surface. The alpha-helical nature of the peptide, in addition to its amphipathic nature, was necessary for the adsorption of the peptide onto the surface of the prokaryotic membrane. Interestingly, the later transition of the alpha helix into a random coil was crucial in penetrating the prokaryotic membrane while hindering interactions with the eukaryotic membrane. Residues in the middle region of the peptide (residues 9-16) were also responsible for permeating the prokaryotic membrane over the eukaryotic membrane. These findings shed light on the peptide's selective targeting of bacterial membranes over human cell membranes and could inform the design of more effective AMPs.Communicated by Ramaswamy H. Sarma.

Characterization of antimicrobial properties of TroH2A-29 peptide from golden pompano (Trachinotus ovatus)

Antimicrobial peptides (AMPs) are small, potent molecules that serve as a crucial first line of defense across a wide range of organisms, including fish. In this study, we investigated the antimicrobial properties of a novel peptide, spanning residues 52 to 80 of the full-length histone H2A protein, comprising a total of 29 amino acids. This peptide, designated as Histone H2A-29 (TroH2A-29), was derived from the golden pompano (Trachinotus ovatus) and evaluated for its activity against both Gram-positive bacteria, Lactococcus garvieae and Staphylococcus epidermidis, and Gram-negative bacteria, Vibrio alginolyticus and Vibrio harveyi. The expression of TroH2A in the intestines, liver, and gills of T. ovatus was significantly upregulated after bacterial infections with L. garvieae and V. harveyi. The highest expression levels were observed at 48 h post-infection in the intestines and at different time points in the liver and gills. TroH2A-29 exhibited a high hydrophobic ratio (51 %) and formed an α-helical structure, suggesting its potential as an antimicrobial agent. Notably, TroH2A-29 induced significant agglutination of all four bacterial species in the presence of Ca2⁺. TroH2A-29 demonstrated bactericidal effects against L. garvieae, V. harveyi, and V. alginolyticus, with a MIC50 of 60 μM. However, it showed no antibacterial activity against S. epidermidis. Transmission electron microscopy (TEM) revealed that TroH2A-29 caused morphological damage to the bacterial cells, including cell collapse in L. garvieae and shrinkage in V. alginolyticus and V. harveyi. No morphological changes were observed in S. epidermidis. Membrane permeability assays showed that TroH2A-29 increased membrane disruption in L. garvieae, V. harveyi, and V. alginolyticus, but had little effect on S. epidermidis. Additionally, TroH2A-29 caused membrane depolarization in all tested bacterial strains. These findings highlight the potential of TroH2A-29 as a novel antimicrobial peptide with selective bactericidal properties.

Research Progress of Bioactive Peptides in Improving Type II Diabetes

Type II diabetes mellitus (T2DM) is a prevalent, long-standing metabolic condition marked by the body's reduced response to insulin and inadequate insulin production, impacting a significant portion of the global population. Research has demonstrated that bioactive peptides play a crucial role in reducing blood sugar levels, enhancing insulin sensitivity, balancing lipid metabolism, and combating inflammation. These peptides also contribute to the enhancement of pancreatic islet function, lowering systemic inflammation by influencing various molecular signaling pathways. This paper provides an overview of recent advancements and potential applications of bioactive peptides in addressing T2DM. It highlights the diverse impacts of bioactive peptides sourced from different origins in combating diabetes. This comprehensive review offers theoretical substantiation and novel insights to support the future clinical utilization and exploration of bioactive peptides for T2DM management.

Inflammation and response to bacterial infection as potential drivers of equine odontoclastic tooth resorption and hypercementosis: A proteomics insight

BACKGROUND

Equine dental diseases significantly impact a horse's overall health, performance and quality of life. They can result in secondary infections and digestive disturbances, potentially leading to colic. A recently described disease affecting the incisors of horses is equine odontoclastic tooth resorption and hypercementosis (EOTRH). Understanding EOTRH is crucial for early diagnosis, effective management and prevention of its severe consequences.

OBJECTIVES

To determine proteomic differences in incisor cementum in horses with and without clinical EOTRH.

