The revitalization of antimicrobial peptides in the resistance era

Isolation and characterization of quinoa antimicrobial peptides and its effect on the microbial diversity of fresh apple juice

This study developed antimicrobial peptides (AMPs) from quinoa with high antibacterial activity and stability by mixed-bacteria fermentation. Furthermore, among 9 peptide fractions purified by membrane separation and chromatography, F1 could effectively inhibit the growth and propagation of bacterial microorganisms in apple juice. Subsequently, F1 identified LC-MS/MS as 95 peptides, molecular weights 494.25 Da to 1253.55 Da, notably, AGAAPE peptide (556.25 Da), negatively charged (-1), highly hydrophobic (50 %), with significant inhibitory effects on both Escherichia coli and Staphylococcus aureus (MIC 5 mg/mL). The antimicrobial mechanism of AGAAPE was determined to damage membrane through hydrogen-bond and hydrophobic interactions, resulting in leakage of intramembrane substances and inhibition of intracellular ATPase activity. Moreover, AGAAPE was pH resistant (pH 4-12), thermally stable (121 °C, 30 min), resistant to salt ion interference (Na+, Ca2+), and protease hydrolysis resistant (neutral protease, pepsin, trypsin). Overall, identifying AMPs from quinoa provides a promising new approach for fresh juice preservation.

Control of Postharvest Green Mold in Citrus by the Antimicrobial Peptide BP15 and Its Lipopeptides

This study examined the efficacy and mechanisms of action of the antimicrobial peptide BP15 and its lipopeptides, HBP15 and LBP15, against Penicillium digitatum, the primary causative agent of green mold in citrus fruits. The findings revealed that all three antimicrobial peptides markedly inhibited the spore germination and mycelial growth of P. digitatum, with minimum inhibitory concentrations (MICs) of 3.12 μM for BP15, HBP15, and LBP15. The peptides induced morphological alterations in hyphae and elevated intracellular Sytox Green (SG) fluorescence signals, which is indicative of increased cell membrane permeability and disruption. This membrane damage was further supported by the heightened extracellular conductivity and the release of intracellular nucleic acid and protein. A gel retardation assay demonstrated that the peptides showed significant DNA binding and retardation effects. Furthermore, the peptides exhibited significantly lower hemolytic activity (p < 0.05) compared to commercial prochloraz in normal mammalian erythrocytes (sheep erythrocytes) at the tested concentrations. Therefore, BP15 and its lipopeptides, HBP15 and LBP15, show potential as effective agents for preventing green mold in citrus fruits.

Membrane alteration, anti-virulence properties and metabolomic perturbation of a chionodracine-derived antimicrobial peptide, KHS-Cnd, on two bacteria models

Antarctic fishes, living in an extreme environment and normally exposed to pathogens, are a promising source of antimicrobial peptides (AMPs). These are emerging as next-generation drugs due to their activity against multidrug resistant (MDR) bacteria. To infect hosts, beyond intrinsic/acquired resistance, MDR species also use virulence factors such as protease secretion. Hence, AMPs targeting virulence factors could represent a novel strategy to counteract the antimicrobial resistance (AMR). In this paper, we focused on a mutant peptide, named KHS-Cnd, that was obtained from the scaffold of the chionodracine (Cnd), a natural peptide identified in the icefish Chionodraco hamatus. We studied different effects caused by the peptide interaction with the cell membrane of two model bacteria, E. coli and B. cereus. First, we investigated its membranolytic activity revealing that the peptide action is more evident on E. coli, with a 69 % uptake of the used dye at 3 μM, whereas for B. cereus we found only a 65 % uptake at 6 μM. Successively, we determined the impact of this lysis on total protein concentration in the medium and an increase was estimated for both bacteria (84 % after 1 h for E. coli and 90 % for B. cereus, respectively). Moreover, we evaluated the changes in the proteolytic activity of the supernatant, that is an important aspect of bacterial resistance, showing that there was a significant reduction for both bacteria, although at higher level in the case of E. coli. The membranolytic activity was evidenced also morphologically with TEM analysis and a different alteration was evidenced for the two bacteria. Moreover, NMR metabolomics analysis showed that peptide induces changes in E. coli and B. cereus extracellular metabolites especially at the higher tested concentrations: this metabolic variation could be used as a fingerprinting of the peptide action on bacteria physiology due to its interaction with cell wall. Finally, we determined the KHS-Cnd cytotoxicity on human primary cell lines to verify its selectivity toward bacterial cell membranes and we found low toxicity until a concentration of 5 μM. Considering that the peptide exerts both membranolytic and anti-virulence activity on E. coli at 1.5 μM, we confirmed the interesting potential of this AMP as a new drug to counteract AMR.

A review on the diversity of antimicrobial peptides and genome mining strategies for their prediction

Antibiotic resistance has become one of the most serious threats to human health in recent years. In response to the increasing microbial resistance to the antibiotics currently available, it is imperative to develop new antibiotics or explore new approaches to combat antibiotic resistance. Antimicrobial peptides (AMPs) have shown considerable promise in this regard, as the microbes develop low or no resistance against them. The discovery and development of AMPs still confront numerous obstacles such as finding a target, developing assays, and identifying hits and leads, which are time-consuming processes, making it difficult to reach the market. However, with the advent of genome mining, new antibiotics could be discovered efficiently using tools such as BAGEL, antiSMASH, RODEO, etc., providing hope for better treatment of diseases in the future. Computational methods used in genome mining automatically detect and annotate biosynthetic gene clusters in genomic data, making it a useful tool in natural product discovery. This review aims to shed light on the history, diversity, and mechanisms of action of AMPs and the data on new AMPs identified by traditional as well as genome mining strategies. It further substantiates the various phases of clinical trials for some AMPs, as well as an overview of genome mining databases and tools built expressly for AMP discovery. In light of the recent advancements, it is evident that targeted genome mining stands as a beacon of hope, offering immense potential to expedite the discovery of novel antimicrobials.

Methicillin-resistant Staphylococcus pseudintermedius: epidemiological changes, antibiotic resistance, and alternative therapeutic strategies

Staphylococcus pseudintermedius is a major opportunistic bacterial pathogen that belongs to the skin and mucosal microbiota of the dog. Since its global emergence around 2006, multidrug - methicillin-resistant S. pseudintermedius (MRSP) clones have become endemic worldwide. MRSP strains pose a significant threat to animal health and make antimicrobial therapy difficult due to their typical multidrug resistance phenotypes. The difficulty to treat MRSP infections using the current antimicrobials licensed for veterinary use has intensified research efforts to develop new treatment strategies and alternative anti-infective approaches to conventional antimicrobial therapy. The present narrative review outlines the latest changes in the epidemiology of MRSP with focus on the geographical distribution variability and antimicrobial resistance profiles in the main MRSP lineages. It also provides an overview of the effectiveness of currently available antimicrobials and the status of anti-infective alternatives to conventional antimicrobials.Recent studies have reported notable changes in the population structure of MRSP, with the emergence of new epidemic lineages, such as ST258, ST123, ST496, and ST551 in European countries and ST45, ST181, ST258, ST496 in non-European countries, which partly or totally replaced those that were initially prevalent, such as ST71 in Europe and ST68 in the US. Due to methicillin resistance often associated with the resistance to a broader number of antimicrobials, treating canine MRSP skin infection is challenging. Several alternative or supplementary treatment options to conventional antibiotics, especially for topical treatment, such as a novel water-soluble hydroxypyridinone-containing iron-chelating 9 kDa polymer (DIBI), antimicrobial peptides (AMPs), nanoparticles, and bacteriophages seem to be particularly interesting from a clinical perspective.

