Antimicrobial peptides (AMPs): A promising class of antimicrobial compounds

Detection strategies of infectious diseases via peptide-based electrochemical biosensors

Infectious diseases have threatened human life for as long as humankind has existed. One of the most crucial aspects of fighting against these infections is diagnosis to prevent disease spread. However, traditional diagnostic methods prove insufficient and time-consuming in the face of a pandemic. Therefore, studies focusing on detecting viruses causing these diseases have increased, with a particular emphasis on developing rapid, accurate, specific, user-friendly, and portable electrochemical biosensor systems. Peptides are used integral components in biosensor fabrication for several reasons, including various and adaptable synthesis protocols, long-term stability, and specificity. Here, we discuss peptide-based electrochemical biosensor systems that have been developed over the last decade for the detection of infectious diseases. In contrast to other reports on peptide-based biosensors, we have emphasized the following points i) the synthesis methods of peptides for biosensor applications, ii) biosensor fabrication approaches of peptide-based electrochemical biosensor systems, iii) the comparison of electrochemical biosensors with other peptide-based biosensor systems and the advantages and limitations of electrochemical biosensors, iv) the pros and cons of peptides compared to other biorecognition molecules in the detection of infectious diseases, v) different perspectives for future studies with the shortcomings of the systems developed in the past decade.

LL-37_Renalexin hybrid peptide exhibits antimicrobial activity at lower MICs than its counterpart single peptides

An alarming global public health and economic peril has been the emergence of antibiotic resistance resulting from clinically relevant bacteria pathogens, including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumonia, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species constantly exhibiting intrinsic and extrinsic resistance mechanisms against last-resort antibiotics like gentamycin, ciprofloxacin, tetracycline, colistin, and standard ampicillin prescription in clinical practices. The discovery and applications of antimicrobial peptides (AMPs) with antibacterial properties have been considered and proven as alternative antimicrobial agents to antibiotics. In this study, we have designed, produced, and purified a recombinant novel multifunctional hybrid antimicrobial peptide LL-37_Renalexin for the first time via the application of newly designed flexible GS peptide linker coupled with the use of our previously characterized small metal-binding proteins SmbP and CusF3H+ as carrier proteins that allow for an enhanced bacterial expression, using BL21(DE3) and SHuffle T7(DE3) Escherichia coli strains, and purification of the hybrid peptide via immobilized metal affinity chromatography. The purified tag-free LL-37_Renalexin hybrid peptide exhibited above 85% reduction in bacteria colony-forming units and broad-spectrum antimicrobial effects against Staphylococcus aureus, Escherichia coli, Methicillin-resistant Staphylococcus aureus (MRSA), and Klebsiella pneumoniae bacteria clinical isolates at a lower minimum inhibition concentration level (10-33 μM) as compared to its counterpart single-AMPs LL-37 and Renalexin (50-100 μM). KEY POINTS: • The hybrid antimicrobial peptide LL-37_Renalexin has been designed using a GS linker. • The peptide was expressed with the carrier proteins SmbP and CusF3H+. • The hybrid peptide shows antibacterial potency against clinical bacterial isolates.

Beyond the venom: Exploring the antimicrobial peptides from Androctonus species of scorpion

Prevalent worldwide, the Androctonus scorpion genus contributes a vital role in scorpion envenoming. While diverse scorpionisms are observed because of several different species, their secretions to protect themselves have been identified as a potent source of antimicrobial peptide (AMP)-like compounds. Distinctly, the venom of these species contains around 24 different AMPs, with definite molecules studied for their therapeutic potential as antimicrobial, antifungal, antiproliferative and antiangiogenic agents. Our review focuses on the therapeutic potential of native and synthetic AMPs identified so far in the Androctonus scorpion genus, identifying research gaps in peptide therapeutics and guiding further investigations. Certain AMPs have demonstrated remarkable compatibility to be prescribed as anticancer drug to reduce cancer cell proliferation and serve as a potent antibiotic alternative. Besides, analyses were performed to explore the characteristics and affinities of peptides for membranes. Overall, the study of AMPs derived from the Androctonus scorpion genus provides valuable insights into their potential applications in medicine and drug development.

Bioinorganic Chemistry Meets Microbiology: Copper(II) and Zinc(II) Complexes Doing the Cha-Cha with the C-t-CCL-28 Peptide, Dancing till the End of Microbes

The necessity to move away from conventional antibiotic therapy has sparked interest in antimicrobial peptides (AMPs). One fascinating example is human CCL-28 chemokine produced by acinar epithelial cells in the salivary glands. It can also be released into the oral cavity with saliva, playing a crucial role in oral protection. The C-terminal domain of CCL-28 possesses antifungal and antibacterial properties, which are likely linked to membrane disruption and enzyme leakage. Studies suggest that AMPs can become more potent after they have bound Cu(II) or Zn(II). In many cases, these ions are essential for maximizing effectiveness by altering the peptides' physicochemical properties, such as their local charge or structure. The examined peptide binds Cu(II) and Zn(II) ions very effectively, forming equimolar complexes. Metal ion binding affinity, coordination mode, and antimicrobial activity strongly depend on the pH of the environment. Coordination modes have been proposed based on the results of potentiometric titrations, spectroscopic studies (UV-visible, electron paramagnetic resonance and circular dichroism at different path lengths), and mass spectrometry. The antimicrobial properties of the Cu(II) and Zn(II) complexes with the C-terminal fragment of CCL-28 chemokine have been assessed against fungal and bacterial strains, demonstrating exceptional activity against Candida albicans at pH 5.4. Moreover, the complex with Zn(II) ions shows the same activity against theStreptococcus mutans bacterium as chloramphenicol, a commonly used antibiotic. Cyclic voltammetry proposed a probable antimicrobial mechanism of the studied Cu(II) complex through the formation of reactive oxygen species, which was also confirmed by tests with ascorbic acid in UV-vis and fluorescence spectroscopic studies.

How Unnatural Amino Acids in Antimicrobial Peptides Change Interactions with Lipid Model Membranes

This study investigates the potential of antimicrobial peptides (AMPs) as alternatives to combat antibiotic resistance, with a focus on two AMPs containing unnatural amino acids (UAAs), E2-53R (16 AAs) and LE-54R (14 AAs). In both peptides, valine is replaced by norvaline (Nva), and tryptophan is replaced by 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic). Microbiological studies reveal their potent activity against both Gram-negative (G(-)) and Gram-positive (G(+)) bacteria without any toxicity to eukaryotic cells at test concentrations up to 32 μM. Circular dichroism (CD) spectroscopy indicates that these peptides maintain α-helical structures when interacting with G(-) and G(+) lipid model membranes (LMMs), a feature linked to their efficacy. X-ray diffuse scattering (XDS) demonstrates a softening of G(-), G(+) and eukaryotic (Euk33) LMMs and a nonmonotonic decrease in chain order as a potential determinant for bacterial membrane destabilization. Additionally, XDS finds a significant link between both peptides' interfacial location in G(-) and G(+) LMMs and their efficacy. Neutron reflectometry (NR) confirms the AMP locations determined using XDS. Lack of toxicity in eukaryotic cells may be related to their loss of α-helicity and their hydrocarbon location in Euk33 LMMs. Both AMPs with UAAs offer a novel strategy to wipe out antibiotic-resistant strains while maintaining human cells. These findings are compared with previously published data on E2-35, which consists of the natural amino acids arginine, tryptophan, and valine.

An insight into structure-activity relationships in subclass IIb bacteriocins: Plantaricin EvF

This study reports the structure-activity relationships of a unique subclass IIb bacteriocin, plantaricin EvF, which consists of two peptide chains and possesses potent antimicrobial activity. Because the plantaricin Ev peptide chain lacks an α-helix structure, plantaricin EvF is unable to exert its antimicrobial activity through helix-helix interactions like typical subclass IIb bacteriocins. We have shown by various structural evaluation methods that plantaricin Ev can be stabilized by hydrogen bonding at amino acid residues R3, V12, and R13 to the N-terminal region of plantaricin F. This binding gives plantaricin EvF a special spade-shaped structure that exerts antimicrobial activity. In addition, the root-mean-square deviations (RMSDs) of the amino acid residues Y6, F8, and R13 of plantaricin Ev pre- and post-binding were 1.512, 1.723, and 1.369, respectively, indicating that they underwent large structural changes. The alanine scanning experiments demonstrated the important role of the above key amino acids in maintaining the structural integrity of plantaricin EvF. This study not only reveals the unique structural features of plantaricin EvF, but also provides an insight into the structure-activity relationships of subclass IIb bacteriocins.

