Antimicrobial Peptides: Features, Action, and Their Resistance Mechanisms in Bacteria

Antibiotic conjugates: Using molecular Trojan Horses to overcome drug resistance

Antimicrobial resistance (AMR) has become a global health crisis due to the rapid emergence of multi-drug-resistant bacteria. The paucity of novel antibiotics in the clinical pipeline has exacerbated this issue, thereby warranting the development of new antibacterial therapies. The 'Trojan Horse' strategy entails conjugating antibiotics with bioactive components that not only facilitate the entry of antibiotic molecules into bacterial cells by circumventing the membrane barriers, but also augment the effects of conventional antibiotics against recalcitrant pathogens. These Trojan Horse elements can also serve as a promising tool for repurposing drugs with hitherto unexamined antimicrobial activity, or drugs with limited clinical utility due to considerable toxic side effects. In this review, we have discussed the current state of research on antibiotic conjugates with monoclonal antibodies (mAbs), antimicrobial peptides (AMPs) and the iron-chelating siderophores. The rationale and mechanisms of different antibiotic conjugates have been summarized, and the preclinical and clinical evidence pertaining to the activity of these conjugates against drug-resistant pathogens have been reviewed. Furthermore, the challenges associated with the clinical translation of these novel antimicrobials, and the future research directions have also been discussed. While antibiotic conjugates offer an attractive alternative to conventional antimicrobials, there are several obstacles to their clinical translation. A greater understanding of the mechanisms underlying AMR, and continuing advances in genetic engineering, synthetic biology, and bioinformatics will be crucial in designing more selective, potent, and safe antibiotic conjugates for tackling multi-drug resistant (MDR) infections.

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

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

Investigating the Therapeutic Ability of Novel Antimicrobial Peptide Dendropsophin 1 and Its Analogues through Membrane Disruption and Monomeric Pore Formation

Antimicrobial peptides (AMPs) are an alternative source of antibiotics that fight worldwide antibiotic-resistant catastrophes. Dendropsophin 1 (Dc1) is a recently invented novel AMP with 17 amino acid residues obtained from the screen secretion of a frog named Dendropsophus columbianus. Dc1 has two slightly mutated analogues, namely, Dc1.1 and Dc1.2, with improved cationicity and mean amphipathic moment to enhance the selective toxicity against microorganisms. Experimental results indicate that Dc1 and Dc1.1 have similar antimicrobial activity against Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus, whereas the synthesized peptide Dc1.2 has shown antimicrobial activity against a wide range of microorganisms. However, the molecular level details of the peptide-membrane interaction and the corresponding changes in the peptide structure remain elusive. In this study, we investigate the bacterial membrane disruption capability of these AMPs by running a total of 14.2 μs long molecular dynamics (MD) simulations. Our findings suggest that all three peptides affect the upper layer of the membrane with different degrees of disruption. After penetration, Dc1 and Dc1.2 retain stable α-helices in the core region, indicating the potential to disrupt the second layer. However, secondary structure analysis shows that Dc1.2 attains extended helical regions on the C-terminus, suggesting it as the superior candidate among the analogues to have the potential of stable pore formation, leading to bacterial cell death. To speed up our study, we adopt a one-transmembrane configuration of Dc1, Dc1.1, and Dc1.2 and find toroidal pores with subsequent water leakage for Dc1.2.

Amphipathic Antimicrobial Peptides Illuminate a Reciprocal Relationship Between Self-assembly and Cytolytic Activity

Amphipathic character, encoded within the polar sequence patterns of antimicrobial peptides, is a critical structural feature that influences membrane disruptive behavior. Similarly, polar sequence patterns induce self-assembly of amphipathic peptides, which results in the formation of ordered supramolecular structures. The relationship between self-assembly and membrane activity remains an open question of relevance for the development of effective antimicrobial peptides. Here, we report the structural investigation of a class of lytic peptides that self-assemble into filamentous nanomaterials. CryoEM analysis was employed to determine the structure of one of the filaments, which revealed that the peptides are self-assembled into a bilayer nanotube, in which the interaction between layers of amphipathic α-helices was mediated through hydrophobic interactions. The relative stability of the filament peptide assemblies depended on the influence of sequence modifications on the helical conformation. Antimicrobial assays indicated that cytolytic activity was associated with dynamic disassociation of the filamentous assemblies under the assay conditions. Structural modifications of the peptides that stabilized the filaments abrogated lytic activity. These results illuminate a reciprocal relationship between self-assembly and antimicrobial activity in this class of amphipathic peptides and that reversible assembly was critical for the observation of biological activity.

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

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

Oreochromicin-2 shows antimicrobial and immunostimulant effect against respiratory pathogens in pigs

Porcine respiratory diseases have a huge economic impact on pig production. The highest incidence of these diseases is commonly linked to Streptococcus suis, Pasteurella multocida and Bordetella bronchiseptica, some of which are zoonotic posing a risk to human health. The inappropriate and excessive use of conventional antibiotics, as usual procedure for treating respiratory diseases in pigs, has generated the emergence of antimicrobial resistance (AMR), which urgently requires the development of alternative approaches to current antimicrobials. Antimicrobial peptides (AMPs) have rapidly garnered interest as novel therapeutic candidates. Oreochromicin-2 (Oreoch-2), an AMP previously isolated from Oreochromis niloticus gills, has shown broad antibacterial properties against several species. However, studies about its effect on porcine respiratory pathogens and its potential use for the treatment of swine respiratory diseases are not available. In this work we determined the in vitro antimicrobial activity of the peptide against S. suis by a broth microdilution method. Oreoch-2 showed a MIC of 3.13 μM against this pathogen. For in vivo experiments, Yorkshire x Landrace crossbred (LYxL35) weaning pigs aged 30-33 days were allocated in pens containing ten pigs each. To study the influence of the peptide on health status, a total clinical score was determined. The administration of Oreoch-2 improved the clinical behavior of the animals, similar to the conventional antibiotic shotapen, respect to the placebo group. A reduction of bacterial loads in the respiratory tract and lungs was observed in Oreoch-2-treated animals as compared to the placebo group. It was shown that peptide treated-piglets displayed significantly higher serum IgG concentration compared to the control group. These results demonstrated Oreoch-2 potential as an antimicrobial and immunostimulant drug candidate against respiratory diseases in pigs.

Comparative analysis of small secreted peptide signaling during defense response: insights from vascular and non-vascular plants

Small secreted peptides (SSPs) play an important role in modulating immune responses in all land plants. However, the evolution of stress peptide signaling in different plant phyla remains poorly understood. Here, we compared the expression of SSP genes in the pathogen-induced transcriptomes of vascular and non-vascular plants. We found 13, 19, 15, and 28 SSP families that were differentially expressed during infection in Physcomitrium patens, Zea mays, Brassica napus, and Solanum tuberosum, respectively. A comparative study of peptide motifs and predicted three-dimensional structures confirmed the similarity of SSPs across the examined plant species. In both vascular and non-vascular plants. However, only the RALF peptide family was differentially regulated under infection. We also found that EPFL peptides, which are involved in growth and development processes in angiosperms, were differentially regulated in P. patens in response to pathogen infection. The search for novel immune-specific peptides revealed a family of PSY-like peptides that are differentially regulated during infection in P. patens. The treatment with synthetic tyrosine-modified and non-modified PSY, and PSY-like peptides, as well as recombinant EPFL and MEG, validated their roles in the immune response and growth regulation. Thus, our study showed the complex nature of SSP signaling and shed light on the regulation of SSPs in different plant lineages during infection.