Acetylshikonin reduces the spread of antibiotic resistance via plasmid conjugation

The plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs) stands out as the primary driver behind the dissemination of antimicrobial resistance (AMR). Developing effective inhibitors that target conjugative transfer represents an potential strategy for addressing the issue of AMR. Here, we studied the effect of acetylshikonin (ASK), a botanical derivative, on plasmid conjugation. The conjugative transfer of RP4-7 plasmid inter and intra species was notably reduced by ASK. The conjugation process of IncI2 and IncX4 plasmids harbouring the mobile colistin resistance gene (mcr-1), IncX4 and IncX3 plasmids containing the carbapenem resistance gene (blaNDM-5), and IncFI and IncFII plasmids possessing the tetracycline resistance gene [tet(X4)] were also reduced by ASK. Importantly, the conjugative transfer frequency of mcr-1 positive IncI2 plasmid in mouse peritoneal conjugation model and gut conjugation model was reduced by ASK. The mechanism investigation showed that ASK disrupted the functionality of the bacterial cell membrane. Furthermore, the proton motive force (PMF) was dissipated. In addition, ASK blocked the electron transmission in bacteria's electron transport chain (ETC) through disturbing the quinone interaction, resulting in an insufficient energy supply for conjugation. Collectively, ASK is a potential conjugative transfer inhibitor, providing novel strategies to prevent the spread of AMR.

Phosphorylation as an Effective Tool to Improve Stability and Reduce Toxicity of Antimicrobial Peptides

Developing a straightforward and effective strategy to modify antimicrobial peptides (AMPs) is crucial in overcoming the challenges posed by their instability and toxicity. Phosphorylation can reduce toxicity and improve the stability of AMPs. Based on these, we designed a series of peptides and their corresponding phosphorylated forms. The results showed that all phosphorylated peptides displayed reduced toxicity and enhanced stability compared to their unphosphorylated counterparts. Among them, W3BipY8-P stood out as the most promising peptide, exhibiting similar antibacterial activity as its unphosphorylated analog W3BipY8 but with significantly reduced hemolytic activity (19-fold decrease), cytotoxicity (3.3-fold decrease), and an extended serum half-life 6.3 times longer than W3BipY8. W3BipY8-P exerted bactericidal effects by disrupting bacterial membranes. Notably, W3BipY8-P significantly prolonged the survival of bacteria-infected animals while its LD50 was 4.2 times higher than that of W3BipY8. These findings highlight phosphorylation as an effective strategy for improving the antimicrobial properties of AMPs.

Antimicrobial Peptides From the Gut Microbiome of the Centenarians: Diversification of Biosynthesis and Youthful Development of Resistance Genes

Antimicrobial peptides (AMPs) offer a potential solution to the antibiotic crisis owing to their antimicrobial properties, and the human gut biome may be a source of these peptides. However, the potential AMPs and AMP resistance genes (AMPRGs) of gut microbes in different age groups have not been thoroughly assessed. Here, we investigated the potential development of AMPs and the distribution pattern of AMPRGs in the gut microbiome at different ages by analyzing the intestinal metagenomic data of healthy individuals at different life stages (CG: centenarians group n = 20; OAG: older adults group: n = 15; YG: young group: n = 15). Age-related increases were observed in the potential AMPs within the gut microbiome, with centenarians showing a greater diversity of these peptides. However, the gut microbiome of the CG group had a lower level of AMPRGs compared to that of the OAG group, and it was similar to the level found in the YG group. Additionally, conventional probiotic strains showed a significant positive correlation with certain potential AMPs and were associated with a lower detection of resistance genes. Furthermore, comparing potential AMPs with existing libraries revealed limited similarity, indicating that current machine learning models can identify novel peptides in the gut microbiota. These results indicate that longevity may benefit from the diversity of AMPs and lower resistance genes. Our findings help explain the age advantage of the centenarians and identify the potential for antimicrobial peptide biosynthesis in the human gut microbiome, offering insights into the development of antimicrobial peptide resistance and the screening of probiotic strains.

Peptide Dimerization as a Strategy for the Development of Antileishmanial Compounds

Leishmaniasis is recognized as a serious public health problem in Brazil and around the world. The limited availability of drugs for treatment, added to the diversity of side effects and the emergence of resistant strains, shows the importance of research focused on the development of new molecules, thus contributing to treatments. Therefore, this work aimed to identify leishmanicidal compounds using a peptide dimerization strategy, as well as to understand their mechanisms of action. Herein, it was demonstrated that the dimerization of the peptide TSHa, (TSHa)2K, presented higher potency and selectivity than its monomeric form when evaluated against Leishmania mexicana and Leishmania amazonensis. Furthermore, these compounds are capable of inhibiting the parasite cysteine protease, an important target explored for the development of antileishmanial compounds, as well as to selectively interact with the parasite membranes, as demonstrated by flow cytometry, permeabilization, and fluorescence microscopy experiments. Based on this, the identified molecules are candidates for use in in vivo studies with animal models to combat leishmaniasis.

Membrane-Targeting Amphiphilic Honokiol Derivatives Containing an Oxazole Moiety as Potential Antibacterials against Methicillin-Resistant Staphylococcus aureus

Infections with methicillin-resistant Staphylococcus aureus (MRSA) are becoming increasingly serious, making the development of novel antimicrobials urgent. Here, we synthesized some amphiphilic honokiol derivatives bearing an oxazole moiety and investigated their antibacterial and hemolytic activities. Bioactivity evaluation showed that E17 possessed significant in vitro antibacterial activity against S. aureus and MRSA, along with low hemolytic activity. Moreover, E17 exhibited rapid bactericidal properties and was not susceptible to resistance. Mechanistic studies indicated that E17 interacts with phosphatidylglycerol and cardiolipin of bacterial cell membranes, leading to changes in cell membrane permeability and polarization, increased intracellular ROS, and leakage of DNA and proteins, thus accelerating bacterial death. Transcriptome analysis further demonstrated that E17 has membrane-targeting effects, affecting the expression of genes related to cell membranes and ABC transporter proteins. Notably, in vivo activity showed that E17 has prominent anti-MRSA efficacy, comparable to vancomycin, and is expected to be a new anti-MRSA drug candidate.

Mimics of Host Defense Peptides Derived from Dendronized Polylysines for Antibacterial and Anticancer Therapy

Bacteria in tumor microenvironments promote carcinogenesis and trigger complications, suggesting the significance of intervening in bacterial growth in cancer treatment. Here, dendrimer-derived mimics (DMs) of host defense peptides (HDPs) were designed for antibacterial and anticancer therapy, which feature a dendronized polylysine core and polycaprolactone arms. DMs displayed not only remarkable activities against Staphylococcus aureus and human lung cancer cells, but also exceptional selectivity. The membranolytic mechanism revealed by morphology analysis explained their low susceptibility to induce resistance. Further, the optimized DM inhibited tumor growth in the subcutaneous tumor model when administered via intraperitoneal injection and exhibited negligible toxicity to tissues. Overall, we combined the superiority of dendrimers and the mechanism from HDPs to design agents with dual antibacterial and anticancer activities that possess great potential for clinical oncology therapy.

Evaluation of the Antibacterial Potential of Two Short Linear Peptides YI12 and FK13 against Multidrug-Resistant Bacteria

The accelerating spread of antibiotic resistance has significantly weakened the clinical efficacy of existing antibiotics, posing a severe threat to public health. There is an urgent need to develop novel antimicrobial alternatives that can bypass the mechanisms of antibiotic resistance and effectively kill multidrug-resistant (MDR) pathogens. Antimicrobial peptides (AMPs) are one of the most promising candidates to treat MDR pathogenic infections since they display broad-spectrum antimicrobial activities and are less prone to achieve drug resistance. In this study, we investigated the antibacterial capability and mechanisms of two machine learning-driven linear peptide compounds termed YI12 and FK13. We reveal that YI12 and FK13 exhibit broad-spectrum antibacterial properties against clinically significant bacterial pathogens, inducing no or minimal hemolysis in mammalian red blood cells. We further ascertain that YI12 and FK13 are resilient to heat and acid-base conditions, and exhibit susceptibility to hydrolytic enzymes and divalent cations under physiological conditions. Initial mechanistic investigations reveal that YI12 and FK13 compromise bacterial membrane integrity, leading to membrane potential dissipation and excessive reactive oxygen species (ROS) generation. Collectively, our findings highlight the prospective utility of these two cationic amphiphilic peptides as broad-spectrum antibacterial agents.

