Insect Antimicrobial Peptides, a Mini Review

Melittin-The principal toxin of honeybee venom-Is also produced in the honeybee fat body

Melittin is a powerful toxin present in honeybee venom that is active in a wide range of animals, from insects to humans. Melittin exerts numerous biological, toxicological, and pharmacological effects, the most important of which is destruction of the cell membrane. The phospholipase activity of melittin and its ability to activate phospholipases in the venom contribute to these actions. Using analytical methods, we discovered that the honeybee Apis mellifera produces melittin not only in the venom gland but also in its fat body cells, which remain resistant to this toxin's effects. We suggest that melittin acts as an anti-bacterial agent, since its gene expression is significantly upregulated when honeybees are infected with Escherichia coli and Listeria monocytogenes bacteria; additionally, melittin effectively kills these bacteria in the disc diffusion test. We hypothesize that the chemical and physicochemical properties of the melittin molecule (hydrophilicity, lipophilicity, and capacity to form tetramers) in combination with reactive conditions (melittin concentration, salt concentration, pH, and temperature) are responsible for the targeted destruction of bacterial cells and apparent tolerance towards own tissue cells. Considering that melittin is an important current and, importantly, potential broad-spectrum medication, a thorough understanding of the observed phenomena may significantly increase its use in clinical practice.

Expression of honey bee (Apis mellifera) sterol homeostasis genes in food jelly producing glands of workers

Adult workers of Western honey bees (Apis mellifera L.) acquire sterols from their pollen diet. These food sterols are transported by the hemolymph to peripheral tissues such as the mandibular and the hypopharyngeal glands in the worker bees' heads that secrete food jelly which is fed to developing larvae. As sterols are obligatory components of biological membranes and essential precursors for molting hormone synthesis in insects, they are indispensable to normal larval development. Thus, the study of sterol delivery to larvae is important for a full understanding of honey bee larval nutrition and development. Whereas hypopharyngeal glands only require sterols for their membrane integrity, mandibular glands add sterols, primarily 24-methylenecholesterol, to its secretion. For this, sterols must be transported through the glandular epithelial cells. We have analyzed for the first time in A. mellifera the expression of genes which are involved in intracellular movement of sterols. Mandibular and hypopharyngeal glands were dissected from newly emerged bees, 6-day-old nurse bees that feed larvae and 26-day-old forager bees. The expression of seven genes involved in intracellular sterol metabolism was measured with quantitative real-time PCR. Relative transcript abundance of sterol metabolism genes was significantly influenced by the age of workers and specific genes but not by gland type. Newly emerged bees had significantly more transcripts for six out of seven genes than older bees indicating that the bulk of the proteins needed for sterol metabolism are produced directly after emergence.

The distinctive effect of different insect powders as meat extenders in beef burgers subjected to cooking and in vitro gastrointestinal digestion

Mealworm (MWP), migratory locust (LP), and house cricket (CP) are novel foods recently authorized by the European Commission. This work tested their powders as meat extenders at 5% inclusion in beef burgers. Insect powders were abundant in phenolics, recording the highest values in LP (1184.9 μg/g). The sensory analysis highlighted a higher visual and olfactory acceptability for MWP-burgers, followed by CP- and LP-burgers, whereas the texture of cooked burgers remained unaffected. Following pan-cooking, MWP-burgers and control exhibited comparable chemical profiles, while a significant down-accumulation of the heterocyclic amine 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline was observed in CP-burgers. In vitro gastrointestinal digestion highlighted metabolomic trends like control for MWP- and LP-burgers. In contrast, a reduced accumulation of lipids and increased content of dipeptides like glutaminylarginine (possibly acting as enzyme modulators) was observed for the CP-burgers.