Antimicrobial Peptides: Classification, Mechanism, and Application in Plant Disease Resistance

Antimicrobial peptides (AMPs) are a class of alkaline, small molecules found widely in nature. This article surveys the classifications of AMPs, delving into their modes of action and their role in controlling significant plant diseases caused by bacteria, viruses, and fungi. It also explores the prospects and challenges in this field, aiming to provide insights for enhancing crop disease resistance, ensuring food security, deepening the understanding of pathogen mechanisms, and protecting ecological balance.

Distinctive gut antibiotic resistome, potential health risks and underlying pathways upon cerebral ischemia-reperfusion injury

Antibiotic resistance genes (ARGs) as emerging pollutants pose health risks to humans and the environment. Gut microbiota is an important reservoir for ARGs and hotspot for ARG acquisition and dissemination. Non-antibiotic factors (such as disease pathophysiology) affect ARG emergence and dissemination. Cerebral ischemia-reperfusion injury (I/R) commonly occurs in stroke patients. However, effects of I/R on ARG emergence and dissemination are unknown. Therefore, metagenomics was used to unveil selective collection of gut antibiotic resistome and its health risks, key ARG hosts and underlying pathways upon I/R. Changes in gut antibiotic resistome upon I/R were characterized by tetracycline ARG accumulation and decreases in aminoglycoside and glycopeptide ARGs. Besides, changes in gut antibiotic resistome were corrected with those in gut microbiota from phylum to species, serum lipid accumulation and glucose depletion upon I/R. Additionally, health risks of gut microbial multidrug ARGs (such as abem, adek and TolC), macA, aph(3')-I and carO, co-localized with mobile gene elements, were increased upon I/R. Moreover, phyla Firmicutes (especially order Eubacteriales, class Clostridia) and Bacteroidota were key ARG hosts in gut microbiota of I/R gerbils. Furthermore, suppression of vancomycin resistance, and lantibiotic biosynthesis and immunity, disturbances in peptidoglycan biosynthesis and hydrolysis, activation of antimicrobial peptide resistance, lipopolysaccharide biosynthesis, teichoic acid biosynthesis, arabinogalactan biosynthesis, aromatic compound degradation, oxidative phosphorylation, the tricarboxylic acid cycle and its anaplerotic pathways were observed in upon I/R. This study provides novel insights and intervention targets related to selective collection of gut antibiotic resistome and its potential health risks upon I/R.

Application of microfluidic technology and nanoencapsulation to amplify the antibacterial activity of clindamycin against a food born pathogen

Foodborne illnesses are often caused by microbial contamination during preparation or storage. In this work, stable nanoemulsions of clindamycin were prepared using Mentha piperita essential oil (MEO) as a nanocarrier delivery system. Response Surface Methodology was used to optimize the key variables for clindamycin nanoemulsion formulation, including 4.83, 2.83, and 0.14%w/w surfactant, essential oil, and clindamycin, respectively. The stability of MEO/clindamycin nanoemulsion (MEO/C NE) with a mean droplet size of 75.46 ± 3.2 nm was monitored over 3 months. The antibacterial activity of MEO/C NE and bulk compounds against E. coli bacterium was compared using a conventional method and a microfluidic chip. A significant difference in the antibacterial activity was observed by employing a microfluidic chip as compared to the conventional technique, probably due to a high contact surface area between the nanodroplets and bacterial membrane. In the microfluidic chip, the E. coli was completely inhibited in 30 min, whereas 3 h was needed for complete inhibition using the conventional method. The results of this study highlight the significance of nanoemulsion delivery systems to improve the antimicrobial activity of clindamycin and also microfluidic technology as a fast and reliable technique for examining antibiotics and nano delivery systems against microorganisms.

Machine learning and genetic algorithm-guided directed evolution for the development of antimicrobial peptides

INTRODUCTION

Antimicrobial peptides (AMPs) are valuable alternatives to traditional antibiotics, possess a variety of potent biological activities and exhibit immunomodulatory effects that alleviate difficult-to-treat infections. Clarifying the structure-activity relationships of AMPs can direct the synthesis of desirable peptide therapeutics.

OBJECTIVES

In this study, the lipopolysaccharide-binding domain (LBD) was identified through machine learning-guided directed evolution, which acts as a functional domain of the anti-lipopolysaccharide factor family of AMPs identified from Marsupenaeus japonicus.

METHODS

LBDA-D was identified as an output of this algorithm, in which the original LBDMj sequence was the input, and the three-dimensional solution structure of LBDB was determined using nuclear magnetic resonance. Furthermore, our study involved a comprehensive series of experiments, including morphological studies and in vitro and in vivo antibacterial tests.

RESULTS

The NMR solution structure showed that LBDB possesses a circular extended structure with a disulfide crosslink at the terminus and two 310-helices and exhibits a broad antimicrobial spectrum. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that LBDB induced the formation of a cluster of bacteria wrapped in a flexible coating that ruptured and consequently killed the bacteria. Finally, coinjection of LBDB, Vibrio alginolyticus and Staphylococcus aureus in vivo improved the survival of M. japonicus, demonstrating the promising therapeutic role of LBDB for treating infectious disease.

CONCLUSIONS

The findings of this study pave the way for the rational drug design of activity-enhanced peptide antibiotics.

A small antimicrobial peptide derived from a Burkholderia bacterium exhibits a broad-spectrum and high inhibiting activities against crop diseases

Crop diseases cause significant quality and yield losses to global crop products each year and are heavily controlled by chemicals along with very limited antibiotics composed of small molecules. However, these methods often result in environmental pollution and pest resistance, necessitating the development of new bio-controlling products to mitigate these hazards. To identify effective antimicrobial peptides (AMPs) considered as potential sources of future antibiotics, AMPs were screened from five bacterial strains showing antagonism against a representative phytopathogenic fungus (Rhizoctonia Solani) through the Bacillus subtilis expression system, which has been developed for identifying bacterial AMPs by displaying autolysis morphologies. A total of 5000 colonies were screened, and five displaying autolysis morphologies showed antagonism against R. solani. A novel AMP with the strongest antagonism efficiency was determined and tentatively named HR2-7, which is composed of 24 amino acids with an alpha-helical structure. HR2-7 has strong and broad-spectrum antimicrobial activity, tested against 10 g-positive and -negative bacteria and four phytopathogenic fungi by contact culture in plates with minimal lethal concentrations of 4.0 μM. When applied as purified peptide or in fermented B. subtilis culture solution, HR2-7 showed strong controlling efficiency on plants against diverse fungal and bacterial pathogens. Based on current understanding, HR2-7 is recognized as the first AMP derived from an agricultural antagonistic bacterium. It exhibits wide-ranging and notable antimicrobial efficacy, offering a supplementary approach for managing plant diseases, in addition to conventional chemical pesticides and antibiotics.