Antimicrobial peptides: Opportunities and challenges in overcoming resistance

Antibiotic resistance represents a global health threat, challenging the efficacy of traditional antimicrobial agents and necessitating innovative approaches to combat infectious diseases. Among these alternatives, antimicrobial peptides have emerged as promising candidates against resistant pathogens. Unlike traditional antibiotics with only one target, these peptides can use different mechanisms to destroy bacteria, with low toxicity to mammalian cells compared to many conventional antibiotics. Antimicrobial peptides (AMPs) have encouraging antibacterial properties and are currently employed in the clinical treatment of pathogen infection, cancer, wound healing, cosmetics, or biotechnology. This review summarizes the mechanisms of antimicrobial peptides against bacteria, discusses the mechanisms of drug resistance, the limitations and challenges of AMPs in peptide drug applications for combating drug-resistant bacterial infections, and strategies to enhance their capabilities.

Mystery of the Passerini Reaction for the Synthesis of the Antimicrobial Peptidomimetics against Nosocomial Pathogenic Bacteria

The first example of applying salicylaldehyde derivatives, as well as coumarin with the formyl group at the C8 position in its structure, as carbonyl partners in a three-component Passerini reaction, is presented. As a result of research on the conditions of the Passerini reaction, the important role of the hydroxyl group in the salicylaldehyde used in the course of the multicomponent reaction was revealed. When an aldehyde with an unprotected hydroxyl group is used, only two-component α-hydroxy amide products are obtained. In contrast, the use of acylated aldehyde results in three-component α-acyloxy amide products with high efficiency. The developed protocol gives access to structurally diversified peptidomimetics with good yield. The compounds were also evaluated as antimicrobial agents against selected strains of nosocomial pathogenic bacteria. The structure-activity relationship revealed that inhibitory activity is strongly related to the presence of the trifluoromethyl group (CF3) or the methyl group at the C4 position in an unsaturated lactone ring of the coumarin scaffold. MIC and MBC studies were carried out on eight selected pathogenic bacteria strains (Gram-positive pathogenic Staphylococcus aureus strain (ATCC 23235), as well as on Gram-negative E. coli (K12 (ATCC 25404), R2 (ATCC 39544), R3 (ATCC 11775), and R4 (ATCC 39543)), Acinetobacter baumannii (ATCC 17978), Pseudomonas aeruginosa (ATCC 15442), and Enterobacter cloacae (ATCC 49141) have shown that the tested compounds show a strong bactericidal effect at low concentrations. Among all agents investigated, five exhibit higher antimicrobial activity than those observed for commonly used antibiotics. It should be noted that all the compounds tested showed very high activity against S. aureus, which is the main source of nosocomial infections that cause numerous fatalities. Additionally, the cytotoxicity of sixteen derivatives was measured with the use of the MTT test on BALB/c3T3 mouse fibroblast cell lines. The cytotoxicity studies revealed that the tested substances exert a similar or lower effect on cell proliferation than that observed for commonly used antibiotics within the range of therapeutic doses. A parallel MTT assay using ciprofloxacin, bleomycin, and cloxacillin showed that these antibiotics are more cytotoxic when tested in mammalian cells, and cell viability is in the range of 85.0-89.9%. Furthermore, we have shown that the studied coumarin-based peptidomimetics, depending on their structural characteristics, are nonselective and act efficiently against various Gram-positive and Gram-negative pathogens, which is of great importance for hospitalised patients.

Antimicrobial peptides as promising antibiotic adjuvants to combat drug-resistant pathogens

The widespread antimicrobial resistance (AMR) calls for the development of new antimicrobial strategies. Antibiotic adjuvant rescues antibiotic activity and increases the life span of the antibiotics, representing a more productive, timely, and cost-effective strategy in fighting drug-resistant pathogens. Antimicrobial peptides (AMPs) from synthetic and natural sources are considered new-generation antibacterial agents. Besides their direct antimicrobial activity, growing evidence shows that some AMPs effectively enhance the activity of conventional antibiotics. The combinations of AMPs and antibiotics display an improved therapeutic effect on antibiotic-resistant bacterial infections and minimize the emergence of resistance. In this review, we discuss the value of AMPs in the age of resistance, including modes of action, limiting evolutionary resistance, and their designing strategies. We summarise the recent advances in combining AMPs and antibiotics against antibiotic-resistant pathogens, as well as their synergistic mechanisms. Lastly, we highlight the challenges and opportunities associated with the use of AMPs as potential antibiotic adjuvants. This will shed new light on the deployment of synergistic combinations to address the AMR crisis.

Antimicrobial Peptides towards Clinical Application-A Long History to Be Concluded

Antimicrobial peptides (AMPs) are molecules with an amphipathic structure that enables them to interact with bacterial membranes. This interaction can lead to membrane crossing and disruption with pore formation, culminating in cell death. They are produced naturally in various organisms, including humans, animals, plants and microorganisms. In higher animals, they are part of the innate immune system, where they counteract infection by bacteria, fungi, viruses and parasites. AMPs can also be designed de novo by bioinformatic approaches or selected from combinatorial libraries, and then produced by chemical or recombinant procedures. Since their discovery, AMPs have aroused interest as potential antibiotics, although few have reached the market due to stability limits or toxicity. Here, we describe the development phase and a number of clinical trials of antimicrobial peptides. We also provide an update on AMPs in the pharmaceutical industry and an overall view of their therapeutic market. Modifications to peptide structures to improve stability in vivo and bioavailability are also described.

Oral Administration of Antimicrobial Peptide NZ2114 Through the Microalgal Bait Tetraselmis subcordiformis (Wille) Butcher for Improving the Immunity and Gut Health in Turbot (Scophthalmus maximus L.)

Antibiotics are widely used in aquaculture to treat the bacterial diseases. However, the improper use of antibiotics could lead to environmental pollution and development of resistance. As a safe and eco-friendly alternative, antimicrobial peptides (AMPs) are commonly explored as therapeutic agents. In this study, a mutant strain of Tetraselmis subcordiformis containing AMP NZ2114 was developed and used as an oral drug delivery system to reduce the use of antibiotics in turbot (Scophthalmus maximus) aquaculture. The gut, kidney, and liver immune-related genes and their effects on gut digestion and bacterial communities in turbot fed with NZ2114 were evaluated in an 11-day feeding experiment. The results showed that compared with the group fed with wild-type T. subcordiformis, the group fed with T. subcordiformis transformants containing NZ2114 was revealed with decreased levels of both pro-inflammatory factors (TNF-α and IL-1β), inhibitory effect on Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio splendidus demonstrated by the in vitro simulation experiments, and increased richness and diversity of the gut microbiota of turbot. In conclusion, our study provided a novel, beneficial, and low-cost method for controlling bacteria in turbot culture through the oral drug delivery systems.

Evaluation of the synergistic potential and mechanisms of action for de novo designed cationic antimicrobial peptides

Antimicrobial peptides (AMPs) have emerged as promising candidates in combating antimicrobial resistance - a growing issue in healthcare. However, to develop AMPs into effective therapeutics, a thorough analysis and extensive investigations are essential. In this study, we employed an in silico approach to design cationic AMPs de novo, followed by their experimental testing. The antibacterial potential of de novo designed cationic AMPs, along with their synergistic properties in combination with conventional antibiotics was examined. Furthermore, the effects of bacterial inoculum density and metabolic state on the antibacterial activity of AMPs were evaluated. Finally, the impact of several potent AMPs on E. coli cell envelope and genomic DNA integrity was determined. Collectively, this comprehensive analysis provides insights into the unique characteristics of cationic AMPs.