STUDY DESIGN

Comparative and observational clinical study.

METHODS

Teeth were extracted (N = 5) and cementum was isolated using a diamond wire. Proteins were extracted using an optimised sequential workflow, and trypsin was digested for mass spectrometry. Protein identification and label-free quantification were undertaken.

RESULTS

In total 1149 unique proteins were detected in cementum across all samples. We identified four proteins exclusively in EOTRH-affected cementum. EOTRH samples showed a higher heterogeneity than healthy samples. In total, 54 proteins were increased in EOTRH, and 64 proteins were reduced (adjusted p-value <0.05). Inflammatory proteins, such as cathepsin G (p = 0.004), neutrophil elastase (p = 0.003), bactericidal permeability-increasing protein (p = 0.002), azurocidin (p = 0.003) and lactotransferrin (p = 0.002) were all increased in EOTRH. Pathway analysis revealed that antimicrobial peptides (Z score 2.65, p = 1.93E-09) and neutrophil degranulation (Z-score 1.89, p = 1.7E-04) were commonly up-regulated canonical pathways.

MAIN LIMITATIONS

The sample size was limited. Lack of age-matched healthy controls.

CONCLUSION

EOTRH leads to biochemical changes within the cementum proteome, which are important in explaining the physiological changes occurring in disease. Differentially abundant proteins may represent promising biomarkers for earlier disease detection and the establishment of a cell-based model could provide further insight into the role these proteins play in hypercementosis and resorption.

Bacterial proteome microarray technology in biomedical research

Bacterial proteome microarrays are high-throughput, adaptable tools that allow the simultaneous investigation of thousands of proteins from various bacterial species. These arrays are used to explore bacterial pathogenicity, pathogen-host interactions, and clinical diseases. Recent advancements have expanded their application to profiling human antibodies, identifying biomarkers for infectious and autoimmune diseases, and studying antimicrobial peptides (AMPs). This review highlights significant outcomes from recent studies, focusing on their diverse applications in biomedical research. Notable findings include the identification of novel antigens and diagnostic markers for gastrointestinal infections, autoimmune diseases, and mental health disorders. This technology promises to further elucidate the complex relationship between bacteria and their hosts, ultimately informing the development of new diagnostic, therapeutic, and preventive strategies.

Unveiling novel antimicrobial peptides from the ruminant gastrointestinal microbiomes: A deep learning-driven approach yields an anti-MRSA candidate

INTRODUCTION

Antimicrobial peptides (AMPs) present a promising avenue to combat the growing threat of antibiotic resistance. The ruminant gastrointestinal microbiome serves as a unique ecosystem that offers untapped potential for AMP discovery.

OBJECTIVES

The aims of this study are to develop an effective methodology for the identification of novel AMPs from ruminant gastrointestinal microbiomes, followed by evaluating their antimicrobial efficacy and elucidating the mechanisms underlying their activity.

METHODS

We developed a deep learning-based model to identify AMP candidates from a dataset comprising 120 metagenomes and 10,373 metagenome-assembled genomes derived from the ruminant gastrointestinal tract. Both in vivo and in vitro experiments were performed to examine and validate the antimicrobial activities of the AMP candidates that were selected through bioinformatic analysis and subsequently synthesized chemically. Additionally, molecular dynamics simulations were conducted to explore the action mechanism of the most potent AMP candidate.

RESULTS

The deep learning model identified 27,192 potential secretory AMP candidates. Following bioinformatic analysis, 39 candidates were synthesized and tested. Remarkably, all synthesized peptides demonstrated antimicrobial activity against Staphylococcus aureus, with 79.5% showing effectiveness against multiple pathogens. Notably, Peptide 4, which exhibited the highest antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), confirmed this effect in a mouse model with wound infection, exhibiting a low propensity for resistance development and minimal cytotoxicity and hemolysis towards mammalian cells. Molecular dynamics simulations provided insights into the mechanism of Peptide 4, primarily its ability to disrupt bacterial cell membranes, leading to cell death.