Identification of a novel antimicrobial peptide from amphioxus ribosomal protein L27

Antimicrobial peptides (AMPs), derived from a variety of proteins such as ribosomal proteins, play a pivotal role in the innate immune system. However, information regarding ribosomal protein-derived AMPs is currently limited and their mechanisms of action remain poorly defined. Here we identified and characterized the antibacterial activity of amphioxus RPL27 (BjRPL27) and its core functional region located at residues 51-72 (termed BjRPL2751-72). We found that BjRPL27 expression was upregulated in the hepatic caecum following bacterial infection. Both the recombinant protein rBjRPL27 and the synthetic peptide BjRPL2751-72 effectively killed the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Aeromonas hydrophila via a combined action of disrupting cell membrane integrity, inducing membrane depolarization, and increasing intracellular reactive oxygen species (ROS) production. Additionally, the sequence of BjRPL2751-72 was highly conserved among all eukaryotic RPL27s, implying an ancient origin for the antibacterial activity of the RPL27 family. In vivo assays showed that BjRPL2751-72 not only efficiently protected zebrafish from A. hydrophila infection, but also killed the bacterium S. aureus on the skin wound of rats. Furthermore, neither BjRPL27 nor BjRPL2751-72 exhibited hemolytic activity towards human red blood cells, making them promising lead molecules for designing novel AMPs. These findings highlight the potential of BjRPL2751-72 as a novel AMP with selective bactericidal properties.

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

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

The novel cathelicidin-DM antimicrobial peptide conjugated carbomer and thermosensitive chitosan hydrogel speeds up wound-healing in both non-infected and S. aureus-infected wounds

The emergence of chronic wound infections and bacterial resistance presents substantial clinical challenges that impact millions worldwide. Antimicrobial peptides (AMPs), recognized for their potent antimicrobial properties, are considered promising alternatives to conventional antibiotics in light of escalating drug resistance. In previous research, we isolated an AMP named cathelicidin-DM from Duttaphrynus melanostictus, which exhibited broad-spectrum efficacy against multidrug-resistant bacteria and demonstrated wound-healing capabilities. This peptide represents a novel therapeutic option for treating infected chronic wounds. However, AMPs are susceptible to degradation when applied in the treatment of wound infections, which may compromise their effectiveness. To further advance the application of cathelicidin-DM in wound healing, we developed cathelicidin-DM-carbomer and thermosensitive cathelicidin-DM-chitosan hydrogels. Our results indicated that cathelicidin-DM interacted with both carbomer and chitosan at the molecular level, adhering to the surface of the hydrogels, which exhibit a three-dimensional network structure and favorable rheological properties. Animal experiments demonstrated that these cathelicidin-DM hydrogels exhibited hemostatic capabilities and significantly enhance the healing of both infected and non-infected full-thickness skin wounds in mice when applied as wound dressings. In summary, cathelicidin-DM carbomer and cathelicidin-DM chitosan hydrogels represent a dual-functional materials with both antimicrobial and wound-healing properties, thereby demonstrating considerable potential for clinical application.

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

Aims

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

Methods

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

Findings

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

Conclusion

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

Differential responses of Bradyrhizobium sp. SUTN9-2 to plant extracts and implications for endophytic interactions within different host plants

Bradyrhizobium sp. strain SUTN9-2 demonstrates cell enlargement, increased DNA content, and efficient nitrogen fixation in response to rice (Oryza sativa) extract. This response is attributed to the interaction between the plant's cationic antimicrobial peptides (CAMPs) and the Bradyrhizobium BacA-like transporter (BclA), similar to bacteroid in legume nodules. The present study reveals that SUTN9-2 can also establish functional endophytic interactions with chili (Capsicum annuum) and tomato (Solanum lycopersicum) plants. When exposed to extracts from chili and tomato, SUTN9-2 exhibits cell elongation, polyploidy, and reduced cell viability, with the effects being less pronounced for tomato extract. Transcriptomic and cytological analyses revealed that genes associated with CAMP resistance, nitrogen metabolism, nitrogen fixation, defense responses, and secretion systems were upregulated, while genes related to the cell cycle and certain CAMP-resistance mechanisms were downregulated, particularly in response to chili extract. This study suggests that SUTN9-2 likely evolves resistance mechanisms against CAMPs found in rice, chili, and tomato plants through mechanisms involving the protease-chaperone DegP, AcrAB-TolC multidrug efflux pumps, and polysaccharides. These mechanisms facilitate efflux, degradation, and the formation of protective barriers to resist CAMPs. Such adaptations enable SUTN9-2 to persist and colonize host plants despite antimicrobial pressures, influencing its viability, cell differentiation, and nitrogen fixation during endophytic interactions with various plant hosts.

Targeted delivery of curcumin and CM11 peptide against hepatocellular carcinoma cells based on binding affinity of PreS1-coated chitosan nanoparticles to SB3 protein

In recent years, the use of cationic peptides as alternative drugs with anticancer activity has received attention. In this study, the targeted release of curcumin (Cur) and CM11 peptide alone and together against hepatocellular carcinoma (HCC) was evaluated using chitosan nanoparticles (CS NPs) coated with Pres1 that target the SB3 antigen of HCC cells (PreS1-Cur-CM11-CS NPs). SB3 protein is the specific antigen of HCC and the PreS1 peptide is a part of the hepatitis B antigen, which can specifically bind to the SB3 protein. Chitosan was used to prepare NPs. To Cur and CM11 loading, drugs were added to the CS solution in appropriate concentrations. Pres1 was coupled to the surface of the NPs using EDC catalyst to target NPs against HepG2 cells. SEM and DLS analysis confirmed that the PreS1-Cur-CM11-CS NPs had a size of about 132 nm, the ideal size for penetrating the cell membrane. The loading of Cur and CM11 was equal to 87% and 65%, respectively, which had a sustained and better release in the acidic environment than in the physiological environment. The MTT assay showed that PreS1-Cur-CM11-CS NPs act in a targeted and specific manner with the highest toxicity on the HepG2 cells compared to the control by a decrease in viability of about 26% after 48 h based on cell apoptosis. The results showed that PreS1-Cur-CM11-CS NPs are capable of targeted and specific drug release against HepG2 cancer cells and have significant potential to fight this cancer.