StackDPPred: Multiclass prediction of defensin peptides using stacked ensemble learning with optimized features

Host defense or antimicrobial peptides (AMPs) are promising candidates for protecting host against microbial pathogens for example bacteria, virus, fungi, yeast. Defensins are the type of AMPs that act as potential therapeutic drug agent and perform vital role in various biological process. Conventional Experiments to identify defensin peptides (DPs) are time consuming and expensive. Thus, the shortcomings of wet lab experiments are leveraged by computational methods to accurately predict the functional types of DPs. In this paper, we aim to propose a novel multi-class ensemble-based prediction model called StackDPPred for identifying the properties of DPs. The peptide sequences are encoded using split amino acid composition (SAAC), segmented position specific scoring matrix (SegPSSM), histogram of oriented gradients-based PSSM (HOGPSSM) and feature extraction based graphical and statistical (FEGS) descriptors. Next, principal component analysis (PCA) is used to select the best subset of attributes. After that, the optimized features are fed into single machine learning and stacking-based ensemble classifiers. Furthermore, the ablation study demonstrates the robustness and efficacy of the stacking approach using reduced features for predicting DPs and their families. The proposed StackDPPred method improves the overall accuracy by 13.41% and 7.62% compared to existing DPs predictors iDPF-PseRAAC and iDEF-PseRAAC, respectively on validation test. Additionally, we applied the local interpretable model-agnostic explanations (LIME) algorithm to understand the contribution of selected features to the overall prediction. We believe, StackDPPred could serve as a valuable tool accelerating the screening of large-scale DPs and peptide-based drug discovery process.

Using gold-based nanomaterials for fighting pathogenic bacteria: from detection to therapy

Owing to the unique quantum size effect and surface effect, gold-based nanomaterials (GNMs) are promising for pathogen detection and broad-spectrum antimicrobial activity. This review summarizes recent research on GNMs as sensors for detecting pathogens and as tools for their elimination. Firstly, the need for pathogen detection is briefly introduced with an overview of the physicochemical properties of gold nanomaterials. And then strategies for the application of GNMs in pathogen detection are discussed. Colorimetric, fluorescence, surface-enhanced Raman scattering (SERS) techniques, dark-field microscopy detection and electrochemical methods can enable efficient, sensitive, and specific pathogen detection. The third section describes the antimicrobial applications of GNMs. They can be used for antimicrobial agent delivery and photothermal conversion and can act synergistically with photosensitizers to achieve the precise killing of pathogens. In addition, GNMs are promising for integrated pathogen detection and treatment; for example, combinations of colorimetric or SERS detection with photothermal sterilization have been demonstrated. Finally, future outlooks for the applications of GNMs in pathogen detection and treatment are summarized.

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.

ProT-Diff: A Modularized and Efficient Strategy for De Novo Generation of Antimicrobial Peptide Sequences by Integrating Protein Language and Diffusion Models

Antimicrobial peptides (AMPs) are a promising solution for treating antibiotic-resistant pathogens. However, efficient generation of diverse AMPs without prior knowledge of peptide structures or sequence alignments remains a challenge. Here, ProT-Diff is introduced, a modularized deep generative approach that combines a pretrained protein language model with a diffusion model for the de novo generation of AMPs sequences. ProT-Diff generates thousands of AMPs with diverse lengths and structures within a few hours. After silico physicochemical screening, 45 peptides are selected for experimental validation. Forty-four peptides showed antimicrobial activity against both gram-positive or gram-negative bacteria. Among broad-spectrum peptides, AMP_2 exhibited potent antimicrobial activity, low hemolysis, and minimal cytotoxicity. An in vivo assessment demonstrated its effectiveness against a drug-resistant E. coli strain in acute peritonitis. This study not only introduces a viable and user-friendly strategy for de novo generation of antimicrobial peptides, but also provides potential antimicrobial drug candidates with excellent activity. It is believed that this study will facilitate the development of other peptide-based drug candidates in the future, as well as proteins with tailored characteristics.

Exploring Antimicrobial Potency, ADMET, and Optimal Drug Target of a Non-ribosomal Peptide Sevadicin from Bacillus pumilus, through In Vitro Assay and Molecular Dynamics Simulation

The current study was designed to explore the biosynthetic potential of sevadicin in Bacillus pumilus species and its interaction with bacterial drug target molecules. The non-ribosomal peptide (NRP) cluster in B. pumilus SF-4 was preliminarily confirmed using PCR-based screening, and the bioactivity of strain SF-4 culture extract was assessed against a set of human pathogenic strains. The susceptibility assay showed that strain SF-4 extract had higher inhibitory concentrations (312-375 µg/mL) than ciprofloxacin. Genome mining of B. pumilus strains (n = 22) using AntiSMASH and BAGEL identified sevadicin coding biosynthetic gene cluster only in strain SF-4, constitutes of two core biosynthetic genes, three additional biosynthetic genes, two transport-related genes, and one regulatory gene. The molecular docking of sevadicin with various putative bacterial drug targets such as dihydropteroate, muramyl ligase E, topoisomerase, penicillin-binding protein, and in vitro safety analyses were conducted with detailed ADMET screening. The results showed that sevadicin makes hydrophobic interaction with MurE (PDB ID: 1E8C and 4C13) via hydrogen bonding, suggesting bacterial growth inhibition by disrupting the cell wall synthesis pathway and exhibiting a secure biosafety profile. The stability and compactness of sevadicin/MurE complexes were assessed via molecular dynamic simulation using RMSD, RMSF, and Rg. The simulation results revealed the binding stability of sevadicin/MurE complexes and indicated that the complexes can't be easily deformed. In conclusion, the current study explored the biosynthesis of sevadicin in B. pumilus for the first time and found that sevadicin inhibits bacterial growth by inhibiting cell wall synthesis via targeting the MurE enzyme and exhibits no toxicity.

Antimicrobial peptide-based strategies to overcome antimicrobial resistance

Antibiotic resistance has emerged as a global threat, rendering the existing conventional treatment strategies ineffective. In view of this, antimicrobial peptides (AMPs) have proven to be potent alternative therapeutic interventions with a wide range of applications in clinical health. AMPs are small peptides produced naturally as a part of the innate immune responses against a broad range of bacterial, fungal and viral pathogens. AMPs present a myriad of advantages over traditional antibiotics, including their ability to target multiple sites, reduced susceptibility to resistance development, and high efficacy at low doses. These peptides have demonstrated notable potential in inhibiting microbes resistant to traditional antibiotics, including the notorious ESKAPE pathogens, recognized as the primary culprits behind nosocomial infections. AMPs, with their multifaceted benefits, emerge as promising candidates in the ongoing efforts to combat the escalating challenges posed by antibiotic resistance. This in-depth review provides a detailed discussion on AMPs, encompassing their classification, mechanism of action, and diverse clinical applications. Focus has been laid on combating newly emerging drug-resistant organisms, emphasizing the significance of AMPs in mitigating this pressing challenge. The review also illuminates potential future strategies that may be implemented to improve AMP efficacy, such as structural modifications and using AMPs in combination with antibiotics and matrix-inhibiting compounds.