CONCLUSION

This study highlights the power of combining deep learning with microbiome research to uncover novel therapeutic candidates, paving the way for the development of next-generation antimicrobials like Peptide 4 to combat the growing threat of MRSA would infections. It also underscores the value of utilizing ruminant microbial resources.

Antimicrobial Peptides: A Promising Alternative to Conventional Antimicrobials for Combating Polymicrobial Biofilms

Polymicrobial biofilms adhere to surfaces and enhance pathogen resistance to conventional treatments, significantly contributing to chronic infections in the respiratory tract, oral cavity, chronic wounds, and on medical devices. This review examines antimicrobial peptides (AMPs) as a promising alternative to traditional antibiotics for treating biofilm-associated infections. AMPs, which can be produced as part of the innate immune response or synthesized therapeutically, have broad-spectrum antimicrobial activity, often disrupting microbial cell membranes and causing cell death. Many specifically target negatively charged bacterial membranes, unlike host cell membranes. Research shows AMPs effectively inhibit and disrupt polymicrobial biofilms and can enhance conventional antibiotics' efficacy. Preclinical and clinical research is advancing, with animal studies and clinical trials showing promise against multidrug-resistant bacteria and fungi. Numerous patents indicate increasing interest in AMPs. However, challenges such as peptide stability, potential cytotoxicity, and high production costs must be addressed. Ongoing research focuses on optimizing AMP structures, enhancing stability, and developing cost-effective production methods. In summary, AMPs offer a novel approach to combating biofilm-associated infections, with their unique mechanisms and synergistic potential with existing antibiotics positioning them as promising candidates for future treatments.

The Sensitivity of Opportunistic Bacteria to Blood Serum Low-Molecular Fraction Containing Antimicrobial Peptides and Proteins

We studied the sensitivity of clinically significant (opportunistic) bacteria to blood serum fraction with a molecular weight <100 kDa containing antimicrobial peptides and proteins. The degree of damage to cytoplasmic membranes of bacterial cells was assessed by a spectrophotometric method. A total of 129 bacterial isolates belonging to 46 species, 19 genera, 13 families, 8 orders, 4 classes, and 3 types were studied. The mean sensitivity varied from -5.2 to 36.6%. The sensitivity depends on the structure of bacterial cell wall: higher sensitivity was demonstrated by taxonomic ranks related to gram-negative bacteria (median 19.1%) and lower values were observed in gram-positive bacteria (median 9.3%) (p<0.01). Among all orders, Lactobacilliales showed the lowest sensitivity (3.6%). Ranking of the studied species by their sensitivity showed that 7 of the first 15 species with sensitivity >19% are among to the leading causative agents of sepsis.

In vitro Antileishmanial Activity and In silico Molecular Modeling Studies of Novel Analogs of Dermaseptins S4 and B2

BACKGROUND

Leishmaniasis is responsible for approximately 65,000 annual deaths. Various Leishmania species are the predominant cause of visceral, cutaneous, or mucocutaneous leishmaniasis, affecting millions worldwide. The lack of a vaccine, emergence of resistance, and undesirable side effects caused by antileishmanial medications have prompted researchers to look for novel therapeutic approaches to treat this disease. Antimicrobial peptides (AMPs) offer an alternative for promoting the discovery of new drugs.

METHODS

In this study, we detail the synthesis process and investigate the antileishmanial activity against Leishmania (Viannia) braziliensis for peptides belonging to the dermaseptin (DS) family and their synthetic analogs. The MTT assay was performed to investigate the cytotoxicity of these peptides on the murine macrophage cell line RAW 264.7. Subsequently, we performed molecular modeling analysis to explore the structure-function correlation of the derivatives interacting with the parasitic membrane.

RESULTS

All examined derivatives displayed concentration-dependent antileishmanial effect at low concentrations. Their effectiveness varied according to the peptide's proprieties. Notably, peptides with higher levels of charge demonstrated the most pronounced activities. Cytotoxicity assays showed that all the tested peptides were not cytotoxic compared to the tested conventional drug. The structure-function relationships demonstrated that the charged N-terminus could be responsible for the antileishmanial effect observed on promastigotes.