Royal Jelly: Biological Action and Health Benefits

Royal jelly (RJ) is a highly nutritious natural product with great potential for use in medicine, cosmetics, and as a health-promoting food. This bee product is a mixture of important compounds, such as proteins, vitamins, lipids, minerals, hormones, neurotransmitters, flavonoids, and polyphenols, that underlie the remarkable biological and therapeutic activities of RJ. Various bioactive molecules like 10-hydroxy-2-decenoic acid (10-HDA), antibacterial protein, apisin, the major royal jelly proteins, and specific peptides such as apisimin, royalisin, royalactin, apidaecin, defensin-1, and jelleins are characteristic ingredients of RJ. RJ shows numerous physiological and pharmacological properties, including vasodilatory, hypotensive, antihypercholesterolaemic, antidiabetic, immunomodulatory, anti-inflammatory, antioxidant, anti-aging, neuroprotective, antimicrobial, estrogenic, anti-allergic, anti-osteoporotic, and anti-tumor effects. Moreover, RJ may reduce menopause symptoms and improve the health of the reproductive system, liver, and kidneys, and promote wound healing. This article provides an overview of the molecular mechanisms underlying the beneficial effects of RJ in various diseases, aging, and aging-related complications, with special emphasis on the bioactive components of RJ and their health-promoting properties. The data presented should be an incentive for future clinical studies that hopefully will advance our knowledge about the therapeutic potential of RJ and facilitate the development of novel RJ-based therapeutic opportunities for improving human health and well-being.

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.

Cereal weevils' antimicrobial peptides: at the crosstalk between development, endosymbiosis and immune response

Interactions between animals and microbes are ubiquitous in nature and strongly impact animal physiology. These interactions are shaped by the host immune system, which responds to infections and contributes to tailor the associations with beneficial microorganisms. In many insects, beneficial symbiotic associations not only include gut commensals, but also intracellular bacteria, or endosymbionts. Endosymbionts are housed within specialized host cells, the bacteriocytes, and are transmitted vertically across host generations. Host-endosymbiont co-evolution shapes the endosymbiont genome and host immune system, which not only fights against microbial intruders, but also ensures the preservation of endosymbionts and the control of their load and location. The cereal weevil Sitophilus spp. is a remarkable model in which to study the evolutionary adaptation of the immune system to endosymbiosis owing to its binary association with a unique, relatively recently acquired nutritional endosymbiont, Sodalis pierantonius. This Gram-negative bacterium has not experienced the genome size shrinkage observed in long-term endosymbioses and has retained immunogenicity. We focus here on the sixteen antimicrobial peptides (AMPs) identified in the Sitophilus oryzae genome and their expression patterns in different tissues, along host development or upon immune challenges, to address their potential functions in the defensive response and endosymbiosis homeostasis along the insect life cycle. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Immune Gene Repertoire of Soft Scale Insects (Hemiptera: Coccidae)

Insects possess an effective immune system, which has been extensively characterized in several model species, revealing a plethora of conserved genes involved in recognition, signaling, and responses to pathogens and parasites. However, some taxonomic groups, characterized by peculiar trophic niches, such as plant-sap feeders, which are often important pests of crops and forestry ecosystems, have been largely overlooked regarding their immune gene repertoire. Here we annotated the immune genes of soft scale insects (Hemiptera: Coccidae) for which omics data are publicly available. By using immune genes of aphids and Drosophila to query the genome of Ericerus pela, as well as the transcriptomes of Ceroplastes cirripediformis and Coccus sp., we highlight the lack of peptidoglycan recognition proteins, galectins, thaumatins, and antimicrobial peptides in Coccidae. This work contributes to expanding our knowledge about the evolutionary trajectories of immune genes and offers a list of promising candidates for developing new control strategies based on the suppression of pests' immunity through RNAi technologies.

A novel defensin-like peptide C-13326 possesses protective effect against multidrug-resistant Aeromonas schubertii in hybrid snakehead (Channa maculate ♀ × Channa argus ♂)