Glioblastoma Multiforme: Sensitivity to Antimicrobial Peptides LL-37 and PG-1, and Their Combination with Chemotherapy for Predicting the Overall Survival of Patients

Background/Objectives: Glioblastomas (GBMs) are the most malignant and intractable of all cancers, with an unfavorable clinical prognosis for affected patients. The objective was to analyze the sensitivity of GBM cells to the antimicrobial peptides (AMPs) cathelicidin (LL-37) and protegrin-1 (PG-1), both alone and in combination with chemotherapy, to predict overall survival (OS) in the patients. Methods: The study was conducted on 27 GBM patients treated in the neurosurgical department of the Almazov Medical Research Centre (Saint Petersburg, Russia) from 2021 to 2024. The cytotoxic effects of chemotherapy, AMPs, and their combinations on brain tumor cells were assessed by an MTT assay using a 50% inhibitory concentration (IC50). Results: In GBM cells from the patients, LL-37 and PG-1 exhibited strong anticancer effects, surpassing those of chemotherapy drugs. These LL-37 and PG-1 anticancer effects were associated with a statistically significant increase in life expectancy and OS in GBM patients. These findings were confirmed by experiments on rats with C6 glioma, where the intranasal administration of LL-37 (300 μM) and PG-1 (600 μM) increased the life expectancy of the animals to 69 and 55 days, respectively, compared to 24 days in the control group (HR = 4.139, p = 0.0005; HR = 2.542, p = 0.0759). Conclusions: Additionally, the combination of LL-37 and PG-1 with chemotherapy drugs showed that a high IC50 of LL-37 with cisplatin (cutoff > 800 μM) in GBM cells was associated with increased life expectancy (19 vs. 5 months, HR = 4.708, p = 0.0101) and OS in GBM patients. These combinations could be used in future GBM treatments.

Novel antimicrobial peptides based on Protegrin-1: In silico and in vitro assessments

The development of antibiotic resistance has caused significant health problems. Antimicrobial peptides (AMPs) are considered next-generation antibiotics. Protegrin-1 (PG-1) is a β-hairpin AMP with a membrane-binding capacity. This study used twelve PG-1 analogs with different amino acid substitutions. Coarse-grained molecular dynamics (MD) simulations were used to assess these analogs, and their physicochemical properties were computed using the Antimicrobial Peptide Database. Three AMPs, PEP-D, PEP-C, and PEP-H, were chosen and synthesized for antibacterial testing. The microbroth dilution technique and hemolytic assays evaluated the antimicrobial efficacy and cellular toxicity. The checkerboard method was used to test the combined activity of AMP and standard antibiotics. Cell membrane permeability and electron microscopy were used to evaluate the mode of action. The chemical stability of the selective AMP, PEP-D, was assessed by a validated HPLC method. PEP-D consists of 16-18 amino acid residues and has a charge of +7 and a hydrophobicity of 44 %, similar to PG-1. It can efficiently inactivate bacteria by disrupting cell membranes and significantly reducing hemolytic activity. Chemical stability studies indicated that AMP was stable at 40 °C for six months under autoclave conditions. This study could introduce the potential therapeutic application of selective AMP as an anti-infective agent.

Dual-Action Therapeutics: DNA Alkylation and Antimicrobial Peptides for Cancer Therapy

Cancer remains one of the most difficult diseases to treat, requiring continuous research into innovative therapeutic strategies. Conventional treatments such as chemotherapy and radiotherapy are effective to a certain extent but often have significant side effects and carry the risk of resistance. In recent years, the concept of dual-acting therapeutics has attracted considerable attention, particularly the combination of DNA alkylating agents and antimicrobial peptides. DNA alkylation, a well-known mechanism in cancer therapy, involves the attachment of alkyl groups to DNA, leading to DNA damage and subsequent cell death. Antimicrobial peptides, on the other hand, have been shown to be effective anticancer agents due to their ability to selectively disrupt cancer cell membranes and modulate immune responses. This review aims to explore the synergistic potential of these two therapeutic modalities. It examines their mechanisms of action, current research findings, and the promise they offer to improve the efficacy and specificity of cancer treatments. By combining the cytotoxic power of DNA alkylation with the unique properties of antimicrobial peptides, dual-action therapeutics may offer a new and more effective approach to fighting cancer.

The Archetypal Gamma-Core Motif of Antimicrobial Cys-Rich Peptides Inhibits H+-ATPases in Target Pathogens

Human lactoferrin (hLf) is an innate host defense protein that inhibits microbial H+-ATPases. This protein includes an ancestral structural motif (i.e., γ-core motif) intimately associated with the antimicrobial activity of many natural Cys-rich peptides. Peptides containing a complete γ-core motif from hLf or other phylogenetically diverse antimicrobial peptides (i.e., afnA, SolyC, PA1b, PvD1, thanatin) showed microbicidal activity with similar features to those previously reported for hLf and defensins. Common mechanistic characteristics included (1) cell death independent of plasma membrane (PM) lysis, (2) loss of intracellular K+ (mediated by Tok1p K+ channels in yeast), (3) inhibition of microbicidal activity by high extracellular K+, (4) influence of cellular respiration on microbicidal activity, (5) involvement of mitochondrial ATP synthase in yeast cell death processes, and (6) increment of intracellular ATP. Similar features were also observed with the BM2 peptide, a fungal PM H+-ATPase inhibitor. Collectively, these findings suggest host defense peptides containing a homologous γ-core motif inhibit PM H+-ATPases. Based on this discovery, we propose that the γ-core motif is an archetypal effector involved in the inhibition of PM H+-ATPases across kingdoms of life and contributes to the in vitro microbicidal activity of Cys-rich antimicrobial peptides.

Advancements in peptide-based antimicrobials: A possible option for emerging drug-resistant infections

In recent years, multidrug-resistant pathogenic microorganisms (MDROs) have emerged as a severe threat to human health, exhibiting robust resistance to traditional antibiotics. This has created a formidable challenge in modern medicine as we grapple with limited options to combat these resilient bacteria. Despite extensive efforts by scientists to develop new antibiotics targeting these pathogens, the quest for novel antibacterial molecules has become increasingly arduous. Fortunately, nature offers a potential solution in the form of cationic antimicrobial peptides (AMPs) and their synthetic counterparts. AMPs, naturally occurring peptides, have displayed promising efficacy in fighting bacterial infections by disrupting bacterial cell membranes, hindering their survival and reproduction. These peptides, along with their synthetic mimics, present an exciting alternative in combating antibiotic resistance. They hold the potential to emerge as a formidable tool against MDROs, offering hope for improved strategies to protect communities. Extensive research has explored the diversity, history, and structure-properties relationship of AMPs, investigating their amphiphilic nature for membrane disruption and mechanisms of action. However, despite their therapeutic promise, AMPs face several documented limitations. Among these challenges, poor pharmacokinetic properties stand out, impeding the attainment of therapeutic levels in the body. Additionally, some AMPs exhibit toxicity and susceptibility to protease cleavage, leading to a short half-life and reduced efficacy in animal models. These limitations pose obstacles in developing effective treatments based on AMPs. Furthermore, the high manufacturing costs associated with AMPs could significantly hinder their widespread use. In this review, we aim to present experimental and theoretical insights into different AMPs, focusing specifically on antibacterial peptides (ABPs). Our goal is to offer a concise overview of peptide-based drug candidates, drawing from a wide array of literature and peer-reviewed studies. We also explore recent advancements in AMP development and discuss the challenges researchers face in moving these molecules towards clinical trials. Our main objective is to offer a comprehensive overview of current AMP and ABP research to guide the development of more precise and effective therapies for bacterial infections.

Cyclization increases bactericidal activity of arginine-rich cationic cell-penetrating peptide for Neisseria gonorrhoeae

We previously reported that a linear cationic 12-amino acid cell-penetrating peptide (CPP) was bactericidal for Neisseria gonorrhoeae. In this study, our objectives were to determine the effect of cyclization of the linear CPP on its antibacterial activity for N. gonorrhoeae and cytotoxicity for human cells. We compared the bactericidal effect of 4-hour treatment with the linear CPP to that of CPPs cyclized by a thioether or a disulfide bond on human challenge and multi-drug resistant (MDR) strains of N. gonorrhoeae grown in cell culture media with 10% fetal bovine serum (FBS). The effect of lipooligosaccharide (LOS) sialylation on bactericidal activity was analyzed. We determined the ability of the CPPs to treat human cells infected in vitro with N. gonorrhoeae, to reduce the inflammatory response of human monocytic cells to gonococci, to kill strains of three commensal Neisseria species, and to inhibit gonococcal biofilms. The cyclized CPPs killed 100% of gonococci from all strains at 100 µM and >90% at 20 µM and were more potent than the linear form. The thioether-linked but not the disulfide-linked CPP was less cytotoxic for human cervical cells compared to the linear CPP. LOS sialylation had minimal effect on bactericidal activity. In treating infected human cells, the thioether-linked CPP at 20 µM killed >60% of extra- and intracellular bacteria and reduced TNF-α expression by THP-1 cells. The potency of the CPPs for the pathogenic and the commensal Neisseria was similar. The thioether-linked CPP partially eradicated gonococcal biofilms. Future studies will focus on determining efficacy in the female mouse model of gonorrhea.IMPORTANCENeisseria gonorrhoeae remains a major cause of sexually transmitted infections with 82 million cases worldwide in 2020, and 710,151 confirmed cases in the US in 2021, up 25% from 2017. N. gonorrhoeae can infect multiple tissues including the urethra, cervix, rectum, pharynx, and conjunctiva. The most serious sequelae are suffered by infected women as gonococci ascend to the upper reproductive tract and cause pelvic inflammatory disease, chronic pelvic pain, and infertility in 10%-20% of women. Control of gonococcal infection is widely recognized as increasingly challenging due to the lack of any vaccine. N. gonorrhoeae has quickly developed resistance to all but one class of antibiotics and the emergence of multidrug-resistant strains could result in untreatable infections. As such, gonorrhea is classified by the Center for Disease Control (CDC) as an urgent public health threat. The research presented herein on new therapeutics for gonorrhea has identified a cyclic cell-penetrating peptide (CPP) as a potent molecule targeting N. gonorrhoeae.