Development of Antibacterial Peptides with Membrane Disruption and Folate Pathway Inhibitory Activities against Methicillin-Resistant Staphylococcus aureus

Antimicrobial peptides (AMPs) offer an opportunity to overcome multidrug resistance. Here, novel peptides were designed based on AMP fragments derived from sea cucumber hemolytic lectin to enhance anti-methicillin-resistant Staphylococcus aureus (MRSA) activity with less side effects. Two designed peptides, CGS19 (LARVARRVIRFIRRAW-NH2) and CGS20 (RRRLARRLIFFIRRAW-NH2), exhibited strong antibacterial activities against clinically isolated MRSA with MICs of 3-6 μM, but no obvious cytotoxicity was observed. Consistently, CGS19 and CGS20 exerted rapid bactericidal activity and effectively induced 5.9 and 5.8 log reduction of MRSA counts in mouse subeschar, respectively. Further, CGS19 and CGS20 kill bacteria not only through disturbing membrane integrity but also by binding formate-tetrahydrofolate ligase, a key enzyme in the folate metabolism pathway, thereby inhibiting the folate pathway of MRSA. CGS19 and CGS20 are promising lead candidates for drug development against MRSA infection. The dual mechanisms on the identical peptide sequence or scaffold might be an underappreciated manner of treating life-threatening pathogens.

Silver(I) complexes with amino acid and dipeptide ligands - Chemical and antimicrobial relevant comparison (mini review)

Diseases caused by various microorganisms accompany humans (as well as animals) throughout their whole lives. After germs penetration to the body, the incubation period and infection developing, an infection can cause mild or severe symptoms, not infrequently even death. The immune system naturally defends itself against pathogens with various mechanisms. One of them is the synthesis of antimicrobial peptides. In the case of serious and severe infections, it is currently possible to help the natural immunity by administration of antimicrobial drugs (AMB) with good success since their discovery at the beginning of the last century. However, their excessive use leads to the development of pathogenic microorganisms' resistance to AMB drugs. Based on this, it is necessary to constantly develop new classes of AMB drugs that will be effective against pathogens, even resistant ones. The field of bioinorganic chemistry, similarly to other biological, chemical, or pharmaceutical sciences, discovers various options and approaches for antimicrobial treatment, from the development of new drugs to drug delivery systems. One of the approaches is the design and preparation of potential drugs based on metal ions and antimicrobial peptides. Various metal ions and amino acid or peptide ligands are used for this purpose. In this mini review, we focused on a reliable comparison of the chemical structure and biological properties of selected silver(I) complexes based on amino acids and dipeptides.

Design of phenothiazine-based cationic amphiphilic derivatives incorporating arginine residues: Potential membrane-active broad-spectrum antimicrobials combating pathogenic bacteria in vitro and in vivo

Multidrug-resistant bacteria infections pose an increasingly serious threat to human health, and the development of antimicrobials is far from meeting the clinical demand. It is urgent to discover and develop novel antibiotics to combat bacterial resistance. Currently, the development of membrane active antimicrobial agents is an attractive strategy to cope with antimicrobial resistance issues. In this study, the synthesis and biological evaluation of cationic amphiphilic phenothiazine-based derivatives were reported. Among them, the most promising compound 30 bearing a n-heptyl group and two arginine residues displayed potent bactericidal activity against both Gram-positive (MICs = 1.56 μg/mL) and Gram-negative bacteria (MICs = 3.125-6.25 μg/mL). Compound 30 showed low hemolysis activity (HC50 = 281.4 ± 1.6 μg/mL) and low cytotoxicity (CC50 ＞ 50 μg/mL) toward mammalian cells, as well as excellent salt resistance. Compound 30 rapidly killed bacteria by acting on the bacterial cell membrane and appeared less prone to resistance. Importantly, compound 30 showed potent in vivo efficacy in a murine model of bacterial keratitis. Hence, the results suggested compound 30 has a promising prospect as a broad-spectrum antibacterial agent for the treatment of drug-resistant bacterial infections.

Antimicrobial Peptidomimetics Prevent the Development of Resistance against Gentamicin and Ciprofloxacin in Staphylococcus and Pseudomonas Bacteria

Bacteria readily acquire resistance to traditional antibiotics, resulting in pan-resistant strains with no available treatment. Antimicrobial resistance is a global challenge and without the development of effective antimicrobials, the foundation of modern medicine is at risk. Combination therapies such as antibiotic-antibiotic and antibiotic-adjuvant combinations are strategies used to combat antibiotic resistance. Current research focuses on antimicrobial peptidomimetics as adjuvant compounds, due to their promising activity against antibiotic-resistant bacteria. Here, for the first time we demonstrate that antibiotic-peptidomimetic combinations mitigate the development of antibiotic resistance in Staphylococcus aureus and Pseudomonas aeruginosa. When ciprofloxacin and gentamicin were passaged individually at sub-inhibitory concentrations for 10 days, the minimum inhibitory concentrations (MICs) increased up to 32-fold and 128-fold for S. aureus and P. aeruginosa, respectively. In contrast, when antibiotics were passaged in combination with peptidomimetics (Melimine, Mel4, RK758), the MICs of both antibiotics and peptidomimetics remained constant, indicating these combinations were able to mitigate the development of antibiotic-resistance. Furthermore, antibiotic-peptidomimetic combinations demonstrated synergistic activity against both Gram-positive and Gram-negative bacteria, reducing the concentration needed for bactericidal activity. This has significant potential clinical applications-including preventing the spread of antibiotic-resistant strains in hospitals and communities, reviving ineffective antibiotics, and lowering the toxicity of antimicrobial chemotherapy.

Visualizing the membrane disruption action of antimicrobial peptides by cryo-electron tomography

The abuse of antibiotics has led to the emergence of multidrug-resistant microbial pathogens, presenting a pressing challenge in global healthcare. Membrane-disrupting antimicrobial peptides (AMPs) combat so-called superbugs via mechanisms different than conventional antibiotics and have good application prospects in medicine, agriculture, and the food industry. However, the mechanism-of-action of AMPs has not been fully characterized at the cellular level due to a lack of high-resolution imaging technologies that can capture cellular-membrane disruption events in the hydrated state. Previously, we reported PepD2M, a de novo-designed AMP with potent and wide-spectrum bactericidal and fungicidal activity. In this study, we use cryo-electron tomography (cryo-ET) and high-speed atomic force microscopy (HS-AFM) to directly visualize the pepD2M-induced disruption of the outer and inner membranes of the Gram-negative bacterium Escherichia coli, and compared with a well-known pore-forming peptide, melittin. Our high-resolution cryo-ET images reveal how pepD2M disrupts the E. coli membrane using a carpet/detergent-like mechanism. Our studies reveal the direct membrane-disrupting consequence of AMPs on the bacterial membrane by cryo-ET, and this information provides critical insights into the mechanisms of this class of antimicrobial agents.

In Vivo Efficacy and Toxicity of an Antimicrobial Peptide in a Model of Endotoxin-Induced Pulmonary Inflammation

SET-M33 is a synthetic peptide that is being developed as a new antibiotic against major Gram-negative bacteria. Here we report two in vivo studies to assess the toxicity and efficacy of the peptide in a murine model of pulmonary inflammation. First, we present the toxicity study in which SET-M33 was administered to CD-1 mice by snout inhalation exposure for 1 h/day for 7 days at doses of 5 and 20 mg/kg/day. The results showed adverse clinical signs and effects on body weight at the higher dose, as well as some treatment-related histopathology findings (lungs and bronchi, nose/turbinates, larynx and tracheal bifurcation). On this basis, the no observable adverse effect level (NOAEL) was considered to be 5 mg/kg/day. We then report an efficacy study of the peptide in an endotoxin (LPS)-induced pulmonary inflammation model. Intratracheal administration of SET-M33 at 0.5, 2 and 5 mg/kg significantly inhibited BAL neutrophil cell counts after an LPS challenge. A significant reduction in pro-inflammatory cytokines, KC, MIP-1α, IP-10, MCP-1 and TNF-α was also recorded after SET-M33 administration.