The purpose of this study was to investigate whether a defensin-like antimicrobial peptide (C-13326 peptide) identified in Hermetia illucens could possess protective effect against multidrug-resistant Aeromonas schubertii in hybrid snakehead (Channa maculate ♀ × Channa argus ♂). The cDNA of C-13326 peptide comprised 243 nucleotides encoding 80 amino acids, with six conserved cysteine residues and the classical CSαβ structure. The recombinant expression plasmid pPIC9K-C-13326 was constructed and transformed into GS115 Pichia pastoris, and the C-13326 peptide was expressed by induction with 1% methanol. The crude extract of C-13326 peptide was precipitated by ammonium sulfate, assayed by Braford method, detected by tricine-SDS-PAGE, evaluated by BandScan software and identified by liquid chromatography-mass spectrometry. The C-13326 peptide was shown to have inhibitory activity against the growth of multidrug-resistant A. schubertii DM210910 by using the minimum growth inhibitory concentration and Oxford cup method. In addition, scanning electron microscopy analysis suggested that C-13326 peptide inhibited the growth of A. schubertii DM210910 by damaging the bacterial cell membrane. To explore the role of peptide C-13326 in vivo, hybrid snakehead was fed with peptide C-13326 as feed additives for 7 days. The results revealed that C-13326 peptide could significantly down-regulate the expression levels of IL-1β, IL-8, IL-12 and TNF-α (p < .05), and significantly improved the survival rate of hybrid snakehead after challenging with A. schubertii DM210910. Therefore, the C-13326 peptide is a promising antimicrobial agent for A. schubertii treatment in aquaculture.

Heterologous Production of Antimicrobial Peptides: Notes to Consider

Heavy and irresponsible use of antibiotics in the last century has put selection pressure on the microbes to evolve even faster and develop more resilient strains. In the confrontation with such sometimes called "superbugs", the search for new sources of biochemical antibiotics seems to have reached the limit. In the last two decades, bioactive antimicrobial peptides (AMPs), which are polypeptide chains with less than 100 amino acids, have attracted the attention of many in the control of microbial pathogens, more than the other types of antibiotics. AMPs are groups of components involved in the immune response of many living organisms, and have come to light as new frontiers in fighting with microbes. AMPs are generally produced in minute amounts within organisms; therefore, to address the market, they have to be either produced on a large scale through recombinant DNA technology or to be synthesized via chemical methods. Here, heterologous expression of AMPs within bacterial, fungal, yeast, plants, and insect cells, and points that need to be considered towards their industrialization will be reviewed.

Cecropin AD reduces viral load and inflammatory response against H9N2 avian influenza virus in chickens

Introduction

This study focuses on evaluating the therapeutic efficacy of cecropin AD, an antimicrobial peptide, against H9N2 avian influenza virus (AIV) in chickens. Given the global impact of H9N2 AIV on poultry health, identifying effective treatments is crucial.

Methods

To assess the impact of cecropin AD, we conducted in vivo experiments involving 108 5-week-old chickens divided into control, infected, and various treatment groups based on cecropin AD dosage levels (high, medium, and low). The methodologies included hemagglutination (HA) tests for viral titers, histopathological examination and toluidine blue (TB) staining for lung pathology, real-time PCR for viral detection, and enzyme-linked immunosorbent assays for measuring serum levels of inflammatory markers.

Results

The findings revealed that cecropin AD substantially reduced lung pathology and viral load, especially at higher dosages, comparing favorably with the effects seen from conventional treatments. Moreover, cecropin AD effectively modulated mast cell activity and the levels of inflammatory markers such as IL-6, TNF-α, IFN-γ, and 5-HT, indicating its potential to diminish inflammation and viral spread.

Discussion

Cecropin AD presents a significant potential as an alternative treatment for H9N2 AIV in chickens, as evidenced by its ability to lessen lung damage, decrease viral presence, and adjust immune responses. This positions cecropin AD as a promising candidate for further exploration in the management of H9N2 AIV infections in poultry.

A novel stacking-based predictor for accurate prediction of antimicrobial peptides