The Roadmap of Plant Antimicrobial Peptides Under Environmental Stress: From Farm to Bedside

Antimicrobial peptides (AMPs) are the most favorable alternatives in overcoming multidrug resistance, alone or synergistically with conventional antibiotics. Plant-derived AMPs, as cysteine-rich peptides, widely compensate the pharmacokinetic drawbacks of peptide therapeutics. Compared to the putative genes encrypted in the genome, AMPs that are produced under stress are active forms with the ability to combat resistant microbial species. Within this study, plant-derived AMPs, namely, defensins, nodule-specific cysteine-rich peptides, snakins, lipid transfer proteins, hevein-like proteins, α-hairpinins, and aracins, expressed under biotic and abiotic stresses, are classified. We could observe that while α-hairpinins and snakins display a helix-turn-helix structure, conserved motif patterns such as β1αβ2β3 and β1β2β3 exist in plant defensins and hevein-like proteins, respectively. According to the co-expression data, several plant AMPs are expressed together to trigger synergistic effects with membrane disruption mechanisms such as toroidal pore, barrel-stave, and carpet models. The application of AMPs as an eco-friendly strategy in maintaining agricultural productivity through the development of transgenes and bio-pesticides is discussed. These AMPs can be consumed in packaging material, wound-dressing products, coating catheters, implants, and allergology. AMPs with cell-penetrating properties are verified for the clearance of intracellular pathogens. Finally, the dominant pharmacological activities of bioactive peptides derived from the gastrointestinal digestion of plant AMPs, namely, inhibitors of renin and angiotensin-converting enzymes, dipeptidyl peptidase IV and α-glucosidase inhibitors, antioxidants, anti-inflammatory, immunomodulating, and hypolipidemic peptides, are analyzed. Conclusively, as phytopathogens and human pathogens can be affected by plant-derived AMPs, they provide a bright perspective in agriculture, breeding, food, cosmetics, and pharmaceutical industries, translated as farm to bedside.

Antimicrobial peptides derived from food byproducts: Sources, production, purification, applications, and challenges

Food wastes can be a valuable reservoir of bioactive substances that can serve as natural preservatives in foods or as functional ingredients with potential health benefits. The antimicrobial properties of protein hydrolysates, especially antimicrobial peptides (AMPs) derived from food byproducts (FBs), have been extensively explored. These protein fragments are defined by their short length, low molecular weight, substantial content of hydrophobic and basic amino acids, and positive net charge. The intricate mechanisms by which these peptides exert their antimicrobial effects on microorganisms and pathogens have been elaborately described. This review also focuses on techniques for producing and purifying AMPs from diverse FBs, including seafood, livestock, poultry, plants, and dairy wastes. According to investigations, incorporating AMPs as additives and alternatives to chemical preservatives in food formulations and packaging materials has been pursued to enhance both consumer health and the shelf life of foods and their products. However, challenges associated with the utilization of AMPs derived from food waste depend on their interaction with the food matrix, acceptability, and commercial viability. Overall, AMPs can serve as alternative safe additives, thereby ensuring the safety and prolonging the storage duration of food products based on specific regulatory approvals as recommended by the respective safety authorities.

Antibiotics: From Mechanism of Action to Resistance and Beyond

Antibiotics are the super drugs that have revolutionized modern medicine by curing many infectious diseases caused by various microbes. They efficiently inhibit the growth and multiplication of the pathogenic microbes without causing adverse effects on the host. However, prescribing suboptimal antibiotic and overuse in agriculture and animal husbandry have led to the emergence of antimicrobial resistance, one of the most serious threats to global health at present. The efficacy of a new antibiotic is high when introduced; however, a small bacterial population attains resistance gradually and eventually survives. Understanding the mode of action of these miracle drugs, as well as their interaction with targets is very complex. However, it is necessary to fulfill the constant need for novel therapeutic alternatives to address the inevitable development of resistance. Therefore, considering the need of the hour, this article has been prepared to discuss the mode of action and recent advancements in the field of antibiotics. Efforts has also been made to highlight the current scenario of antimicrobial resistance and drug repurposing as a fast-track solution to combat the issue.

Genetically encoded libraries and spider venoms as emerging sources for crop protective peptides

Agricultural crops are targeted by various pathogens (fungi, bacteria, and viruses) and pests (herbivorous arthropods). Antimicrobial and insecticidal peptides are increasingly recognized as eco-friendly tools for crop protection due to their low propensity for resistance development and the fact that they are fully biodegradable. However, historical challenges have hindered their development, including poor stability, limited availability, reproducibility issues, high production costs, and unwanted toxicity. Toxicity is a primary concern because crop-protective peptides interact with various organisms of environmental and economic significance. This review focuses on the potential of genetically encoded peptide libraries like the use of two-hybrid-based methods for antimicrobial peptides identification and insecticidal spider venom peptides as two main approaches for targeting plant pathogens and pests. We discuss some key findings and challenges regarding the practical application of each strategy. We conclude that genetically encoded peptide library- and spider venom-derived crop protective peptides offer a sustainable and environmentally responsible approach for addressing modern crop protection needs in the agricultural sector.

Epinecidin-1 and lactic acid synergistically inhibit Aeromonas hydrophila through membrane disruption

Epinecidin-1 (Epi-1) is an antimicrobial peptide originated from fish with various pharmacological activities but carries the risk of acquiring resistance with long-term use. In the present study, we use L-lactic acid to enhance the antibacterial activity of synthesized Epi-1 against the aquaculture and food pathogen Aeromonas hydrophila. The results showed that 5.5 mmol/L lactic acid increased the inhibitory and bactericidal activity of 25 μmol/L Epi-1 against two strains of A. hydrophila. The laser confocal images proved that lactic acid pre-treatment improved the attachment efficiency of Epi-1 in A.hydrophila cells. In addition, lactic acid enhanced the damaging effect of Epi-1 on the cell membrane of A. hydrophila, evidenced by releasing more nucleic acids, proteins, and transmembrane pH ingredients decrease and electromotive force dissipation. SEM images showed that compared with the single Epi-1 treatment, the co-treatment of Epi-1 and lactic acid caused more outer membrane vesicles (OMVs) and more severe cell deformation. These findings proved that lactic acid could enhance the efficiency of Epi-1 against A. hydrophila and shed light on new aspects to avoid resistance of pathogens against Epi-1.

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

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

Plant-Derived Antimicrobials and Their Crucial Role in Combating Antimicrobial Resistance

Antibiotic resistance emerged shortly after the discovery of the first antibiotic and has remained a critical public health issue ever since. Managing antibiotic resistance in clinical settings continues to be challenging, particularly with the rise of superbugs, or bacteria resistant to multiple antibiotics, known as multidrug-resistant (MDR) bacteria. This rapid development of resistance has compelled researchers to continuously seek new antimicrobial agents to curb resistance, despite a shrinking pipeline of new drugs. Recently, the focus of antimicrobial discovery has shifted to plants, fungi, lichens, endophytes, and various marine sources, such as seaweeds, corals, and other microorganisms, due to their promising properties. For this review, an extensive search was conducted across multiple scientific databases, including PubMed, Elsevier, ResearchGate, Scopus, and Google Scholar, encompassing publications from 1929 to 2024. This review provides a concise overview of the mechanisms employed by bacteria to develop antibiotic resistance, followed by an in-depth exploration of plant secondary metabolites as a potential solution to MDR pathogens. In recent years, the interest in plant-based medicines has surged, driven by their advantageous properties. However, additional research is essential to fully understand the mechanisms of action and verify the safety of antimicrobial phytochemicals. Future prospects for enhancing the use of plant secondary metabolites in combating antibiotic-resistant pathogens will also be discussed.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

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.