The efficacy of anti-proteolytic peptide R7I in intestinal inflammation, function, microbiota, and metabolites by multi-omics analysis in murine bacterial enteritis

Increased antibiotic resistance poses a major limitation in tackling inflammatory bowel disease and presents a large challenge for global health care. Antimicrobial peptides (AMPs) are a potential class of antimicrobial agents. Here, we have designed the potential oral route for antimicrobial peptide R7I with anti-proteolytic properties to deal with bacterial enteritis in mice. The results revealed that R7I protected the liver and gut from damage caused by inflammation. RNA-Seq analysis indicated that R7I promoted digestion and absorption in the small intestine by upregulating transmembrane transporter activity, lipid and small molecule metabolic processes and other pathways, in addition to upregulating hepatic steroid biosynthesis and fatty acid degradation. For the gut microbiota, Clostridia were significantly reduced in the R7I-treated group, and Odoribacteraceae, an efficient isoalloLCA-synthesizing strain, was the main dominant strain, protecting the gut from potential pathogens. In addition, we further discovered that R7I reduced the accumulation of negative organic acid metabolites. Overall, R7I exerted better therapeutic and immunomodulatory potential in the bacterial enteritis model, greatly reduced the risk of disease onset, and provided a reference for the in vivo application of antimicrobial peptides.

Discovery and Mechanism of Action of a Novel Antimicrobial Peptide from an Earthworm

The robust innate immune system of the earthworm provides a potential source of natural antimicrobial peptides (AMPs). However, the cost and high rediscovery rate of direct separation and purification limits their discovery. Genome sequencing of numerous earthworm species facilitates the discovery of new antimicrobial peptides. Through predicting potential antimicrobial peptides in the open reading frames of the Eisenia andrei genome and sequence optimization, a novel antimicrobial peptide, named EWAMP-R (RIWWSGGWRRWRW), was identified. EWAMP-R demonstrated good activity against various bacteria, including drug-resistant strains. The antibacterial mechanisms of EWAMP-R were explored through molecular simulation and wet-laboratory experiments. These experiments demonstrated that the bacterial membrane may be one of the targets of EWAMP-R but that there may be different interactions with Gram-negative and Gram-positive bacterial membranes. EWAMP-R can disrupt bacterial membrane integrity; however, at low concentrations, it appears that EWAMP-R may get through the membrane of Escherichia coli instead of damaging it directly, implying the existence of a secondary response. Gene expression studies identified that in E. coli, only the apoptosis-like cell death (ALD) pathway was activated, while in Staphylococcus aureus, the MazEF pathway was also upregulated, limiting the influence of the ALD pathway. The different antimicrobial actions against Gram-positive and -negative bacteria can provide important information on the structure-activity relationship of AMPs and facilitate AMP design with higher specificity. This study identified a new source of antibacterial agents that has the potential to address the increasingly serious issue of antibiotic resistance. IMPORTANCE Drug-resistant bacteria are a great threat to public health and drive the search for new antibacterial agents. The living environment of earthworms necessitates a strong immune system, and therefore, they are potentially a rich resource of novel antibiotics. A novel AMP, EWAMP-R, with high antibacterial activity was found through in silico analysis of the Eisenia andrei genome. Molecular analysis investigating the interactions between EWAMP-R and the cell membrane demonstrated the importance of tryptophan and arginine residues to EWAMP-R activity. Additionally, the different secondary responses found between E. coli and S. aureus were in accordance with a common phenomenon where some antibacterial agents only target specific species of bacteria. These results provided useful molecular information to support further AMP research and design. Our study expands the sources of antimicrobial peptides and also helps to explain the adaptability of earthworms to their environment.

Effects of Dimerization, Dendrimerization, and Chirality in p-BthTX-I Peptide Analogs on the Antibacterial Activity and Enzymatic Inhibition of the SARS-CoV-2 PLpro Protein

Recent studies have shown that the peptide [des-Cys¹¹,Lys¹²,Lys¹³-(p-BthTX-I)₂K] (p-Bth) is a p-BthTX-I analog that shows enhanced antimicrobial activity, stability and hemolytic activity, and is easy to obtain compared to the wild-type sequence. This molecule also inhibits SARS-CoV-2 viral infection in Vero cells, acting on SARS-CoV-2 PL^pro enzymatic activity. Thus, the present study aimed to assess the effects of structural modifications to p-Bth, such as dimerization, dendrimerization and chirality, on the antibacterial activity and inhibitory properties of PL^pro. The results showed that the dimerization or dendrimerization of p-Bth was essential for antibacterial activity, as the monomeric structure led to a total loss of, or significant reduction in, bacterial activities. The dimers and tetramers obtained using branched lysine proved to be prominent compounds with antibacterial activity against Gram-positive and Gram-negative bacteria. In addition, hemolysis rates were below 10% at the corresponding concentrations. Conversely, the inhibitory activity of the PL^pro of SARS-CoV-2 was similar in the monomeric, dimeric and tetrameric forms of p-Bth. Our findings indicate the importance of the dimerization and dendrimerization of this important class of antimicrobial peptides, which shows great potential for antimicrobial and antiviral drug-discovery campaigns.

Members of the histone-derived antimicrobial peptide family from the pearl oyster Pinctada fucata martensii: Inhibition of bacterial growth

Because it is difficult to isolate standard antimicrobial peptides (AMPs) using traditional biochemical approaches, we designed, synthesized, and evaluated a series of structurally altered histone-derived AMPs (HDAPs) from the pearl oyster Pinctada fucata martensii using molecular cloning approaches. Four histone-homolog genes (PmH2A, PmH2B, PmH3, and PmH4-1) were identified, of which PmH2A and PmH2B had yet to be described. PmH2A and PmH2B were therefore cloned using Rapid Amplification of cDNA Ends (RACE) and characterized. Constitutive PmH2A and PmH2B mRNA expression was detected in all six pearl oyster tissues tested, with comparatively greater transcript abundance in the gonads. Because α-helical content, hydrophilicity index, and the presence of a proline hinge may be the three important factors influencing the antimicrobial efficacy of HDAPs, we synthesized a series of eight N- and C-terminally truncated or amino acid-substituted synthetic candidate HDAP analogs derived from PmH2A, PmH2B, PmH3, and PmH4-1. Only the PmH2A- and PmH4-derived AMPs inhibited bacterial growth. The PmH2A-derived AMPs were α-helical proteins, while the PmH4-derived AMPs were extended strand/random coil proteins. Our results suggested that having an α-helical structure was particularly important for the antibacterial efficacy of the PmH2A-derived peptides; amphipathic structures (hydrophilic index, 0.3 to -0.3) may enhance the antimicrobial function of both the PmH2A- and PmH4-derived peptides. The high antibacterial efficacy of one of the HDAP analogs studied, PmH2A-AMP (5-13) [KLLK]₃, indicated that this protein may represent a promising candidate for the treatment of bacterial infections in aquaculture mollusk species. This first study of HDAPs from the pearl oyster P. f. martensii provides new insights into the design and function of highly effective antimicrobial peptides.

Safety evaluations of a synthetic antimicrobial peptide administered intravenously in rats and dogs

The antimicrobial peptide SET-M33 is under study for the development of a new antibiotic against major Gram-negative pathogens. Here we report the toxicological evaluation of SET-M33 administered intravenously to rats and dogs. Dose range finding experiments determined the doses to use in toxicokinetic evaluation, clinical biochemistry analysis, necroscopy and in neurological and respiratory measurements. Clinical laboratory investigations in dogs and rats showed a dose-related increase in creatinine and urea levels, indicating that the kidneys are the target organ. This was also confirmed by necroscopy studies of animal tissues, where signs of degeneration and regeneration were found in kidney when SET-M33 was administered at the highest doses in the two animal species. Neurological toxicity measurements by the Irwin method and respiratory function evaluation in rats did not reveal any toxic effect even at the highest dose. Finally, repeated administration of SET-M33 by short infusion in dogs revealed a no-observed-adverse-effect-level of 0.5 mg/kg/day.