CONCLUSION

Collectively, these results propose that dermaseptins (DS) might offer potential as promising candidates for the development of effective antileishmanial therapies.

Honeybee defense mechanisms: Role of honeybee gut microbiota and antimicrobial peptides in maintaining colony health and preventing diseases

Honeybees play a vital role in pollination and the maintenance of ecosystem biodiversity, making their health and well-being crucial for agriculture and environmental sustainability. Bee health is modulated by symbiotic microorganisms colonizing the gut in balanced proportions. Studies have demonstrated that these beneficial bacteria have the capacity to enhance the immune system of honey bees, having substantial impact on regulating their immunological responses and hence aiding in defending against pathogenic illnesses. Another important aspect of honeybee health is their innate immune system that is related to their ability to synthesize antimicrobial peptides (AMP). AMPs, the small, cationic peptides are the humoral effector molecules that are synthesized in the hemolymph of the insects after being exposed to microbial infectious agents. A number of honeybee's gut microbiota especially Lactic Acid Bacteria (LAB), are known to regulate the production of several AMPs and hence are able to provide protection to these insects against a number of disease agents by modulating their innate immune response via induction of the AMPs genes. These AMPs mainly produced by adult workers are an important and integral part of an insect's immune response. Several AMPs namely apidaecins, abaecins, hymenoptaecins and defensins produced in the adult honeybee, hold the ability to control or prevent a number of diseases in these pollinator insects.

Antifungal peptides from living organisms

In the post-COVID-19 era, people are increasingly concerned about microbial infections, including fungal infections that have risen in recent years. However, the currently available antifungal agents are rather limited. Worse still, the widespread use of the antifungal agents has caused the emergence of antifungal resistance in Candida, Cryptococcus, and Aspergillus species. Therefore, the development of novel antifungals is urgently needed. Antimicrobial peptides (AMPs), as components of the first-line defense of the host, are found to exhibit broad antimicrobial activity against bacteria, fungi, parasites, viruses, and protozoa. AMPs with antifungal activity are specifically referred to as antifungal peptides (AFPs). AFPs are currently regarded as the most promising alternative to conventional antifungal agents due to the fact that they are highly selective and less prone to facilitate the selection of drug resistance. In this review, we present an overview of the origin and classification of natural AFPs as well as their modes of action. Additionally, the production of natural, semisynthetic, and synthetic AFPs with a view to greater levels of exploitation is discussed. Finally, we evaluate the current and potential applications of AFPs in clinics and in the food industry.

Zn(II) coordination influences the secondary structure, but not antimicrobial activity of the N-terminal histatin 3 hydrolysis product

The relationship between the coordination chemistry and antimicrobial activity of Zn(II) and Cu(II)-bound histatins, salivary antimicrobial peptides, remains enigmatic. We focus on metal complexes of histatin 3 and its two products of hydrolysis: histatin 4 and its N-terminal fragment (histatin 3-4). The thermodynamic stability of these complexes is quite expected - the binding of Cu(II) via the ATCUN motif results in the formation of very stable complexes. In histatin-Zn(II) complexes, the {2Nim} type of coordination dominates, with polymorphic binding sites observed for histatin 3-4 and 5-8, resulting in their low thermodynamic stability compared to the complexes of histatin 3, 4, 5 and 8 with Zn(II), in which we observe a {2Nim, O-} type of coordination. Histatin 3, 3-4 and 4 have greater activity against Gram-positive bacteria than against Gram-negative ones, and Cu(II) or Zn(II) binding can, in some cases, moderately increase the antimicrobial activity of the native histatin 3 and 4, but not the remaining 3-4 fragment. The most probable reason for the metal-enhanced antimicrobial activity is, in this case, a local change of charge, while the chemically fascinating metal binding induced structural changes do not result in a change of biological activity. Neither histatin 3-4, the N-terminal fragment of histatin 3, which remains in solution after cleavage, nor its metal complexes have any antimicrobial activity, but histatin 3-4 presents intriguing Zn(II)-induced structural behavior, changing its secondary structure, with a tendency to form an α-helix.