Antimicrobial peptides (AMPs) are gaining acceptance and support as a chief antibiotic substitute since they boost human immunity. They retain a wide range of actions and have a low risk of developing resistance, which are critical properties to the pharmaceutical industry for drug discovery. Antibiotic sensitivity, however, is an issue that affects people all around the world and has the potential to one day lead to an epidemic. As cutting-edge therapeutic agents, AMPs are also expected to cure microbial infections. In order to produce tolerable drugs, it is crucial to understand the significance of the basic architecture of AMPs. Traditional laboratory methods are expensive and time-consuming for AMPs testing and detection. Currently, bioinformatics techniques are being successfully applied to the detection of AMPs. In this study, we have developed a novel STacking-based ensemble learning framework for AntiMicrobial Peptide (STAMP) prediction. First, we constructed 84 different baseline models by using 12 different feature encoding schemes and 7 popular machine learning algorithms. Second, these baseline models were trained and employed to create a new probabilistic feature vector. Finally, based on the feature selection strategy, we determined the optimal probabilistic feature vector, which was further utilized for the construction of our stacked model. Resultantly, the STAMP predictor achieved excellent performance during cross-validation with an accuracy and Matthew's correlation coefficient of 0.930 and 0.860, respectively. The corresponding metrics during the independent test were 0.710 and 0.464, respectively. Overall, STAMP achieved a more accurate and stable performance than the baseline models and significantly outperformed the existing predictors, demonstrating the effectiveness of our proposed hybrid framework. Furthermore, STAMP is expected to assist community-wide efforts in identifying AMPs and will contribute to the development of novel therapeutic methods and drug-design for immunity.Communicated by Ramaswamy H. Sarma.

Molecular characterization and antimicrobial activity of cecropin family in Hermetia illucens

Antimicrobial peptides are potential alternatives to traditional antibiotics in the face of increasing bacterial resistance. Insects possess many antimicrobial peptides and have become a valuable source of novel and highly effective antimicrobial peptides. Hermetia illucens as a resource insect, for example, has the highest number of antimicrobial peptides of any dipteran. However, most antimicrobial peptides, especially cecropin, have not been comprehensively identified and have not been evaluated for their antimicrobial ability. In this study, we analyzed the localization and gene structure of 33 cecropin molecules in the H. illucens genome and evaluated their activity against common human pathogens. The results showed that 32 cecropin molecules were concentrated on 1 chromosome, most with 2 exons. More importantly, most of the cecropins had a good antibacterial effect against Gram-negative bacteria, and were not hemolytic. The minimum inhibitory concentration (MIC) of the cecropin designated H3 against E. coli was 4 μg/mL. The toxicity, killing time kinetics, and anti-biofilm activity of H3 were further investigated and confirmed its antimicrobial ability. Overall, H3 is a potential candidate for the development of new antimicrobials to treat severe infections caused by Gram-negative pathogens such as E. coli.

Oxidative stress governs mosquito innate immune signalling to reduce chikungunya virus infection in Aedes-derived cells

Arboviruses such as chikungunya, dengue and zika viruses cause debilitating diseases in humans. The principal vector species that transmits these viruses is the Aedes mosquito. Lack of substantial knowledge of the vector species hinders the advancement of strategies for controlling the spread of arboviruses. To supplement our information on mosquitoes' responses to virus infection, we utilized Aedes aegypti-derived Aag2 cells to study changes at the transcriptional level during infection with chikungunya virus (CHIKV). We observed that genes belonging to the redox pathway were significantly differentially regulated. Upon quantifying reactive oxygen species (ROS) in the cells during viral infection, we further discovered that ROS levels are considerably higher during the early hours of infection; however, as the infection progresses, an increase in antioxidant gene expression suppresses the oxidative stress in cells. Our study also suggests that ROS is a critical regulator of viral replication in cells and inhibits intracellular and extracellular viral replication by promoting the Rel2-mediated Imd immune signalling pathway. In conclusion, our study provides evidence for a regulatory role of oxidative stress in infected Aedes-derived cells.

Insights into midgut cell types and their crucial role in antiviral immunity in the lepidopteran model Bombyx mori

The midgut, a vital component of the digestive system in arthropods, serves as an interface between ingested food and the insect's physiology, playing a pivotal role in nutrient absorption and immune defense mechanisms. Distinct cell types, including columnar, enteroendocrine, goblet and regenerative cells, comprise the midgut in insects and contribute to its robust immune response. Enterocytes/columnar cells, the primary absorptive cells, facilitate the immune response through enzyme secretions, while regenerative cells play a crucial role in maintaining midgut integrity by continuously replenishing damaged cells and maintaining the continuity of the immune defense. The peritrophic membrane is vital to the insect's innate immunity, shielding the midgut from pathogens and abrasive food particles. Midgut juice, a mixture of digestive enzymes and antimicrobial factors, further contributes to the insect's immune defense, helping the insect to combat invading pathogens and regulate the midgut microbial community. The cutting-edge single-cell transcriptomics also unveiled previously unrecognized subpopulations within the insect midgut cells and elucidated the striking similarities between the gastrointestinal tracts of insects and higher mammals. Understanding the intricate interplay between midgut cell types provides valuable insights into insect immunity. This review provides a solid foundation for unraveling the complex roles of the midgut, not only in digestion but also in immunity. Moreover, this review will discuss the novel immune strategies led by the midgut employed by insects to combat invading pathogens, ultimately contributing to the broader understanding of insect physiology and defense mechanisms.