10-mer and 9-mer WALK Peptides with Both Antibacterial and Anti-Inflammatory Activities

Natural antimicrobial peptides (AMPs) are multifunctional host defense peptides (HDPs) that are valuable for various therapeutic applications. In particular, natural and artificial AMPs with dual antibacterial immunomodulatory functions emerged as promising candidates for the development of therapeutic agents to treat infectious inflammation. In an effort to develop useful AMP variants with short lengths and simple amino acid composition, we devised a de novo design strategy to generate a series of model peptide isomer sequences, named WALK peptides, i.e., tryptophan (W)-containing amphipathic-helical (A) leucine (L)/lysine (K) peptides. Here, we generated two groups of WALK peptide isomers: W₂L₄K₄ (WALK244.01~WALK244.10) and W₂L₄K₃ (WALK243.01~WALK243.09). Most showed apparent antibacterial activities against both Gram-positive and Gram-negative bacteria at a concentration of approximately 4 μg/mL along with varied hemolytic activities against human red blood cells. In addition, some exhibited significant anti-inflammatory activities without any significant cytotoxicity in macrophages. Collectively, these results suggest that the two selected peptides, WALK244.04 and WALK243.04, showed promise for the development of antibacterial and anti-inflammatory agents.

Anti-Virulence Potential of a Chionodracine-Derived Peptide against Multidrug-Resistant Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is an opportunistic pathogen causing several chronic infections resistant to currently available antibiotics. Its pathogenicity is related to the production of different virulence factors such as biofilm and protease secretion. Pseudomonas communities can persist in biofilms that protect bacterial cells from antibiotics. Hence, there is a need for innovative approaches that are able to counteract these virulence factors, which play a pivotal role, especially in chronic infections. In this context, antimicrobial peptides are emerging drugs showing a broad spectrum of antibacterial activity. Here, we tested the anti-virulence activity of a chionodracine-derived peptide (KHS-Cnd) on five P. aeruginosa clinical isolates from cystic fibrosis patients. We demonstrated that KHS-Cnd impaired biofilm development and caused biofilm disaggregation without affecting bacterial viability in nearly all of the tested strains. Ultrastructural morphological analysis showed that the effect of KHS-Cnd on biofilm could be related to a different compactness of the matrix. KHS-Cnd was also able to reduce adhesion to pulmonary cell lines and to impair the invasion of host cells by P. aeruginosa. A cytotoxic effect of KHS-Cnd was observed only at the highest tested concentration. This study highlights the potential of KHS-Cnd as an anti-biofilm and anti-virulence molecule against P. aeruginosa clinical strains.

Antimicrobial peptides: Sustainable application informed by evolutionary constraints

The proliferation and global expansion of multidrug-resistant (MDR) bacteria have deepened the need to develop novel antimicrobials. Antimicrobial peptides (AMPs) are regarded as promising antibacterial agents because of their broad-spectrum antibacterial activity and multifaceted mechanisms of action with non-specific targets. However, if AMPs are to be applied sustainably, knowledge of how they induce resistance in pathogenic bacteria must be mastered to avoid repeating the traditional antibiotic resistance mistakes currently faced. Furthermore, the evolutionary constraints on the acquisition of AMP resistance by microorganisms in the natural environment, such as functional compatibility and fitness trade-offs, inform the translational application of AMPs. Consequently, the shortcut to achieve sustainable utilization of AMPs is to uncover the evolutionary constraints of bacteria on AMP resistance in nature and find the tricks to exploit these constraints, such as applying AMP cocktails to minimize the efficacy of selection for resistance or combining nanomaterials to maximize the costs of AMP resistance. Altogether, this review dissects the benefits, challenges, and opportunities of utilizing AMPs against disease-causing bacteria, and highlights the use of AMP cocktails or nanomaterials to proactively address potential AMP resistance crises in the future.

Engineering Approaches for the Development of Antimicrobial Peptide-Based Antibiotics

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

The antimicrobial peptide LI14 combats multidrug-resistant bacterial infections

The prevalence of multidrug-resistant (MDR) pathogens raises public fears of untreatable infections and represents a huge health risk. There is an urgent need to exploit novel antimicrobial agents. Due to the unique mechanisms, antimicrobial peptides (AMPs) with a low probability to achieve resistance are regarded as potential antibiotic alternatives to address this issue. Herein, we develop a panel of synthetic peptide compounds with novel structures based on the database filters technology (DFT), and the lead peptide LI14 shows potent antibacterial activity against all tested drug-resistant bacteria. LI14 exhibits rapid bactericidal activity and excellent anti-biofilm and -persisters activity, simultaneously showing a low propensity to induce resistance. Moreover, LI14 shows tolerance against pH, temperatures, and pepsin treatment, and no detectable toxicity both in vitro and in vivo. Mechanistic studies revealed that LI14 induces membrane damage by targeting bacterial-specific membrane components and dissipates the proton motive force (PMF), thereby resulting in metabolic perturbations and the accumulation of toxic metabolic products. Furthermore, LI14 sensitizes clinically relevant antibiotics against MDR bacteria. In animal models of infection, LI14 or combined with antibiotics are effective against drug-resistant pathogens. These findings suggest that LI14 is a promising antibiotic candidate to tackle MDR bacterial infections.

A synthetic peptide LI14 demonstrates potent antibacterial activity against drug-resistant bacteria in vitro and in vivo by inducing membrane damage and disrupting membrane potential leading to metabolic perturbation.

Florfenicol-Polyarginine Conjugates Exhibit Promising Antibacterial Activity Against Resistant Strains

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

Pharmacokinetics and Pharmacodynamics of Fungal Defensin NZX Against Staphylococcus aureus-Induced Mouse Peritonitis Model

Staphylococcus aureus (S. aureus) is one of the most common pathogenic bacteria responsible for causing a life-threatening peritonitis disease. NZX, as a variant of fungal defensin plectasin, displayed potent antibacterial activity against S. aureus. In this study, the antibacterial and resistance characteristics, pharmacokinetics, and pharmacodynamics of NZX against the S. aureus E48 and S. aureus E48-induced mouse peritonitis model were studied, respectively. NZX exhibited a more rapid killing activity to S. aureus (minimal inhibitory concentration, 1 μg/ml) compared with linezolid, ampicillin and daptomycin, and serial passaging of S. aureus E48 for 30 days at 1/2 × MIC, NZX had a lower risk of resistance compared with ampicillin and daptomycin. Also, it displayed a high biocompatibility and tolerance to physiological salt, serum environment, and phagolysosome proteinase environment, except for acid environment in phagolysosome. The murine serum protein-binding rate of NZX was 89.25% measured by ultrafiltration method. Based on the free NZX concentration in serum after tail vein administration, the main pharmacokinetic parameters for T_1/2, C_max, V_d, MRT, and AUC ranged from 0.32 to 0.45 h, 2.85 to 20.55 μg/ml, 1469.10 to 2073.90 ml/kg, 0.32 to 0.56 h, and 1.11 to 8.89 μg.h/ml, respectively. Additionally, the in vivo pharmacodynamics against S. aureus demonstrated that NZX administrated two times by tail vein at 20 mg/kg could rescue all infected mice in the lethal mouse peritonitis model. And NZX treatment (20 mg/kg) significantly reduced CFU counts in the liver, lung, and spleen, especially for intracellular bacteria in the peritoneal fluid, which were similar or superior to those of daptomycin. In vivo efficacies of NZX against total bacteria and intracellular bacteria were significantly correlated with three PK/PD indices of ƒAUC/MIC, ƒC_max/MIC, and ƒT% > MIC analyzed by a sigmoid maximum-effect model. These results showed that NZX may be a potential candidate for treating peritonitis disease caused by intracellular S. aureus.