Hemolymph microbiota and immune effectors' expressions driven by geographical rearing acclimation of the aquacultured Penaeus stylirostris

BACKGROUND

In holobiont, microbiota is known to play a central role on the health and immunity of its host. Then, understanding the microbiota, its dynamic according to the environmental conditions and its link to the immunity would help to react to potential dysbiosis of aquacultured species. While the gut microbiota is highly studied, in marine invertebrates the hemolymph microbiota is often set aside even if it remains an important actor of the hemolymph homeostasis. Indeed, the hemolymph harbors the factors involved in the animal homeostasis that interacts with the microbiota, the immunity. In the Southwest Pacific, the high economical valued shrimp Penaeus stylirostris is reared in two contrasted sites, in New Caledonia (NC) and in French Polynesia (FP).

RESULTS

We characterized the active microbiota inhabiting the hemolymph of shrimps while considering its stability during two seasons and at a one-month interval and evidenced an important microbial variability between the shrimps according to the rearing conditions and the sites. We highlighted specific biomarkers along with a common core microbiota composed of 6 ASVs. Putative microbial functions were mostly associated with bacterial competition, infections and metabolism in NC, while they were highly associated with the cell metabolism in FP suggesting a rearing site discrimination. Differential relative expression of immune effectors measured in the hemolymph of two shrimp populations from NC and FP, exhibited higher level of expression in NC compared to FP. In addition, differential relative expression of immune effectors was correlated to bacterial biomarkers based on their geographical location.

CONCLUSIONS

Our data suggest that, in Pacific shrimps, both the microbiota and the expression of the immune effectors could have undergone differential immunostimulation according to the rearing site as well as a geographical adaptative divergence of the shrimps as an holobiont, to their rearing sites. Further, the identification of proxies such as the core microbiota and site biomarkers, could be used to guide future actions to monitor the bacterial microbiota and thus preserve the productions.

Harnessing Non-Antibiotic Strategies to Counter Multidrug-Resistant Clinical Pathogens with Special Reference to Antimicrobial Peptides and Their Coatings

Antimicrobial resistance is a critical global challenge in the 21st century, validating Sir Alexander Fleming's warning about the misuse of antibiotics leading to resistant microbes. With a dwindling arsenal of effective antibiotics, it is imperative to concentrate on alternative antimicrobial strategies. Previous studies have not comprehensively discussed the advantages and limitations of various strategies, including bacteriophage therapy, probiotics, immunotherapies, photodynamic therapy, essential oils, nanoparticles and antimicrobial peptides (AMPs) within a single review. This review addresses that gap by providing an overview of these various non-antibiotic antimicrobial strategies, highlighting their pros and cons, with a particular emphasis on antimicrobial peptides (AMPs). We explore the mechanism of action of AMPs against bacteria, viruses, fungi and parasites. While these peptides hold significant promise, their application in mainstream drug development is hindered by challenges such as low bioavailability and potential toxicity. However, advancements in peptide engineering and chemical modifications offer solutions to enhance their clinical utility. Additionally, this review presents updates on strategies aimed at improving the cost, stability and selective toxicity of AMPs through the development of peptidomimetics. These molecules have demonstrated effective activity against a broad range of pathogens, making them valuable candidates for integration into surface coatings to prevent device-associated infections. Furthermore, we discuss various approaches for attaching and functionalising these peptides on surfaces. Finally, we recommend comprehensive in vivo studies to evaluate the efficacy of AMPs and their mimetics, investigate their synergistic combinations with other molecules and assess their potential as coatings for medical devices.

sAMP-VGG16: Force-field assisted image-based deep neural network prediction model for short antimicrobial peptides

During the last three decades, antimicrobial peptides (AMPs) have emerged as a promising therapeutic alternative to antibiotics. The approaches for designing AMPs span from experimental trial-and-error methods to synthetic hybrid peptide libraries. To overcome the exceedingly expensive and time-consuming process of designing effective AMPs, many computational and machine-learning tools for AMP prediction have been recently developed. In general, to encode the peptide sequences, featurization relies on approaches based on (a) amino acid (AA) composition, (b) physicochemical properties, (c) sequence similarity, and (d) structural properties. In this work, we present an image-based deep neural network model to predict AMPs, where we are using feature encoding based on Drude polarizable force-field atom types, which can capture the peptide properties more efficiently compared to conventional feature vectors. The proposed prediction model identifies short AMPs (≤30 AA) with promising accuracy and efficiency and can be used as a next-generation screening method for predicting new AMPs. The source code is publicly available at the Figshare server sAMP-VGG16.

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

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

Effective Strategies in Designing Chitosan-hyaluronic Acid Nanocarriers: From Synthesis to Drug Delivery Towards Chemotherapy

The biomedical field faces an ongoing challenge in developing more effective anti-cancer medication due to the significant burden that cancer poses on human health. Extensive research has been conducted on the utilization of natural polysaccharides in nanomedicine owing to their properties of biocompatibility, biodegradability, non-immunogenicity, and non-toxicity. These characteristics make them a potent drug delivery system for cancer therapy. The chitosan hyaluronic acid nanoparticle (CSHANp) system, consisting of chitosan and hyaluronic acid nanoparticles, has exhibited considerable potential as a nanocarrier for various cancer drugs, rendering it one of the most auspicious systems presently accessible. The CSHANps demonstrate remarkable drug loading capacity, precise control over drug release, and exceptional selectivity towards cancer cells. These properties enhance the therapeutic effectiveness against cancerous cells. This article aims to provide a comprehensive analysis of CSHANp, focusing on its characteristics, production techniques, applications, and future prospects.

Innovative Bacterial Therapies and Genetic Engineering Approaches in Colorectal Cancer: A Review of Emerging Strategies and Clinical Implications

Colorectal cancer (CRC) is considered a widespread cancer, ranking second in mortality and incidence among cancer patients worldwide. CRC develops from adenoma to carcinoma through the dynamic interplay of genetic and environmental factors. The conventional modes of treatment, including operation, chemotherapy, and irradiation, are associated with significant challenges, such as drug resistance and toxicity, necessitating the exploration of new treatment modalities. These difficulties reveal the necessity of the emergence of new therapeutic approaches. This review mainly emphasizes the bacterial-based therapies that have recently developed like the engineered bacteriophage therapy and bacterial immunotherapy that pale the existing chemotherapy in terms of toxicity but are effective in killing tumor cells. Also, it also investigates various molecular genetic engineering strategies such as CRISPR-Cas9, CRISPR prime editing and gene silencing to achieve better targeting of CRC. Implementing these new approaches into the forefront of CRC treatment may bring better, more effective therapy with fewer side effects on patients' quality of life.