Anti-Herpes Simplex Virus and Anti-Inflammatory Activities of the Melittin Peptides Derived from Apis mellifera and Apis florea Venom

Herpes simplex virus (HSV) is known to cause cold sores and various diseases in humans. Importantly, HSV infection can develop latent and recurrent infections, and it is also known to cause inflammation. These infections are difficult to control, and effective treatment of the disease remains a challenge. Thus, the search for new antiviral and anti-inflammatory agents is a necessity. Melittin is a major peptide that is present in the venom of the honeybee. It possesses a number of pharmacological properties. In this study, the effects of the melittin peptides from A. mellifera (MEL-AM) and A. florea (MEL-AF) against HSV-1 and HSV-2 were evaluated at different stages during the viral multiplication cycle in an attempt to define the mode of antiviral action using plaque reduction and virucidal assays. The results revealed a new finding that melittin at 5 µg/mL demonstrated the highest inhibitory effect on HSV through the direct inactivation of viral particles, and MEL-AF displayed a greater virucidal activity. Moreover, melittin was also observed to interfere with the process of HSV attachment to the host cells. MEL-AM exhibited anti-HSV-1 and anti-HSV-2 effects with EC50 values of 4.90 ± 0.15 and 4.39 ± 0.20 µg/mL, while MEL-AF demonstrated EC50 values of 4.47 ± 0.21 and 3.95 ± 0.61 µg/mL against HSV-1 and HSV-2, respectively. However, non-cytotoxic concentrations of both types of melittin produced only slight degrees of HSV-1 and HSV-2 inhibition after viral attachment, but melittin at 5 µg/mL was able to reduce the plaque size of HSV-2 when compared to the untreated group. In addition, MEL-AM and MEL-AF also exhibited anti-inflammatory activity via the inhibition of nitric oxide production in LPS-stimulated RAW 264.7 macrophage cells, and they were also found to down-regulate the expressions of the iNOS, COX-2 and IL-6 genes. The highest inhibition of IL-6 mRNA expression was found after treatment with 10 µg/mL of MEL-AM and MEL-AF. Therefore, melittin peptides have displayed strong potential to be used as an alternative treatment for HSV infection and inflammatory diseases in the future.

A novel glycine-rich peptide from Zophobas atratus, coleoptericin B, targets bacterial membrane and protects against Klebsiella pneumoniae-induced mastitis in mice

OBJECTIVES

The growing occurrence of bacterial resistance has spawned the development of novel antimicrobial agents. Antimicrobial peptides, a class of small molecules with antimicrobial activity, have been regarded as the ideal alternatives to antibiotics.

METHODS

In this study, we amplified a new type of Zophobas atratus coleoptericin (denoted coleoptericin B) through rapid amplification of cDNA ends (RACE) PCR and expressed recombinant Z. atratus coleoptericin B (rZA-col B) by prokaryotic expression. Subsequently, we evaluated the antimicrobial effect and biocompatibility of rZA-col B in vivo, investigated its antimicrobial mechanism, and assessed its therapeutic effect in a murine model of mastitis caused by MDR Klebsiella pneumoniae.

RESULTS

The in vivo studies demonstrated that rZA-col B possesses broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative bacteria. It exhibited less than 1.5% haemolysis and 10% cytotoxicity, even at a concentration of 128 μM. Additionally, rZA-col B had a minimal risk of inducing drug resistance. Furthermore, rZA-col B could disrupt the integrity of bacterial membranes, induce membrane permeabilization and ultimately lead to bacterial death. Importantly, rZA-col B also alleviated mastitis caused by MDR K. pneumoniae in a murine model by enhancing bacterial clearance, reducing neutrophil infiltration, decreasing TNF-α and IL-1β expression, and protecting the mammary barrier.