In vitro and in silico evaluation of antimicrobial properties of Delphinium cashmerianum L., a medicinal herb growing in Kashmir, India

ETHNOPHARMACOLOGICAL RELEVANCE

Microorganisms are developing resistance to synthetic drugs. As a result, the search for novel antimicrobial compounds has become an urgent need. Medicinal plants are commonly used as traditional medicine and Delphinium is one of the prominent genus used in the treatment of several diseases.

AIM OF THE STUDY

The present study aimed to determine the in vitro and in silico antimicrobial activities of petroleum ether, ethyl acetate and methanol extracts from the leaf samples of plant (Delphinium cashmerianum L.) against various bacterial and fungal strains.

MATERIAL AND METHODS

Three extracts of Delphinium cashmerianum prepared and 88 bioactive compounds were analyzed through LC-MS data with the vast majority of them having therapeutic applications. These extracts have been screened for the antimicrobial activity against various bacterial (Escherichia coli, Micrococcus luteus, Klebsiella pneumoniae, Streptococcus pneumonia, Haemophilus influenzae, Neisseria mucosa) and fungal (Candida albicans, Candida glabrata, Candida paropsilosis) species through in silico molecular docking approach using autodock vina software, molecular dynamic simulation (MDS), in vitro disc diffusion and broth microdilution method for minimum inhibitory concentration (MIC) evaluation.

RESULTS

Our results demonstrated that all three extracts were active against the whole set of microorganisms. The ethyl acetate extract was the most active against S.pneumonia, K. pneumoniae and C. albicans with a minimum inhibitory concentration (MIC) value of 6.25, 25 and 50 μg/ml, respectively. The petroleum ether and methanol extracts were active against S.pneumonia and N.mucosa with MIC values of 25 and 50 μg/ml. Furthermore, we also performed the in silico virtual screening of all these compounds obtained from LC-MS data analysis against various known drug targets of bacterium and fungi. Upon analysis, we obtained 5 compounds that were efficiently binding to the drug targets. However, after performing exhaustive molecular docking and molecular dynamic simulation (MDS) analysis, it was observed that Daidzein compound is bound to drug targets more efficiently.

CONCLUSION

The results showed that these plant extracts exhibit antimicrobial activity and ethyl acetate extract proved to exhibit the most effective antibacterial and antifungal properties.

Peptide Conjugates Derived from flg15, Pep13, and PIP1 That Are Active against Plant-Pathogenic Bacteria and Trigger Plant Defense Responses

Thirty peptide conjugates were designed by combining an antimicrobial peptide (BP16, BP100, BP143, KSL-W, BP387, or BP475) at the N- or C-terminus of a plant defense elicitor peptide (flg15, BP13, Pep13, or PIP1). These conjugates were highly active in vitro against six plant-pathogenic bacteria, especially against Xanthomonas arboricola pv. pruni, Xanthomonas fragariae and Xanthomonas axonopodis pv. vesicatoria. The most active peptides were those incorporating Pep13. The order of the conjugation influenced the antibacterial activity and the hemolysis. Regarding the former, peptide conjugates incorporating the elicitor peptide flg15 or Pep13 at the C-terminus were, in general, more active against Pseudomonas syringae pv. actinidiae and P. syringae pv. syringae, whereas those bearing these elicitor peptides at the N-terminus displayed higher activity against Erwinia. amylovora and the Xanthomonas species. The best peptide conjugates displayed MIC values between 0.8 and 12.5 μM against all the bacteria tested and also had low levels of hemolysis and low phytotoxicity. Analysis of the structural and physicochemical parameters revealed that a positive charge ranging from +5 to +7 and a moderate hydrophobic moment/amphipathic character is required for an optimal biological profile. Interestingly, flg15-BP475 exhibited a dual activity, causing the upregulation of the same genes as flg15 and reducing the severity of bacterial spot in tomato plants with a similar or even higher efficacy than copper oxychloride. Characterization by nuclear magnetic resonance (NMR) of the secondary structure of flg15-BP475 showed that residues 10 to 25 fold into an α-helix. This study establishes trends to design new bifunctional peptides useful against plant diseases caused by plant-pathogenic bacteria.

IMPORTANCE The consequences of plant pathogens on crop production together with the lack of effective and environmentally friendly pesticides evidence the need of new agents to control plant diseases. Antimicrobial and plant defense elicitor peptides have emerged as good candidates to tackle this problem. This study focused on combining these two types of peptides into a single conjugate with the aim to potentiate the activity of the individual fragments. Differences in the biological activity of the resulting peptide conjugates were obtained depending on their charge, amphipathicity, and hydrophobicity, as well as on the order of the conjugation of the monomers. This work provided bifunctional peptide conjugates able to inhibit several plant-pathogenic bacteria, to stimulate plant defense responses, and to reduce the severity of bacterial spot in tomato plants. Thus, this study could serve as the basis for the development of new antibacterial/plant defense elicitor peptides to control bacterial plant pathogens.

Heterochiral β-Peptide Polymers Combating Multidrug-Resistant Cancers Effectively without Inducing Drug Resistance

Multidrug resistance to chemotherapeutic drugs is one of the major causes for the failure of cancer treatment. Therefore, there is an urgent need to develop anticancer agents that can combat multidrug-resistant cancers effectively and mitigate drug resistance. Here, we report a rational design of anticancer heterochiral β-peptide polymers as synthetic mimics of host defense peptides to combat multidrug-resistant cancers. The optimal polymer shows potent and broad-spectrum anticancer activities against multidrug-resistant cancer cells and is insusceptible to anticancer drug resistance owing to its membrane-damaging mechanism. The in vivo study indicates that the optimal polymer efficiently inhibits the growth and distant transfer of solid tumors and the metastasis and seeding of circulating tumor cells. Moreover, the polymer shows excellent biocompatibility during anticancer treatment on animals. In addition, the β-peptide polymers address those prominent shortcomings of anticancer peptides and have superior stability against proteolysis, easy synthesis in large scale, and low cost. Collectively, the structural diversity and superior anticancer performance of β-peptide polymers imply an effective strategy in designing and finding anticancer agents to combat multidrug-resistant cancers effectively while mitigating drug resistance.

Biological Functions and Applications of Antimicrobial Peptides

Abstract:

Despite antimicrobial resistance, which is attributed to the misuse of broad-spectrum antibiotics, antibiotics can indiscriminately kill pathogenic and beneficial microorganisms. These events disrupt the delicate microbial balance in both humans and animals, leading to secondary infections and other negative effects. Antimicrobial peptides (AMPs) are functional natural biopolymers in plants and animals. Due to their excellent antimicrobial activities and absence of microbial resistance, AMPs have attracted enormous research attention. We reviewed the antibacterial, antifungal, antiviral, antiparasitic, as well as antitumor properties of AMPs and research progress on AMPs. In addition, we highlighted various recommendations and potential research areas for their progress and challenges in practical applications.

Secondary Amine Pendant β-Peptide Polymers Displaying Potent Antibacterial Activity and Promising Therapeutic Potential in Treating MRSA-Induced Wound Infections and Keratitis

Interest in developing antibacterial polymers as synthetic mimics of host defense peptides (HPDs) has accelerated in recent years to combat antibiotic-resistant bacterial infections. Positively charged moieties are critical in defining the antibacterial activity and eukaryotic toxicity of HDP mimics. Most examples have utilized primary amines or guanidines as the source of positively charged moieties, inspired by the lysine and arginine residues in HDPs. Here, we explore the impact of amine group variation (primary, secondary, or tertiary amine) on the antibacterial performance of HDP-mimicking β-peptide polymers. Our studies show that a secondary ammonium is superior to either a primary ammonium or a tertiary ammonium as the cationic moiety in antibacterial β-peptide polymers. The optimal polymer, a homopolymer bearing secondary amino groups, displays potent antibacterial activity and the highest selectivity (low hemolysis and cytotoxicity). The optimal polymer displays potent activity against antibiotic-resistant bacteria and high therapeutic efficacy in treating MRSA-induced wound infections and keratitis as well as low acute dermal toxicity and low corneal epithelial cytotoxicity. This work suggests that secondary amines may be broadly useful in the design of antibacterial polymers.