Structure-Activity Relationships in Supramolecular Hosts Targeting Bacterial Phosphatidylethanolamine (PE) Lipids

The World Health Organization has described the antimicrobial resistance crisis as one of the top ten global public health threats. New antimicrobial agents that can fight infections caused by antimicrobial resistant pathogens are therefore needed. A potential strategy is the development of small molecules that can selectively interact with bacterial membranes (or membranes of other microbial pathogens), and thereby rapidly kill the bacteria. Here, we report the structure-activity relationship within a group of 22 compounds that were designed to bind the bacterial lipid phosphatidylethanolamine (PE). Liposome-based studies reveal that the lipophilicity of the compounds has the strongest effect on both the affinity and selectivity for PE. The best results were obtained for compounds with logP≈3.75, which showed a 5x-7x selectivity for bacterial PE lipids over human PC (phosphatidylcholine) lipids. Furthermore, these compounds also showed potent antibacterial activity against the Gram-positive bacterium B. cereus, with minimum inhibitory concentrations (MICs) below 10 μM, a concentration where they showed minimal hemolytic activity against human red blood cells. These results not only show the possibility of PE-binding small molecules to function as antibiotics, but also provide guidelines for the development of compounds targeting other types of biologically relevant membrane lipids.

Antimicrobial Peptides: A Promising Solution to the Rising Threat of Antibiotic Resistance

The demand for developing novel antimicrobial drugs has increased due to the rapid appearance and global spread of antibiotic resistance. Antimicrobial peptides (AMPs) offer distinct advantages over traditional antibiotics, such as broad-range efficacy, a delayed evolution of resistance, and the capacity to enhance human immunity. AMPs are being developed as potential medicines, and current computational and experimental tools aim to facilitate their preclinical and clinical development. Structural and functional constraints as well as a more stringent regulatory framework have impeded clinical translation of AMPs as possible therapeutic agents. Although around four thousand AMPs have been identified so far, there are some limitations of using these AMPs in clinical trials due to their safety in the host and sometimes limitations in the biosynthesis or chemical synthesis of some AMPs. Overcoming these obstacles may help to open a new era of AMPs to combat superbugs without using synthetic antibiotics. This review describes the classification, mechanisms of action and immune modulation, advantages, difficulties, and opportunities of using AMPs against multidrug-resistant pathogens and highlights the need and priorities for creating targeted development strategies that take into account the most cutting-edge tools currently available. It also describes the barriers to using these AMPs in clinical trials.

Boosting the antibacterial potential of a linear encrypted peptide in a Kunitz-type inhibitor (ApTI) through physicochemical-guided approaches

Bacterial resistance has become a serious public health problem in recent years, thus encouraging the search for new antimicrobial agents. Here, we report an antimicrobial peptide (AMP), called PEPAD, which was designed based on an encrypted peptide from a Kunitz-type plant peptidase inhibitor. PEPAD was capable of rapidly inhibiting and eliminating numerous bacterial species at micromolar concentrations (from 4μM to 10 μM), with direct membrane activity. It was also observed that the peptide can act synergistically with ciprofloxacin and showed no toxicity in the G. mellonella in vivo assay. Circular dichroism assays revealed that the peptide's secondary structure adopts different scaffolds depending on the environment in which it is inserted. In lipids mimicking bacterial cell membranes, PEPAD adopts a more stable α-helical structure, which is consistent with its membrane-associated mechanism of action. When in contact with lipids mimicking mammalian cells, PEPAD adopts a disordered structure, losing its function and suggesting cellular selectivity. Therefore, these findings make PEPAD a promising candidate for future antimicrobial therapies with low toxicity to the host.