Food-derived peptides unleashed: emerging roles as food additives beyond bioactivities

Innovating food additives stands as a cornerstone for the sustainable evolution of future food systems. Peptides derived from food proteins exhibit a rich array of physicochemical and biological attributes crucial for preserving the appearance, flavor, texture, and nutritional integrity of foods. Leveraging these peptides as raw materials holds great promise for the development of novel food additives. While numerous studies underscore the potential of peptides as food additives, existing reviews predominantly focus on their biotic applications, leaving a notable gap in the discourse around their abiotic functionalities, such as their physicochemical properties. Addressing this gap, this review offers a comprehensive survey of peptide-derived food additives in food systems, accentuating the application of peptides' abiotic properties. It furnishes a thorough exploration of the underlying mechanisms and diverse applications of peptide-derived food additives, while also delineating the challenges encountered and prospects for future applications. This well-time review will set the stage for a deeper understanding of peptide-derived food additives.

Enhancing Selective Antimicrobial and Antibiofilm Activities of Melittin through 6-Aminohexanoic Acid Substitution

Leucine residues are commonly found in the hydrophobic face of antimicrobial peptides (AMPs) and are crucial for membrane permeabilization, leading to the cell death of invading pathogens. Melittin, which contains four leucine residues, demonstrates broad-spectrum antimicrobial properties but also significant cytotoxicity against mammalian cells. To enhance the cell selectivity of melittin, this study synthesized five analogs by replacing leucine with its structural isomer, 6-aminohexanoic acid. Among these analogs, Mel-LX3 exhibited potent antibacterial activity against both Gram-positive and Gram-negative bacteria. Importantly, Mel-LX3 displayed significantly reduced hemolytic and cytotoxic effects compared to melittin. Mechanistic studies, including membrane depolarization, SYTOX green uptake, FACScan analysis, and inner/outer membrane permeation assays, demonstrated that Mel-LX3 effectively permeabilized bacterial membranes similar to melittin. Notably, Mel-LX3 showed robust antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Pseudomonas aeruginosa (MDRPA). Furthermore, Mel-LX3 effectively inhibited biofilm formation and eradicated existing biofilms of MDRPA. With its improved selective antimicrobial and antibiofilm activities, Mel-LX3 emerges as a promising candidate for the development of novel antimicrobial agents. We propose that the substitution of leucine with 6-aminohexanoic acid in AMPs represents a significant strategy for combating resistant bacteria.

Efflux pump inhibitor chlorpromazine effectively increases the susceptibility of Escherichia coli to antimicrobial peptide Brevinin-2CE

Aim: The response of E. coli ATCC8739 to Brevinin-2CE (B2CE) was evaluated as a strategy to prevent the development of antimicrobial peptide (AMP)-resistant bacteria. Methods: Gene expression levels were detected by transcriptome sequencing and RT-PCR. Target genes were knocked out using CRISPR-Cas9. MIC was measured to evaluate strain resistance. Results: Expression of acrZ and sugE were increased with B2CE stimulation. ATCC8739ΔacrZ and ATCC8739ΔsugE showed twofold and fourfold increased sensitivity, respectively. The survival rate of ATCC8739 was reduced in the presence of B2CE/chlorpromazine (CPZ). Combinations of other AMPs with CPZ also showed antibacterial effects. Conclusion: The results indicate that combinations of AMPs/efflux pump inhibitors (EPIs) may be a potential approach to combat resistant bacteria.

Cascade encapsulation of antimicrobial peptides, exosomes and antibiotics in fibrin-gel for first-aid hemostasis and infected wound healing

Wounding is one of the most common healthcare problems. Bioactive hydrogels have attracted much attention in first-aid hemostasis and wound healing due to their excellent biocompatibility, antibacterial properties, and pro-healing bioactivity. However, their applications are limited by inadequate mechanical properties. In this study, we first prepared edible rose-derived exosome-like nanoparticles (ELNs) and used them to encapsulate antimicrobial peptides (AMP), abbreviated as ELNs(AMP). ELNs(AMP) showed superior intracellular antibacterial activity, 2.5 times greater than AMP, in in vitro cell infection assays. We then prepared and tested an FDA-approved fibrin-gel of fibrinogen and thrombin encapsulating ELNs(AMP) and novobiocin sodium salt (NB) (ELNs(AMP)/NB-fibrin-gels). The fibrin gel showed a sustained release of ELNs(AMP) and NB over the eight days of testing. After spraying onto the skin, the formulation underwent in situ gelation and developed a stable patch with excellent hemostatic performance in a mouse liver injury model with hemostasis in 31 s, only 35.6 % of the PBS group. The fibrin gel exhibited pro-wound healing properties in the mouse-infected skin defect model. The thickness of granulation tissue and collagen of the ELNs(AMP)/NB-fibrin-gels group was 4.00, 6.32 times greater than that of the PBS group. In addition, the ELNs(AMP)/NB-fibrin-gels reduced inflammation (decreased mRNA levels of TNF-α, IL-1β, IL6, MCP1, and CXCL1) at the wound sites and demonstrated a biocompatible and biosafe profile. Thus, we have developed a hydrogel system with excellent hemostatic, antibacterial, and pro-wound healing properties, which may be a candidate for next-generation tissue regeneration with a wide clinical application for first-aid hemostasis and infected wound healing.

AMPActiPred: A three-stage framework for predicting antibacterial peptides and activity levels with deep forest

The emergence and spread of antibiotic-resistant bacteria pose a significant public health threat, necessitating the exploration of alternative antibacterial strategies. Antibacterial peptide (ABP) is a kind of antimicrobial peptide (AMP) that has the potential ability to fight against bacteria infection, offering a promising avenue for developing novel therapeutic interventions. This study introduces AMPActiPred, a three-stage computational framework designed to identify ABPs, characterize their activity against diverse bacterial species, and predict their activity levels. AMPActiPred employed multiple effective peptide descriptors to effectively capture the compositional features and physicochemical properties of peptides. AMPActiPred utilized deep forest architecture, a cascading architecture similar to deep neural networks, capable of effectively processing and exploring original features to enhance predictive performance. In the first stage, AMPActiPred focuses on ABP identification, achieving an Accuracy of 87.6% and an MCC of 0.742 on an elaborate dataset, demonstrating state-of-the-art performance. In the second stage, AMPActiPred achieved an average GMean at 82.8% in identifying ABPs targeting 10 bacterial species, indicating AMPActiPred can achieve balanced predictions regarding the functional activity of ABP across this set of species. In the third stage, AMPActiPred demonstrates robust predictive capabilities for ABP activity levels with an average PCC of 0.722. Furthermore, AMPActiPred exhibits excellent interpretability, elucidating crucial features associated with antibacterial activity. AMPActiPred is the first computational framework capable of predicting targets and activity levels of ABPs. Finally, to facilitate the utilization of AMPActiPred, we have established a user-friendly web interface deployed at https://awi.cuhk.edu.cn/∼AMPActiPred/.

Antimicrobial therapy based on self-assembling peptides

The emergence of drug-resistant microorganisms has threatened global health, and microbial infections have severely limited the use of medical materials. For example, the attachment and colonization of pathogenic bacteria to medical implant materials can lead to wound infections, inflammation and complications, as well as implant failure, shortening their lifespan and even resulting in patient death. In the era of antibiotic resistance, antimicrobial drug discovery needs to prioritize unconventional therapies that act on new targets or adopt new mechanisms. In this regard, supramolecular antimicrobial peptides have emerged as attractive therapeutic platforms, both as bactericides for combination antibiotics and as delivery vehicles. By taking advantage of their programmable intermolecular and intramolecular interactions, peptides can be modified to form higher-order structures (including nanofibers and nanoparticles) with unique functionality. This paper begins with an analysis of the relationship between peptide self-assembly and antimicrobial activity, describes in detail the research and development of various self-assembled antimicrobial peptides in recent years, and finally explores different combinatorial strategies for self-assembling antimicrobial peptides.