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

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

Rational Design of an Antimicrobial Peptide Based on Structural Insight into the Interaction of Pseudomonas aeruginosa Initiation Factor 1 with Its Cognate 30S Ribosomal Subunit

Bacterial infections continue to represent a major worldwide health hazard following the emergence of drug-resistant pathogenic strains. Pseudomonas aeruginosa is an opportunistic pathogen causing nosocomial infections with increased morbidity and mortality. The increasing antibiotic resistance in P. aeruginosa has led to an unmet need for discovery of new antibiotic candidates. Bacterial protein synthesis is an essential metabolic process and a validated target for antibiotic development; however, the precise structural mechanism in P. aeruginosa remains unknown. In this work, the interaction of P. aeruginosa initiation factor 1 (IF1) with the 30S ribosomal subunit was studied by NMR, which enabled us to construct a structure of IF1-bound 30S complex. A short α-helix in IF1 was found to be critical for IF1 ribosomal binding and function. A peptide derived from this α-helix was tested and displayed a high ability to inhibit bacterial growth. These results provide a clue for rational design of new antimicrobials.

Directed Expression of Tracheal Antimicrobial Peptide as a Treatment for Bovine-Associated Staphylococcus Aureus-Induced Mastitis in Mice

Bovine mastitis is perplexing the dairy industry since the initiation of intensive dairy farming, which has caused a reduction in the productivity of cows and an escalation in costs. The use of antibiotics causes a series of problems, especially the formation of bacterial antimicrobial resistance. However, there are limited antibiotic-free therapeutic strategies that can effectively relieve bacterial infection of bovine mammary glands. Hence, in this study, we constructed a mammary gland tissue-specific expression vector carrying the antimicrobial peptide of bovine-derived tracheal antimicrobial peptide (TAP) and evaluated it in both primary bovine mammary epithelial cells (pBMECs) and mice. The results showed that the vector driven by the β-lactoglobulin gene (BLG) promoter could efficiently direct the expression of TAP in pBMECs and the mammary gland tissue of mice. In addition, significant antibacterial effects were observed in both in vitro and in vivo experiments when introducing this vector to bovine-associated Staphylococcus aureus-treated pBMECs and mice, respectively. This study demonstrated that the mammary gland tissue-specific expression vector could be used to introduce antimicrobial peptide both in in vitro and in vivo and will provide a new therapeutic strategy in the treatment of bovine mastitis.

Mechanism of Antimicrobial Peptides: Antimicrobial, Anti-Inflammatory and Antibiofilm Activities

Antimicrobial peptides (AMPs) are regarded as a new generation of antibiotics. Besides antimicrobial activity, AMPs also have antibiofilm, immune-regulatory, and other activities. Exploring the mechanism of action of AMPs may help in the modification and development of AMPs. Many studies were conducted on the mechanism of AMPs. The present review mainly summarizes the research status on the antimicrobial, anti-inflammatory, and antibiofilm properties of AMPs. This study not only describes the mechanism of cell wall action and membrane-targeting action but also includes the transmembrane mechanism of intracellular action and intracellular action targets. It also discusses the dual mechanism of action reported by a large number of investigations. Antibiofilm and anti-inflammatory mechanisms were described based on the formation of biofilms and inflammation. This study aims to provide a comprehensive review of the multiple activities and coordination of AMPs in vivo, and to fully understand AMPs to realize their therapeutic prospect.

A Concise Synthetic Strategy Towards the Novel Calcium-dependent Lipopeptide Antibiotic, Malacidin A and Analogues

Malacidin A is a novel calcium-dependent lipopeptide antibiotic with excellent activity against Gram-positive pathogens. Herein, a concise and robust synthetic route toward malacidin A is reported, employing 9-fluorenylmethoxycarbonyl solid-phase peptide synthesis of a linear precursor, including late-stage incorporation of the lipid tail, followed by solution-phase cyclization. The versatility of this synthetic strategy was further demonstrated by synthesis of a diastereomeric variant of malacidin A and a small library of simplified analogues with variation of the lipid moiety.

Biomedical Relevance of Novel Anticancer Peptides in the Sensitive Treatment of Cancer

The global increase in cancer mortality and economic losses necessitates the cautious quest for therapeutic agents with compensatory advantages over conventional therapies. Anticancer peptides (ACPs) are a subset of host defense peptides, also known as antimicrobial peptides, which have emerged as therapeutic and diagnostic candidates due to several compensatory advantages over the non-specificity of the current treatment regimens. This review aimed to highlight the ravaging incidence of cancer, the use of ACPs in cancer treatment with their mechanisms, ACP discovery and delivery methods, and the limitations for their use. This would create awareness for identifying more ACPs with better specificity, accuracy and sensitivity towards the disease. It would also promote their efficacious utilization in biotechnology, medical sciences and molecular biology to ease the severity of the disease and enable the patients living with these conditions to develop an accommodating lifestyle.

D-Amino Acid-Containing Lipopeptides Derived from the Lead Peptide BP100 with Activity against Plant Pathogens

From a previous collection of lipopeptides derived from BP100, we selected 18 sequences in order to improve their biological profile. In particular, analogues containing a D-amino acid at position 4 were designed, prepared, and tested against plant pathogenic bacteria and fungi. The biological activity of these sequences was compared with that of the corresponding parent lipopeptides with all L-amino acids. In addition, the influence of the length of the hydrophobic chain on the biological activity was evaluated. Interestingly, the incorporation of a D-amino acid into lipopeptides bearing a butanoyl or a hexanoyl chain led to less hemolytic sequences and, in general, that were as active or more active than the corresponding all L-lipopeptides. The best lipopeptides were BP475 and BP485, both incorporating a D-Phe at position 4 and a butanoyl group, with MIC values between 0.8 and 6.2 µM, low hemolysis (0 and 24% at 250 µM, respectively), and low phytotoxicity. Characterization by NMR of the secondary structure of BP475 revealed that the D-Phe at position 4 disrupts the α-helix and that residues 6 to 10 are able to fold in an α-helix. This secondary structure would be responsible for the high antimicrobial activity and low hemolysis of this lipopeptide.

Synthetic Peptides Derived From Lycosa Erythrognatha Venom: Interaction With Phospholipid Membranes and Activity Against Resistant Bacteria

Superbugs are a public health problem, increasing the need of new drugs and strategies to combat them. Our group has previously identified LyeTxI, an antimicrobial peptide isolated from Lycosa erythrognatha spider venom. From LyeTxI, we synthesized and characterized a derived peptide named LyeTxI-b, which has shown significant in vitro and in vivo activity. In this work, we elucidate the interaction of LyeTxI-b with artificial membranes as well as its effects on resistant strains of bacteria in planktonic conditions or biofilms. Isothermal titration calorimetry revealed that LyeTxI-b interacts more rapidly and with higher intensity with artificial vesicles, showing higher affinity to anionic vesicles, when compared to synthetic LyeTxI. In calcein experiments, LyeTxI-b caused greater levels of vesicle cleavage. Both peptides showed antibacterial activity at concentrations of μmol L⁻¹ against 12 different clinically isolated strains, in planktonic conditions, in a concentration-dependent manner. Furthermore, both peptides elicited a dose-dependent production of reactive oxygen species in methicillin-resistant Staphylococcus aureus. In S. aureus biofilm assay, LyeTxI-b was more potent than LyeTxI. However, none of these peptides reduced Escherichia coli biofilms. Our results show LyeTxI-b as a promising drug against clinically resistant strains, being a template for developing new antibiotics.