Identification and characterization of biosynthetic loci of lipooligosaccharide and capsular polysaccharide in Avibacterium paragallinarum

Infectious coryza is an acute respiratory disease in chickens caused by Avibacterium paragallinarum. Lipooligosaccharides (LOSs) and capsular polysaccharides are important components of Av. paragallinarum. Herein, we identified that gene cluster L6 and two genes waaF, waaQ were associated with LOS synthesis, and two genes acbD and ccbF1 were involved in capsular synthesis. Mutant and complementary strains of these genes were generated by natural transformation. Wild-type strains produced LOS that yielded an upper and lower band. In comparison, ΔwaaQ and ΔwaaF yielded a truncated lower band and lacked the upper band, while ΔL6 did not exhibit the upper band, and the lower band was identical to that of the wild-type strain. The survival rates of wild-type strain, ΔwaaF, ΔwaaQ, and ΔL6 in chicken serum were 4.89 % ± 0.27 %, 0.0013 % ± 0.0002 %, 0.43 % ± 0.05 %, and 3.1 % ± 0.35 %, respectively. Notably, the resistances of ΔwaaF, ΔwaaQ, and ΔL6 to chicken serum were significantly lower than that of parent strain. By contrast, the survival rate of the ΔacbD strain was 55.17 % ± 0.61 %, and its resistance to chicken serum was significantly higher than that of the wild-type strain (p < 0.001). Deletion of the waaF, waaQ, L6, acbD, and ccbF1 genes resulted in enhanced formation of biofilm without altering immunogenicity in chickens. The ΔwaaF, ΔwaaQ, and ΔccbF1 strains exhibited heightened susceptibility to fowlicidin-2. Furthermore, ΔwaaF, ΔacbD, and ΔccbF1 strains shown a decrease in pathogenicity (p < 0.05). These results are valuable for advancing research on the pathogenesis of Av. paragallinarum.

Screening and computational characterization of novel antimicrobial cathelicidins from amphibian transcriptomic data

As cold-blooded organisms living in damp and dark environments, amphibians have evolved robust defense mechanisms to protect themselves from predators and infections. Among the wide repertoire of bioactive compounds they produce are antimicrobial peptides (AMPs), which are required as part of innate immunity. One important class of AMPs is cathelicidins, known for their broad-spectrum activity against pathogens and their immunoregulatory roles. However, despite their promising biomedical potential and the increasing availability of omics data, few cathelicidins have been studied in amphibians, mostly through conventional experimental techniques. Here, we present 210 novel cathelicidin sequences from amphibian transcriptomes, identified through a comprehensive computational pipeline, which employed HMMER and BLAST tools to screen cathelicidin domains. These sequences reveal a typical tripartite domain architecture that was confirmed by SignalP and InterProScan analysis. Phylogenetic inference with IQ-TREE classified the sequences into six categories based on evolutionary relationships. Compared to cathelicidins from other vertebrates, amphibian mature peptides exhibit longer average lengths (around 50 amino acids), fewer aromatic and hydrophobic residues, and reduced thermal stability. Furthermore, these amphibian cathelicidins were characterized for their physicochemical and biological properties, revealing significant antimicrobial potential with lower hemolytic capability, especially in anurans, which suggests a balance between their antimicrobial and hemolytic activities predicted through AMPlify, ampir, AmpGram, and HemoPI. Secondary structure estimations, including three-dimensional modeling using AlphaFold2, indicate that amphibian cathelicidins predominantly feature α-helices and coils. Some representative models also display a high α-helix composition with amphipathic topology, facilitating interactions with simulated bacterial membranes as assessed by the PPM approach. Thus, these findings highlight the functional role of cathelicidins in amphibian immunity and their promising biomedical applicability, emphasizing the importance of applying computational methods to expand the scope and reveal the diverse landscape of cathelicidins across vertebrates.

Antimicrobial peptides and proteins against drug-resistant pathogens

The rise of drug-resistant pathogens, driven by the misuse and overuse of antibiotics, has created a formidable challenge for global public health. Antimicrobial peptides and proteins have garnered considerable attention as promising candidates for novel antimicrobial agents. These bioactive molecules, whether derived from natural sources, designed synthetically, or predicted using artificial intelligence, can induce lethal effects on pathogens by targeting key microbial structures or functional components, such as cell membranes, cell walls, biofilms, and intracellular components. Additionally, they may enhance overall immune defenses by modulating innate or adaptive immune responses in the host. Of course, development of antimicrobial peptides and proteins also face some limitations, including high toxicity, lack of selectivity, insufficient stability, and potential immunogenicity. Despite these challenges, they remain a valuable resource in the fight against drug-resistant pathogens. Future research should focus on overcoming these limitations to fully realize the therapeutic potential of antimicrobial peptides in the infection control.

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

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

Unraveling the secrets: Evolution of resistance mediated by membrane proteins

Membrane protein-mediated resistance is a multidisciplinary challenge that spans fields such as medicine, agriculture, and environmental science. Understanding its complexity and devising innovative strategies are crucial for treating diseases like cancer and managing resistant pests in agriculture. This paper explores the dual nature of resistance mechanisms across different organisms: On one hand, animals, bacteria, fungi, plants, and insects exhibit convergent evolution, leading to the development of similar resistance mechanisms. On the other hand, influenced by diverse environmental pressures and structural differences among organisms, they also demonstrate divergent resistance characteristics. Membrane protein-mediated resistance mechanisms are prevalent across animals, bacteria, fungi, plants, and insects, reflecting their shared survival strategies evolved through convergent evolution to address similar survival challenges. However, variations in ecological environments and biological characteristics result in differing responses to resistance. Therefore, examining these differences not only enhances our understanding of adaptive resistance mechanisms but also provides crucial theoretical support and insights for addressing drug resistance and advancing pharmaceutical development.

Characterization of Structural Properties and Antimicrobial Activity of the C3f Peptide of Complement System

The C3f peptide is a by-product of regulation of the activated complement system with no firmly established function of its own. We have previously shown that C3f exhibits moderate antimicrobial activity against some Gram-positive bacteria in vitro. Presence of two histidine residues in the amino acid sequence of the peptide suggests enhancement of its antimicrobial activity at lower pH and in the presence of metal cations, particularly zinc cations. Since such conditions could be realized in inflammatory foci, the study of dependence of C3f activity on pH and presence of metal cations could provide an opportunity to assess biological significance of antimicrobial properties of the peptide. The peptide C3f and its analogs with histidine residues substituted by lysines or serines, C3f[H/K] and C3f[H/S], were prepared by solid-phase synthesis. Using CD spectroscopy, we found that C3f contained a β-hairpin and unstructured regions; presence of Zn2+ did not affect conformation of the peptide. In the present work, it was shown that C3f could also exhibit antimicrobial activity against Gram-negative bacteria, in particular, Pseudomonas aeruginosa ATCC 27583. Exposure of P. aeruginosa and Listeria monocytogenes EGD to the peptide was accompanied by disruption of the barrier function of bacterial membranes. Zn2+ ions, unlike Cu2+ ions, enhanced antimicrobial activity of C3f against L. monocytogenes, with 4- and 8-fold molar excess of Zn2+ being no more effective than a 20% excess. Activity of the C3f analogs was also enhanced to some extent by the zinc ions. Thus, we hypothesize existence of the histidine-independent formation of C3f-Zn2+ complexes leading to increase in the total charge and antimicrobial activity of the peptide. In the presence of 0.15 M NaCl, C3f lost its antimicrobial activity regardless of the presence of Zn2+, indicating an insignificant role of C3f as an endogenous antimicrobial peptide. Presence of C3f eliminated bactericidal effect of Zn2+ against the zinc-sensitive Escherichia coli strain ESBL 521/17, indirectly confirming interaction of the peptide with Zn2+. Activity of C3f against Micrococcus luteus A270 increased with decreasing pH, while effect of pH on the C3f activity against L. monocytogenesis was more complex. In this work, we show significance of the factors such as pH and metal cations in realization of antimicrobial activity of peptides based on the example of C3f.