De novo design of Na+-activated lipopeptides with selective antifungal activity: A promising strategy for antifungal drug discovery

In recent years, invasive fungal infections have posed a significant threat to human health, particularly due to the limited availability of effective antifungal medications. This study responds to the urgent need for powerful and selective antifungal agents by designing and synthesizing a series of lipopeptides with lipoylation at the N-terminus of the antimicrobial peptide I6. Compared to the parent peptide I6, lipopeptides exhibited selective antifungal efficacy in the presence of Na+. Among the variants tested, C8-I6 emerged as the most effective, with an average effective concentration of 5.3 μM against 12 different fungal species. C8-I6 combated fungal infections by disrupting both cytoplasmic and mitochondrial membranes, impairing the proton motive force, generating reactive oxygen species, and triggering apoptosis in fungal cells. Importantly, C8-I6 exhibited minimal hemolysis and cytotoxicity while effectively inhibiting fungal biofilm formation. In vivo experiments further validated the safety and therapeutic potential of C8-I6 in treating fungal skin infections. These findings underscore the significance of lipoylation in enhancing the efficacy of antimicrobial peptides, positioning C8-I6 as a promising candidate in fighting against drug-resistant fungal infections.

Molecular Identification and Characterization of Hevein Antimicrobial Peptide Genes in Two-Row and Six-Row Cultivars of Barley (Hordeum vulgare L.)

Heveins are one of the most important groups of plant antimicrobial peptides. So far, various roles in plant growth and development and in response to biotic and abiotic stresses have reported for heveins. The present study aimed to identify and characterize the hevein genes in two-row and six-row cultivars of barley. In total, thirteen hevein genes were identified in the genome of two-row and six-row cultivars of barley. The identified heveins were identical in two-row and six-row cultivars of barley and showed a high similarity with heveins from other plant species. The hevein coding sequences produced open reading frames (ORFs) ranged from 342 to 1002 bp. Most of the identified hevein genes were intronless, and the others had only one intron. The hevein ORFs produced proteins ranged from 113 to 333 amino acids. Search for conserved functional domains showed CBD and LYZ domains in barley heveins. All barley heveins comprised extracellular signal peptides ranged from 19 to 35 amino acids. The phylogenetic analysis divided barley heveins into two groups. The promoter analysis showed regulatory elements with different frequencies between two-row and six-row cultivars. These cis-acting elements included elements related to growth and development, hormone response, and environmental stresses. The expression analysis showed high expression level of heveins in root and reproductive organs of both two-row and six-row cultivars. The expression analysis also showed that barley heveins is induced by both biotic and abiotic stresses. The results of antimicrobial activity prediction showed the highest antimicrobial activity in CBD domain of barley heveins. The findings of the current study can improve our knowledge about the role of hevein genes in plant and can be used for future studies.

A novel cathelicidin TS-CATH derived from Thamnophis sirtalis combats drug-resistant gram-negative bacteria in vitro and in vivo

Antimicrobial peptides are promising therapeutic agents for treating drug-resistant bacterial disease due to their broad-spectrum antimicrobial activity and decreased susceptibility to evolutionary resistance. In this study, three novel cathelicidin antimicrobial peptides were identified from Thamnophis sirtalis, Balaenoptera musculus, and Lipotes vexillifer by protein database mining and sequence alignment and were subsequently named TS-CATH, BM-CATH, and LV-CATH, respectively. All three peptides exhibited satisfactory antibacterial activity and broad antibacterial spectra against clinically isolated E. coli, P. aeruginosa, K. pneumoniae, and A. baumannii in vitro. Among them, TS-CATH displayed the best antimicrobial/bactericidal activity, with a rapid elimination efficiency against the tested drug-resistant gram-negative bacteria within 20 min, and exhibited the lowest cytotoxicity toward mammalian cells. Furthermore, TS-CATH effectively enhanced the survival rate of mice with ceftazidime-resistant E. coli bacteremia and promoted wound healing in meropenem-resistant P. aeruginosa infection. These results were achieved through the eradication of bacterial growth in target organs and wounds, further inhibiting the systemic dissemination of bacteria and the inflammatory response. TS-CATH exhibited direct antimicrobial activity by damaging the inner and outer membranes, resulting in leakage of the bacterial contents at super-MICs. Moreover, TS-CATH disrupted the bacterial respiratory chain, which inhibited ATP synthesis and induced ROS formation, significantly contributing to its antibacterial efficacy at sub-MICs. Overall, TS-CATH has potential for use as an antibacterial agent.