The Antimicrobial Peptide Tilapia Piscidin 4 Induced the Apoptosis of Bladder Cancer Through ERK/SIRT1/PGC-1α Signaling Pathway

Marine antimicrobial peptides have been demonstrated in numerous studies to possess anti-cancer properties. This research investigation aimed to explore the fundamental molecular mechanisms underlying the antitumor activity of Tilapia piscidin 4 (TP4), an antimicrobial peptide, in human bladder cancer. TP4 exhibited a remarkable inhibitory effect on the proliferation of bladder cancer cells through cell cycle arrest at the G2/M phase. Additionally, TP4 upregulated the expression of cleaved caspase-3, caspase-9, and PARP, leading to the activation of apoptotic pathways in bladder cancer cells. TP4 exhibit a marked rise in mitochondria reactive oxygen species, leading to the subsequent loss of potential for the mitochondrial membrane. Furthermore, the inhibition of mitochondrial oxidative phosphorylation resulted in a decrease in downstream ATP production. Meanwhile, TP4-treated bladder cancer cells showed an increase in Bax and ERK but a decrease in SIRT1, PGC-1α, and Bcl2. ERK activation, SIRT1/PGC-1α-axis, and TP4-induced apoptosis were all significantly reversed by the ERK inhibitor SCH772984. Finally, the inhibitory effect of TP4 on tumor growth has been confirmed in a zebrafish bladder cancer xenotransplantation model. These findings suggest that TP4 may be a potential agents for human bladder cancer through apoptosis induction, ERK activation, and the promotion of SIRT1-mediated signaling pathways.

Synthesis and Biological Studies of New Temporin A Analogs Containing Unnatural Amino Acids in Position 7

(1) Background: Antimicrobial resistance is growing at an extreme pace and has proven to be an urgent topic, for research into alternative treatments. Such a prospective possibility is hidden in antimicrobial peptides because of their low to no toxicity, effectiveness at low concentrations, and most importantly their ability to be used for multiple treatments. This work was focused on the study of the effect of the modification in position 7 of Temporin A on its biological activity; (2) Methods: The targeted peptides were synthesized using Fmoc/Ot-Bu SPPS. The antibacterial activity of the analogs was determined using the broth microdilution method and disk-diffusion method. In vitro tests were performed to determine the cytotoxicity, phototoxicity, and antiproliferative activity of the peptide analogs on a panel of tumor and normal cell lines; (3) Results: All analogs except DTCit showed good antibacterial activity, with DTDab having the best activity according to the disk-diffusion method. However, DTCit had an acceptable cytotoxicity, combined with good selectivity against the test MCF-7 cell line; (4) Conclusions: The obtained results revealed the importance of the basicity and length of the side chain at position 7 in the Temporin A sequence for both tested activities.

Insights into Molecular Interactions between a GAPDH-Related Fish Antimicrobial Peptide, Analogs Thereof, and Bacterial Membranes

Interactions between SJGAP (skipjack tuna GAPDH-related antimicrobial peptide) and four analogs thereof with model bacterial membranes were studied using Fourier-transform infrared spectroscopy (FTIR) and molecular dynamics (MD) simulations. MD trajectory analyses showed that the N-terminal segment of the peptide analogs has many contacts with the polar heads of membrane phospholipids, while the central α helix interacts strongly with the hydrophobic core of the membranes. The peptides also had a marked influence on the wave numbers associated with the phase transition of phospholipids organized as liposomes in both the interface and aliphatic chain regions of the infrared spectra, supporting the interactions observed in the MD trajectories. In addition, interesting links were found between peptide interactions with the aliphatic chains of membrane phospholipids, as determined by FTIR and from the MD trajectories, and the membrane permeabilization capacity of these peptide analogs, as previously demonstrated. To summarize, the combined experimental and computational efforts have provided insights into crucial aspects of the interactions between the investigated peptides and bacterial membranes. This work thus makes an original contribution to our understanding of the molecular interactions underlying the antimicrobial activity of these GAPDH-related antimicrobial peptides from Scombridae.

A review on the alternatives to antibiotics and the treatment of antibiotic pollution: Current development and future prospects

Antibiotics, widely used in the fields of medicine, animal husbandry, aquaculture, and agriculture, pose a serious threat to the ecological environment and human health. To prevent antibiotic pollution, efforts have been made in recent years to explore alternative options for antibiotics in animal feed, but the effectiveness of these alternatives in replacing antibiotics is not thoroughly understood due to the variation from case to case. Furthermore, a systematic summary of the specific applications and limitations of antibiotic removal techniques in the environment is crucial for developing effective strategies to address antibiotic contamination. This comprehensive review summarized the current development and potential issues on different types of antibiotic substitutes, such as enzyme preparations, probiotics, and plant extracts. Meanwhile, the existing technologies for antibiotic residue removal were discussed under the scope of application and limitation. The present work aims to highlight the strategy of controlling antibiotics from the source and provide valuable insights for green and efficient antibiotic treatment.

Dermaseptin B2 bioactive gene's potential for anticancer and anti-proliferative effect is linked to the regulation of the BAX/BBC3/AKT pathway

Dermaseptin B2 (DrsB2) is an antimicrobial peptide with anticancer and angiostatic properties. We aimed to assess the in vitro inhibitory effect of pDNA/DrsB2 on the growth of breast cancer cells and its impact on the expression of genes involved in the BAX/BBC3/AKT pathway. The nucleic acid sequence of DrsB2 was artificially synthesized and inserted into the pcDNA3.1( +) Mammalian Expression Plasmid. PCR testing and enzyme digesting procedures evaluated the accuracy of cloning. The vectors were introduced into cells using LipofectamineTM2000 transfection reagent. The breast cancer cells were assessed by flow cytometry, MTT assessment, soft agar colony method, and wound healing investigation. The gene's transcription was evaluated using real-time PCR with a significance level of P < 0.05. The recombinant plasmid harboring the pDNA/DrsB2 vector was effectively produced, and the gene sequence showed absolute homogeneity (100% similarity) with the DrsB2 gene. The transfection effectiveness of MCF-7 and MCF-10A cells was 79% and 68%, respectively. The findings are measured using the growth inhibition 50% (GI50) metric, which indicates the concentration of pDNA/DrsB2 that stops 50% of cell growth. The proportions of early apoptosis, late apoptosis, necrosis, and viable MCF-7 cells in the pDNA/DrsB2 group were 40.50%, 2.31%, 1.69%, and 55.50%, respectively. The results showed a 100% increase in gene expression in programmed cell death following treatment with pDNA/DrsB2 (**P < 0.01). To summarize, the results described in this work offer new possibilities for treating cancer by targeting malignancies via pDNA/DrsB2 and activating the BAX/BBC3/AKT signaling pathways.

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

Determination of Post-Fermentation Waste from Fermented Vegetables as Potential Substitutes for Preservatives in o/w Emulsion

Post-fermentation wastes are rich sources of various biologically active compounds with antimicrobial activity, whose potential is not being fully exploited. One of the possible applications of post-fermentation waste may be its use as a natural preservative that effectively combats pathogens found in formulations. The study aims included the following: (1) compare the antimicrobial and antioxidant activity of fermented vegetable extracts (FVEs), (2) examine the inhibition of cosmetic-borne pathogens by FVEs, and (3) estimate the preservative effectiveness of FVEs in o/w emulsions. It was found that fermented white cabbage, cucumber, celery, and the mixture of fermented white cabbage, cucumber, and celery (1:1:1) showed antibacterial and antifungal activity against all the tested reference microbial strains. The addition of fermented cucumber, celery, and the mixture of fermented white cabbage, cucumber, and celery (1:1:1) to the o/w emulsion fulfilled criterion A of the preservative effectiveness test for S. aureus, E. coli, and A. brasiliensis, but did not fulfill the criterion for P. aeruginosa and C. albicans. The tested FVEs have comparable activity to inhibit pathogens in o/w emulsion as sodium benzoate. The results of our study prove that FVEs can be valuable raw materials supporting the preservative system, which, in turn, can significantly reduce the concentration of preservatives used in o/w emulsion.