An escape from ESKAPE pathogens: A comprehensive review on current and emerging therapeutics against antibiotic resistance

The rise of antimicrobial resistance has positioned ESKAPE pathogens as a serious global health threat, primarily due to the limitations and frequent failures of current treatment options. This growing risk has spurred the scientific community to seek innovative antibiotic therapies and improved oversight strategies. This review aims to provide a comprehensive overview of the origins and resistance mechanisms of ESKAPE pathogens, while also exploring next-generation treatment strategies for these infections. In addition, it will address both traditional and novel approaches to combating antibiotic resistance, offering insights into potential new therapeutic avenues. Emerging research underscores the urgency of developing new antimicrobial agents and strategies to overcome resistance, highlighting the need for novel drug classes and combination therapies. Advances in genomic technologies and a deeper understanding of microbial pathogenesis are crucial in identifying effective treatments. Integrating precision medicine and personalized approaches could enhance therapeutic efficacy. The review also emphasizes the importance of global collaboration in surveillance and stewardship, as well as policy reforms, enhanced diagnostic tools, and public awareness initiatives, to address resistance on a worldwide scale.

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.

In-silico and in-vitro study of novel antimicrobial peptide AM1 from Aegle marmelos against drug-resistant Staphylococcus aureus

Antimicrobial peptides have garnered increasing attention as potential alternatives due to their broad-spectrum antimicrobial activity and low propensity for developing resistance. This is for the first time; proteome sequences of Aegle marmelos were subjected to in-silico digestion and AMP prediction were performed using DBAASP server. After screening the peptides on the basis of different physiochemical property, peptide sequence GKEAATKAIKEWGQPKSKITH (AM1) shows the maximum binding affinity with - 10.2 Kcal/mol in comparison with the standard drug (Trimethoprim) with - 7.4 kcal/mol and - 6.8 Kcal/mol for DHFR and SaTrmK enzyme respectively. Molecular dynamics simulation performed for 300ns, it has been found that peptide was able to stabilize the protein more effectively, analysed by RMSD, RMSF, and other statistical analysis. Free binding energy for DHFR and SaTrmK interaction from MMPBSA analysis with peptide was found to be -47.69 and - 44.32 Kcal/mol and for Trimethoprim to be -13.85 Kcal/mol and - 11.67 Kcal/mol respectively. Further in-vitro study was performed against Methicillin Susceptible Staphylococcus aureus (MSSA), Methicillin Resistant Staphylococcus aureus (MRSA), Multi-Drug Resistant Staphylococcus aureus (MDR-SA) strain, where MIC values found to be 2, 4, and 8.5 µg/ml lesser in comparison to trimethoprim which has higher MIC values 2.5, 5, and 9.5 µg/ml respectively. Thus, our study provides the insight for the further in-vivo study of the peptides against multi-drug resistant S. aureus.

Development of Phloroglucinol-Linked Tris-Quaternary Ammonium Salt Antimicrobial Peptide Mimics with Low Cytotoxicity and Broad-Spectrum Antibacterial Activity

Encouraged by the significantly different toxicities and antibacterial activities of diverse linkers, such as alkyl and aromatic nuclei linkers, and the unique structure of phloroglucinol, we synthesized a series of tris-quaternary ammonium salt (tris-QAS) antibacterial peptide mimics based on the marketed drug phloroglucinol. Among them, 2f displayed excellent activity against Staphylococcus aureus (MIC = 0.5 μg/mL) and high selectivity (SI > 2560). Surprisingly, the cytotoxicity of 2f (CC50 = 152.7 μg/mL) was dramatically better than those of alkyl QAS I and hydroquinone QAS II. Additionally, 2f possessed rapid bactericidal capability, was not prone to inducing bacterial resistance, and also exhibited excellent activity against S. aureus biofilms and persistent bacteria. Mechanistic research and transcriptome analysis revealed that 2f can interfere with the normal metabolism of bacterial cells, and it can specifically bind with phosphatidylglycerol to destroy the cell membrane. Importantly, 2f exhibited potent in vivo antibacterial activity in a mouse subcutaneous methicillin-resistant S. aureus (MRSA) infection model.

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

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

Peptide-Membrane Docking and Molecular Dynamic Simulation of In Silico Detected Antimicrobial Peptides from Portulaca oleracea's Transcriptome

The main issue with clinical infections is multidrug resistance to traditional antibiotics. As they are essential to innate immunity, shielding hosts from pathogenic microbes, traditional herbal remedies are an excellent supplier of antimicrobial peptides (AMPs), vital parts of defensive systems. Nevertheless, little is known about the bioactive peptide components of most ethnobotanical species. Our goal in this study was to find new, likely AMPs from Portulaca oleracea (P. oleracea) using in silico studies. The P. oleracea transcriptome was gained from Sequence Read Archive (SRA) and quality controlled, then adapters and other low-quality reads were trimmed. Afterward, de novo assembled and translated open reading frames (ORFs) were determined. Next, the ORFs were filtered based on AMP physiochemical criteria and deep learning methods. Finally, the five selected putative AMPs docked with E. coli and S. aureus membranes that showed penetration in bilayers. In this step, PO2 was chosen as a candidate AMP to analyze with molecular dynamics (MD) simulations. Our data demonstrated that PO2 is more stable in E. coli than in S. aureus. Moreover, these predicted AMPs can be good candidates for in vitro and in vivo analysis.

The role of cathelicidins in neutrophil biology

Despite their relatively short lifespan, neutrophils are tasked with counteracting pathogens through various functions, including phagocytosis, production of reactive oxygen species, neutrophil extracellular traps (NETs), and host defense peptides. Regarding the latter, small cationic cathelicidins present a conundrum in neutrophil function. Although primarily recognized as microbicides with an ability to provoke pores in microbial cell walls, the ability of cathelicidin to modulate key neutrophil functions is also of great importance, including the release of chemoattractants, cytokines, and reactive oxygen species, plus prolonging neutrophil lifespan. Cumulative evidence indicates a less recognized role of cathelicidin as an "immunomodulator"; however, this term is not always explicit, and its relevance in neutrophil responses during infection and inflammation is seldom discussed. This review compiles and discusses studies of how neutrophils use cathelicidin to respond to infections, while also acknowledging immunomodulatory aspects of cathelicidin through potential crosstalk between sources of the peptide.

Immune function of a C-type lectin with long tandem repeats and abundant threonine in the ridgetail white prawn Exopalaemon carinicauda

C-type lectins (CTLs) are an important class of pattern recognition receptors (PRRs) that exhibit structural and functional diversity in invertebrates. Repetitive DNA sequences are ubiquitous in eukaryotic genomes, representing distinct modes of genome evolution and promoting new gene generation. Our study revealed a new CTL that is composed of two long tandem repeats, abundant threonine, and one carbohydrate recognition domain (CRD) in Exopalaemon carinicauda and has been designated EcTR-CTL. The full-length cDNA of EcTR-CTL was 1242 bp long and had an open reading frame (ORF) of 999 bp that encoded a protein of 332 amino acids. The genome structure of EcTR-CTL contains 4 exons and 3 introns. The length of each repeat unit in EcTR-CTL was 198 bp, which is different from the short tandem repeats reported previously in prawns and crayfish. EcTR-CTL was abundantly expressed in the intestine and hemocytes. After Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenge, the expression level of EcTR-CTL in the intestine was upregulated. Knockdown of EcTR-CTL downregulated the expression of anti-lipopolysaccharide factor, crustin, and lysozyme during Vibrio infection. The recombinant CRD of EcTR-CTL (rCRD) could bind to bacteria, lipopolysaccharides, and peptidoglycans. Additionally, rCRD can directly bind to WSSV. These findings indicate that 1) CTLs with tandem repeats may be ubiquitous in crustaceans, 2) EcTR-CTL may act as a PRR to participate in the innate immune defense against bacteria via nonself-recognition and antimicrobial peptide regulation, and 3) EcTR-CTL may play a positive or negative role in the process of WSSV infection by capturing virions.

Antimicrobial peptide-fibrin glue mixture for treatment of methicillin-resistant Staphylococcus aureus-infected wounds

Aim: This study was conducted to investigate the effect of fibrin glue-CM11 antibacterial peptide mixture (FG-P) on the healing of infected wounds in vivo.Materials & methods: We formulated a mixture of FG-P and evaluated its antimicrobial activity in vitro against multidrug-resistant (MDR) bacteria involved in wound infection as well as its healing effect on wound infected by methicillin-resistant S. aureus (MRSA) in vivo.Results: The peptide had an MIC of 8 μg/ml against all bacteria isolates. Growth inhibition zones were evident for FG-P compared with FG. The in vivo study showed that the FG-P could be significantly effective in healing the MRSA-infected wound.Conclusion: The use of FG-P mixture is a very suitable option for treating infected wounds.

Nanoparticle-Based Strategies for Managing Biofilm Infections in Wounds: A Comprehensive Review

Chronic wounds containing opportunistic bacterial pathogens are a growing problem, as they are the primary cause of morbidity and mortality in developing and developed nations. Bacteria can adhere to almost every surface, forming architecturally complex communities called biofilms that are tolerant to an individual's immune response and traditional treatments. Wound dressings are a primary source and potential treatment avenue for biofilm infections, and research has recently focused on using nanoparticles with antimicrobial activity for infection control. This Review categorizes nanoparticle-based approaches into four main types, each leveraging unique mechanisms against biofilms. Metallic nanoparticles, such as silver and copper, show promising data due to their ability to disrupt bacterial cell membranes and induce oxidative stress, although their effectiveness can vary based on particle size and composition. Phototherapy-based nanoparticles, utilizing either photodynamic or photothermal therapy, offer targeted microbial destruction by generating reactive oxygen species or localized heat, respectively. However, their efficacy depends on the presence of light and oxygen, potentially limiting their use in deeper or more shielded biofilms. Nanoparticles designed to disrupt extracellular polymeric substances directly target the biofilm structure, enhancing the penetration and efficacy of antimicrobial agents. Lastly, nanoparticles that induce biofilm dispersion represent a novel strategy, aiming to weaken the biofilm's defense and restore susceptibility to antimicrobials. While each method has its advantages, the selection of an appropriate nanoparticle-based treatment depends on the specific requirements of the wound environment and the type of biofilm involved. The integration of these nanoparticles into wound dressings not only promises enhanced treatment outcomes but also offers a reduction in the overall use of antibiotics, aligning with the urgent need for innovative solutions in the fight against antibiotic-tolerant infections. The overarching objective of employing these diverse nanoparticle strategies is to replace antibiotics or substantially reduce their required dosages, providing promising avenues for biofilm infection management.

The antiherpetic and anti-inflammatory activity of the frog-derived peptide Hylin-a1

AIM

The high incidence of virus-related infections and the large diffusion of drug-resistant pathogens stimulate the search and identification of new antiviral agents with a broad spectrum of action. Antivirals can be designed to act on a single target by interfering with a specific step in the viral lifecycle. On the contrary, antiviral peptides (AVPs) are known for acting on a wide range of viruses, with a diversified mechanism of action targeting virus and/or host cell. In the present study, we evaluated the antiviral potential of the peptide Hylin-a1 secreted by the frog Hypsiobas albopunctatus against members of the Herpesviridae family.

METHODS AND RESULTS

The inhibitory capacity of the peptide was evaluated in vitro by plaque assays in order to understand the possible mechanism of action. The results were also confirmed by real-time PCR and Western blot evaluating the expression of viral genes. Hylin-a1 acts to block the herpetic infection interfering at the early stages of both herpes simplex virus type 1 (HSV-1) and type 2 infection. Its mechanism is mainly directed on the membrane, probably by damaging the viral envelope. The same effect was also observed against HSV-1 strains resistant to acyclovir.

CONCLUSIONS

The data presented in this study, such as the increased activity of the peptide when combined to acyclovir, a weak hemolytic profile, an anti-inflammatory effect, and a tolerable half-life in serum, indicates Hylin-a1 as a novel antiherpetic molecule with promising potential in the clinical setting.

Antibacterial efficacy and membrane mechanism of action of the Serratia-derived non-ionic lipopeptide, serrawettin W2-FL10

The study aimed to investigate the antibacterial activity, cytotoxicity, and mechanism of action of the non-ionic, cyclic lipopeptide, serrawettin W2-FL10 against Staphylococcus aureus. W2-FL10 exhibited potent activity against the Gram-positive bacteria S. aureus, Enterococcus faecalis, Enterococcus faecium, Listeria monocytogenes, and Bacillus subtilis, with minimum inhibitory concentration (MIC) values ranging from 6.3 to 31.3 μg/mL, while no activity was observed against Gram-negative bacteria. Broth microdilution assays showed that W2-FL10 interacted with key cell membrane components, such as lipid phosphatidyl glycerol and lipoteichoic acid of S. aureus. Upon membrane interaction, W2-FL10 dissipated membrane potential within 12 min and increased S. aureus membrane permeability within 28-40 min, albeit at slower rates and higher concentrations than the lytic peptide melittin. The observed membrane permeability, as detected with propidium iodide (PI), may be attributed to transmembrane pores/lesions, possibly dependent on dimer-driven lipopeptide oligomerization in the membrane. Scanning electron microscopy (SEM) imaging also visually confirmed the formation of lesions in the cell wall of one of the S. aureus strains, and cell damage within 1 h of exposure to W2-FL10, corroborating the rapid time-kill kinetics of the S. aureus strains. This bactericidal action against the S. aureus strains corresponded to membrane permeabilization by W2-FL10, indicating that self-promoted uptake into the cytosol may be part of the mode of action. Finally, this lipopeptide exhibited low to moderate cytotoxicity to the Chinese hamster ovarian (CHO) cell line in comparison to the control (emetine) with an optimal lipophilicity range (log D value of 2.5), signifying its potential as an antibiotic candidate.