Providing insight into the mechanism of action of cationic lipidated oligomers using metabolomics

The increasing resistance of clinically relevant microbes against current commercially available antimicrobials underpins the urgent need for alternative and novel treatment strategies. Cationic lipidated oligomers (CLOs) are innovative alternatives to antimicrobial peptides and have reported antimicrobial potential. An understanding of their antimicrobial mechanism of action is required to rationally design future treatment strategies for CLOs, either in monotherapy or synergistic combinations. In the present study, metabolomics was used to investigate the potential metabolic pathways involved in the mechanisms of antibacterial activity of one CLO, C12-o-(BG-D)-10, which we have previously shown to be effective against methicillin-resistant Staphylococcus aureus (MRSA) ATCC 43300. The metabolomes of MRSA ATCC 43300 at 1, 3, and 6 h following treatment with C12-o-(BG-D)-10 (48 µg/mL, i.e., 3× MIC) were compared to those of the untreated controls. Our findings reveal that the studied CLO, C12-o-(BG-D)-10, disorganized the bacterial membrane as the first step toward its antimicrobial effect, as evidenced by marked perturbations in the bacterial membrane lipids and peptidoglycan biosynthesis observed at early time points, i.e., 1 and 3 h. Central carbon metabolism and the biosynthesis of DNA, RNA, and arginine were also vigorously perturbed, mainly at early time points. Moreover, bacterial cells were under osmotic and oxidative stress across all time points, as evident by perturbations of trehalose biosynthesis and pentose phosphate shunt. Overall, this metabolomics study has, for the first time, revealed that the antimicrobial action of C12-o-(BG-D)-10 may potentially stem from the dysregulation of multiple metabolic pathways.IMPORTANCEAntimicrobial resistance poses a significant challenge to healthcare systems worldwide. Novel anti-infective therapeutics are urgently needed to combat drug-resistant microorganisms. Cationic lipidated oligomers (CLOs) show promise as new antibacterial agents against Gram-positive pathogens like methicillin-resistant Staphylococcus aureus (MRSA). Understanding their molecular mechanism(s) of antimicrobial action may help design synergistic CLO treatments along with monotherapy. Here, we describe the first metabolomics study to investigate the killing mechanism(s) of CLOs against MRSA. The results of our study indicate that the CLO, C12-o-(BG-D)-10, had a notable impact on the biosynthesis and organization of the bacterial cell envelope. C12-o-(BG-D)-10 also inhibits arginine, histidine, central carbon metabolism, and trehalose production, adding to its antibacterial characteristics. This work illuminates the unique mechanism of action of C12-o-(BG-D)-10 and opens an avenue to design innovative antibacterial oligomers/polymers for future clinical applications.

A novel family of defensin-like peptides from Hermetia illucens with antibacterial properties

BACKGROUND

The world faces a major infectious disease challenge. Interest in the discovery, design, or development of antimicrobial peptides (AMPs) as an alternative approach for the treatment of bacterial infections has increased. Insects are a good source of AMPs which are the main effector molecules of their innate immune system. Black Soldier Fly Larvae (BSFL) are being developed for large-scale rearing for food sustainability, waste reduction and as sustainable animal and fish feed. Bioinformatic studies have suggested that BSFL have the largest number of AMPs identified in insects. However, most AMPs identified in BSF have not yet undergone antimicrobial evaluation but are promising leads to treat critical infections.

RESULTS

Jg7197.t1, Jg7902.t1 and Jg7904.t1 were expressed into the haemolymph of larvae following infection with Salmonella enterica serovar Typhimurium and were predicted to be AMPs using the computational tool ampir. The genes encoding these proteins were within 2 distinct clusters in chromosome 1 of the BSF genome. Following removal of signal peptides, predicted structures of the mature proteins were superimposed, highlighting a high degree of structural conservation. The 3 AMPs share primary sequences with proteins that contain a Kunitz-binding domain; characterised for inhibitory action against proteases, and antimicrobial activities. An in vitro antimicrobial screen indicated that heterologously expressed SUMO-Jg7197.t1 and SUMO-Jg7902.t1 did not show activity against 12 bacterial strains. While recombinant SUMO-Jg7904.t1 had antimicrobial activity against a range of Gram-negative and Gram-positive bacteria, including the serious pathogen Pseudomonas aeruginosa.

CONCLUSIONS

We have cloned and purified putative AMPs from BSFL and performed initial in vitro experiments to evaluate their antimicrobial activity. In doing so, we have identified a putative novel defensin-like AMP, Jg7904.t1, encoded in a paralogous gene cluster, with antimicrobial activity against P. aeruginosa.

Investigating the Antimicrobial Effects of a Novel Peptide Derived From Listeriolysin S on S aureus, E coli, and L plantarum: An In Silico and In Vitro Study

Aims

The emergence of antibiotic resistance is one of the most significant issues today. Modifying antimicrobial peptides (AMPs) can improve their effects. In this study, the active region of Listeriolysin S (LLS) as a peptidic toxin has been recognized, and its antibacterial properties have been evaluated by modifying that region.

Methods

After extracting the sequence, the structure of LLS was predicted by PEP-FOLD3. AntiBP and AMPA servers identified its antimicrobial active site. It was modified by adding arginine residue to its 3- and N-terminal regions. Its antimicrobial properties on Staphylococcus aureus, Escherichia coli, and Lactobacillus Plantarum were estimated.

Findings

The results of AntiBP and AntiBP servers demonstrated that a region of 15 amino acids has the most antimicrobial properties (score = 1.696). After adding arginine to the chosen region, the physicochemical evaluation and antimicrobial properties revealed that the designed peptide is a stable AMP with a positive charge of 4, which is not toxic to human erythrocyte cells and has antigenic properties. The results of in vitro and colony counting indicated that at different hours, it caused a significant reduction in the count of S aureus, E coli, and L Plantarum compared with the control sample.

Conclusions

Upcoming research implies that identifying and enhancing the active sites of natural peptides can help combat bacteria.

pH- and Matrix Metalloproteinase-Responsive Multifunctional Bilayer Microneedles Platform for Treatment of Tinea Pedis

Persistent foot odor and itchiness are common symptoms of tinea pedis, significantly disrupting the daily life of those affected. The cuticular barrier at the site of the tinea pedis is thickened, which impedes the effective penetration of antifungal agents. Additionally, fungi can migrate from the skin surface to deeper tissues, posing challenges in the current clinical treatment for tinea pedis. To effectively treat tinea pedis, we developed a platform of bilayer gelatin methacrylate (GelMA) microneedles (MNs) loaded with salicylic acid (SA) and FK13-a1 (SA/FK13-a1@GelMA MNs). SA/FK13-a1@GelMA MNs exhibit pH- and matrix metalloproteinase (MMP)-responsive properties for efficient drug delivery. The MNs are designed to deliver salicylic acid (SA) deep into the stratum corneum, softening the cuticle and creating microchannels. This process enables the antibacterial peptide FK13-a1 to penetrate through the stratum corneum barrier, facilitating intradermal diffusion and exerting antifungal and anti-inflammatory effects. In severe cases of tinea pedis, heightened local pH levels and MMP activity further accelerate drug release. Our research demonstrates that SA/FK13-a1@GelMA MNs are highly effective against Trichophyton mentagrophytes, Trichophyton rubrum, and Candida albicans. They also reduced stratum corneum thickness, fungal burden, and inflammation in a guinea pig model of tinea pedis induced by T. mentagrophytes. Furthermore, it was discovered that SA/FK13-a1@GelMA MNs exhibit excellent biocompatibility. These findings suggest that SA/FK13-a1@GelMA MNs have significant potential for the clinical treatment of tinea pedis as well as other fungal skin disorders.