IMPORTANCE

Antimicrobial resistance is a major public health concern, urgently requiring antibacterial compounds exhibiting low adverse health effects. In this study, a novel antibacterial lipopeptide analog is described, serrawettin W2-FL10 (derived from Serratia marcescens), with potent activity displayed against Staphylococcus aureus. Mechanistic studies revealed that W2-FL10 targets the cell membrane of S. aureus, causing depolarization and permeabilization because of transmembrane lesions/pores, resulting in the leakage of intracellular components, possible cytosolic uptake of W2-FL10, and ultimately cell death. This study provides the first insight into the mode of action of a non-ionic lipopeptide. The low to moderate cytotoxicity of W2-FL10 also highlights its application as a promising therapeutic agent for the treatment of bacterial infections.

Insect meal in aquafeeds: A sustainable path to enhanced mucosal immunity in fish

The mucosal surfaces of fish, including their intestines, gills, and skin, are constantly exposed to various environmental threats, such as water quality fluctuations, pollutants, and pathogens. However, various cells and microbiota closely associated with these surfaces work in tandem to create a functional protective barrier against these conditions. Recent research has shown that incorporating specific feed ingredients into fish diets can significantly boost their mucosal and general immune response. Among the various ingredients being investigated, insect meal has emerged as one of the most promising options, owing to its high protein content and immunomodulatory properties. By positively influencing the structure and function of mucosal surfaces, insect meal (IM) has the potential to enhance the overall immune status of fish. This review provides a comprehensive overview of the potential benefits of incorporating IM into aquafeed as a feed ingredient for augmenting the mucosal immune response of fish.

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.

Sensitivity to antimicrobial peptide A (SapA) contributes to the survival of Salmonella typhimurium against antimicrobial peptides, neutrophils and virulence in mice

Host-generated antimicrobial peptides (AMPs) play a pivotal role in defense against bacterial pathogens. AMPs kill invading bacteria majorly by disrupting the bacterial cell walls. AMPs are actively synthesized and released into the lumen of the gastrointestinal tract to limit colonization of enteric pathogens like Salmonella typhimurium (S. typhimurium). However, S. typhimurium has evolved several resistance mechanisms to defend AMPs. The multicomponent SapABCDF uptake transporter is one such system that helps in resisting AMPs. In the current study, we analyzed the role of S. typhimurium SapA against stress survival and virulence of this bacterium. ∆sapA mutant strain showed hypersensitivity to AMPs, like melittin and mastoparan. Further, ∆sapA mutant showed more than 22 folds (p = 0.019) hypersensitivity to neutrophils as compared to the WT strain of S. typhimurium. In addition, ∆sapA strain showed defective survival in mice. In conclusion, the results of the current study suggest that the SapA is essential for survival against AMPs and virulence of S. typhimurium.

Mechanistic Study of Antimicrobial Effectiveness of Cyclic Amphipathic Peptide [R4W4] against Methicillin-Resistant Staphylococcus aureus Clinical Isolates

Antimicrobial peptides (AMPs) are being explored as a potential strategy to combat antibiotic resistance due to their ability to reduce susceptibility to antibiotics. This study explored whether the [R4W4] peptide mode of action is bacteriostatic or bactericidal using modified two-fold serial dilution and evaluating the synergism between gentamicin and [R4W4] against Escherichia coli (E. coli) and methicillin-resistant Staphylococcus aureus (MRSA) by a checkered board assay. [R4W4] exhibited bactericidal activity against bacterial isolates (MBC/MIC ≤ 4), with a synergistic effect with gentamicin against E. coli (FICI = 0.3) but not against MRSA (FICI = 0.75). Moreover, we investigated the mechanism of action of [R4W4] against MRSA by applying biophysical assays to evaluate zeta potential, cytoplasmic membrane depolarization, and lipoteichoic acid (LTA) binding affinity. [R4W4] at a 16 mg/mL concentration stabilized the zeta potential of MRSA -31 ± 0.88 mV to -8.37 mV. Also, [R4W4] at 2 × MIC and 16 × MIC revealed a membrane perturbation process associated with concentration-dependent effects. Lastly, in the presence of BODIPY-TR-cadaverine (BC) fluorescence dyes, [R4W4] exhibited binding affinity to LTA comparable with melittin, the positive control. In addition, the antibacterial activity of [R4W4] against MRSA remained unchanged in the absence and presence of LTA, with an MIC of 8 µg/mL. Therefore, the [R4W4] mechanism of action is deemed bactericidal, involving interaction with bacterial cell membranes, causing concentration-dependent membrane perturbation. Additionally, after 30 serial passages, there was a modest increment of MRSA strains resistant to [R4W4] and a change in antibacterial effectiveness MIC [R4W4] and vancomycin by 8 and 4 folds with a slight change in Levofloxacin MIC 1 to 2 µg/mL. These data suggest that [R4W4] warrants further consideration as a potential AMP.

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.

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/.

Molecular characterization, expression and antibacterial function of a macin, HdMac, from Haliotis discus hannai

Macins are a family of antimicrobial peptides, which play multiple roles in the elimination of invading pathogens. In the present study, a macin was cloned and characterized from Pacific abalone Haliotis discus hannai (Designated as HdMac). Analysis of the conserved domain suggested that HdMac was a new member of the macin family. In non-stimulated abalones, HdMac transcripts were constitutively expressed in all five tested tissues, especially in hemocytes. After Vibrio harveyi stimulation, the expression of HdMac mRNA in hemocytes was significantly up-regulated at 12 hr (P < 0.01). RNAi-mediated knockdown of HdMac transcripts affected the survival rates of abalone against V. harveyi. Moreover, recombinant protein of HdMac (rHdMac) exhibited high antibacterial activities against invading bacteria, especially for Vibrio anguillarum. In addition, rHdMac possessed binding activities towards glucan, lipopolysaccharides (LPS), and peptidoglycan (PGN), but not chitin in vitro. Membrane integrity analysis revealed that rHdMac could increase the membrane permeability of bacteria. Meanwhile, both the phagocytosis and chemotaxis ability of hemocytes could be significantly enhanced by rHdMac. Overall, the results showed that HdMac could function as a versatile molecule involved in immune responses of H. discus hannai.