Metal Cross-Linked Supramolecular Gel Noodles: Structural Insights and Antibacterial Assessment

Achieving precise control over gelator alignment and morphology is crucial for crafting tailored materials and supramolecular structures with distinct properties. We successfully aligned the self-assembled micelles formed by a functionalized dipeptide 2NapFF into long 1-D "gel noodles" by cross-linking with divalent metal chlorides. We identify the most effective cross-linker for alignment, enhancing mechanical stability, and imparting functional properties. Our study shows that Group 2 metal ions are particularly suited for creating mechanically robust yet flexible gel noodles because of their ionic and nondirectional bonding with carboxylate groups. In contrast, the covalent nature and high directional bonds of d-block metal ions with carboxylates tend to disrupt the self-assembly of 2NapFF. Furthermore, the 2NapFF-Cu noodles demonstrated selective antibacterial activity, indicating that the potent antibacterial property of the copper(II) ion is preserved within the cross-linked system. By merging insights into molecular alignment, gel extrusion processing, and integrating specific functionalities, we illustrate how the versatility of dipeptide-based gels can be utilized in creating next-generation soft materials.

Antimicrobial sensitisers: Gatekeepers to avoid the development of multidrug-resistant bacteria

The resistance of multidrug-resistant bacteria to existing antibiotics forces the continued development of new antibiotics and antibacterial agents, but the high costs and long timeframe involved in the development of new agents renders the hope that existing antibiotics may again play a part. The "antibiotic adjuvant" is an indirect antibacterial strategy, but its vague concept has, in the past, limited the development speed of related drugs. In this review article, we put forward an accurate concept of a "non-self-antimicrobial sensitisers (NSAS)", to distinguish it from an "antibiotic adjuvant", and then discuss several scientific methods to restore bacterial sensitivity to antibiotics, and the sources and action mechanism of existing NSAS, in order to guide the development and further research of NSAS.

Expression of molecular markers and synergistic anticancer effects of chemotherapy with antimicrobial peptides on glioblastoma cells

OBJECTIVE

Glioblastoma multiforme (GBM) is the most aggressive and fatal malignant primary brain tumor. The enhancement of the survival rate for glioma patients remains limited, even with the utilization of a combined treatment approach involving surgery, radiotherapy, and chemotherapy. This study was designed to assess the expression of IDH1, TP53, EGFR, Ki-67, GFAP, H3K27M, MGMT, VEGF, NOS, CD99, and ATRX in glioblastoma tissue from 11 patients. We investigated the anticancer impact and combined effects of cathelicidin (LL-37), protegrin-1 (PG-1), with chemotherapy-temozolomide (TMZ), doxorubicin (DOX), carboplatin (CB), cisplatin (CPL), and etoposide (ETO) in primary GBM cells. In addition, we examined the effect of LL-37, PG-1 on normal human fibroblasts and in the C6/Wistar rat intracerebral glioma model.

METHODS

For this study, 11 cases of glioblastoma were evaluated immunohistochemically for IDH1, TP53, EGFR, Ki-67, GFAP, H3K27M, MGMT, VEGF, NOS, CD99, and ATRX. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to study cells viability and to determine cytotoxic effects of LL-37, PG-1 and their combination with chemotherapy in primary GBM cells. Synergism or antagonism was determined using combination index (CI) method. Finally, we established C6 glioblastoma model in Wistar rats to investigate the antitumor activity.

RESULTS

Peptides showed a strong cytotoxic effect on primary GBM cells in the MTT test (IC50 2-16 and 1-32 μM) compared to chemotherapy. The dual-drug combinations of LL-37 + DOX, LL-37 + CB (CI 0.46-0.75) and PG-1 + DOX, PG-1 + CB, PG-1 + TMZ (CI 0.11-0.77), demonstrated a synergism in primary GBM cells. In rat C6 intracerebral GBM model, survival of rats in experimental group (66.75 ± 12.6 days) was prolonged compared with that in control cohort (26.2 ± 2.66 days, p = 0.0008). After LL-37 treatment, experimental group rats showed significantly lower tumor volumes (31.00 ± 8.8 mm3) and weight (49.4 ± 13.3 mg) compared with control group rats (153.8 ± 43.53 mg, p = 0.038; 82.50 ± 7.60 mm3, respectively).

CONCLUSIONS

The combination of antimicrobial peptides and chemical drugs enhances the cytotoxicity of chemotherapy and exerts synergistic antitumor effects in primary GBM cells. Moreover, in vivo study provided the first evidence that LL-37 could effectively inhibit brain tumor growth in rat C6 intracerebral GBM model. These results suggested a significant strategy for proposing a promising therapy for the treatment of GBM.

Effective ciprofloxacin cationic antibacterial agent against persister bacteria with low hemolytic toxicity

With the widespread use of antibiotics, bacterial resistance has developed rapidly. To make matters worse, infections caused by persistent bacteria and biofilms often cannot be completely eliminated, which brings great difficulties to clinical medication. In this work, three series of quinolone pyridinium quaternary ammonium small molecules were designed and synthesized. Most of the compounds showed good antibacterial activity against Gram-positive bacteria (S. aureus and E. faecalis) and Gram-negative bacteria (E. coli and S. maltophilia). The activity of the para-pyridine quaternary ammonium salt was better than that of the meta-pyridine. 3f was the optimal compound with good stability in body fluids and was unlikely to induce bacterial resistance. The hemolysis rate of erythrocytes at 1280 μg/mL for 3f was only 5.1%. Encouragingly, 3f rapidly killed bacteria within 4 h at 4 × MIC concentration and was effective in killing persistent bacteria in biofilms. The antibacterial mechanism experiments showed that 3f could cause disorder of bacterial membrane potential, increase bacterial membrane permeability, dissolve and destroy the membrane. Incomplete bacterial membranes lead to leakage of bacterial genetic material, concomitant production of ROS, and bacterial death due to these multiple effects.

Synergistic Activity of Ingulados Bacteria with Antibiotics against Multidrug-Resistant Pathogens

Antimicrobial resistance is a critical challenge due to the overuse of conventional antimicrobials, and alternative solutions are urgently needed. This study investigates the efficacy of compounds derived from lactic acid bacteria (LAB) fermentation combined with antibiotics against multidrug-resistant pathogens isolated from clinical cases in a hospital setting. Strains of Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecium and faecalis were isolated and selected from blood, respiratory, and urine samples. They were tested against the fermentation products from the Ingulados LAB collection (BAL5, BAL6, BAL8, BAL13, and BAL16), recognized for their antimicrobial efficacy against veterinary pathogens. The activity against multidrug-resistant (MDR) pathogens was evaluated initially, followed by synergy tests using checkerboard assays and subsequent analysis. Bioinformatic assessments and supernatant treatments were performed to characterize the nature of the compounds responsible for the antimicrobial activity. Notably, BAL16 exhibited significant growth inhibition against multidrug-resistant E. faecium. Synergy tests highlighted its combined activity with tetracycline through FICI and surface analysis and bioinformatic analysis unveiled the protein fraction containing bacteriocins as the underlying mechanism. This study highlights BAL16 fermentation products potential as valuable antimicrobial agents against MDR E. faecium infections, attributed to bacteriocins. Further in-depth studies are necessary for complete bacteriocin characterization.

Synthetic Antimicrobial Peptides Fail to Induce Leucocyte Innate Immune Functions but Elicit Opposing Transcriptomic Profiles in European Sea Bass and Gilthead Seabream

Antimicrobial peptides (AMPs) are promising molecules in diverse fields, including aquaculture. AMPs possess lytic effects on a wide range of pathogens, resulting in a potential replacement for traditional antimicrobials in aquaculture. In addition, they also have modulatory effects on host immune responses. Thus, the objective of this work was to evaluate the immunomodulatory capability of three known synthetic AMPs derived from European sea bass, NK-lysin (Nkl), hepcidin (Hamp), and dicentracin (Dic), in head-kidney cell suspensions from European sea bass and gilthead seabream. The tested peptides were neither cytotoxic for European sea bass nor gilthead seabream cells and failed to modulate the respiratory burst and phagocytosis activities. However, they modified the pattern of transcription of immune-related genes differently in both species. Peptides were able to promote the expression of marker genes for anti-inflammatory (il10), antiviral (mx, irf3), cell-mediated cytotoxicity (nccrp1, gzmb), and antibody responses (ighm) in European sea bass, with the Nkl peptide being the most effective. Contrary to this, the effects of those peptides on gilthead seabream mainly resulted in the suppression of immune responses. To conclude, European sea bass-derived peptides can be postulated as potential tools for immunostimulation in European sea bass fish farms, but more efforts are required for their universal use in other species.