CONCLUSIONS

rZA-col B may be a promising antibacterial agent to combat MDR bacterial infection.

Bioactive compounds and biological activity in edible insects: A review

New strategies to combat hunger are a current and urgent demand. The increase in population has generated a high demand for products and services that affect food production, cultivation areas, and climate. Viable and sustainable alternative sources have been sought to meet food quality requirements. In this context, edible insects are a good source of macro-nutrients, and bioactive compounds confer biological properties that improve their nutritional aspects and benefit human health. This review aims to present the benefits and contributions of edible insects from the point of view of the biological contribution of macronutrients, and bioactive compounds, as well as consider some anti-nutritional aspects reported in edible insects. It was found that insects possess most of the macronutrients necessary for human life and are rich in bioactive compounds commonly found in plants. These bioactive compounds can vary significantly depending on the developmental stage, diet, and species of edible insects. However, they also contain phytochemicals in which anti-nutrients predominate, which can adversely affect humans with allergenic reactions or reduced nutrient viability when consumed in high amounts or for prolonged periods. Hydrocyanide, oxalates, soluble oxalate, and phytate are the most studied anti-nutrients. However, the doses at which they occur are far below the limits in foods. In addition, anti-nutrient levels decrease significantly in processing, such as oven-drying and defatting methods. However, there are few studies, so more trials are needed to avoid generalizing. Therefore, edible insects can be considered complete food.

Diversity and antimicrobial activity of the tropical ant-derived actinomycetes isolated from Thailand

Antibiotic resistance is one of the most important global healthcare challenges and is responsible for the mortality of millions of people worldwide every year. It is a crisis attributed to misuse of antibiotics and a lack of new drug development. Actinomycetes constitute a group of Gram-positive bacteria known for their distinctive high guanine-cytosine (G+C) content in their genomic DNA. These microorganisms are widely recognized for their capability to generate a wide range of secondary metabolites with diverse biological activities. These versatile microorganisms are ubiquitous in diverse ecosystems, including soil, freshwater, marine sediments, and within the bodies of insects. A recent study has demonstrated that social insects, such as ants, host a diverse array of these bacteria. In this study, we involved the isolation and characterization of a total of 72 actinomycete strains obtained from 18 distinct ant species collected from various regions across Thailand. Utilizing 16S rRNA gene analysis, these isolated actinomycetes were classified into four distinct genera: Amycolatopsis (2 isolates), Micromonospora (1 isolate), Nocardia (8 isolates), and Streptomyces (61 isolates). Among the Streptomyces strains, 23 isolates exhibited antimicrobial activity against a panel of Gram-positive bacteria, including Bacillus subtilis ATCC 6633, Staphylococcus epidermidis ATCC 12228, Staphylococcus aureus ATCC 25923, Kocuria rhizophila ATCC 9341, and Methicillin-resistant Staphylococcus aureus (MRSA) DMST 20646. Additionally, two isolates displayed antifungal activity against Candida albicans TISTR 5554. Based on 16S rRNA gene sequence similarity studies, these two isolates, ODS25 and ODS28, were demonstrated to be closely related to Streptomyces lusitanus NBRC 13464T (98.07%) and Streptomyces haliclonae DSM 41970T (97.28%), respectively. The level of 16S rRNA gene sequence similarity below 98.65% cutoff indicates its potential as a novel actinomycete species. These findings underscore the potential of actinomycetes sourced from ants as a valuable reservoir of novel antimicrobials.

Machine learning assisted rational design of antimicrobial peptides based on human endogenous proteins and their applications for cosmetic preservative system optimization

Preservatives are essential components in cosmetic products, but their safety issues have attracted widespread attention. There is an urgent need for safe and effective alternatives. Antimicrobial peptides (AMPs) are part of the innate immune system and have potent antimicrobial properties. Using machine learning-assisted rational design, we obtained a novel antibacterial peptide, IK-16-1, with significant antibacterial activity and maintaining safety based on β-defensins. IK-16-1 has broad-spectrum antimicrobial properties against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans, and has no haemolytic activity. The use of IK-16-1 holds promise in the cosmetics industry, since it can serve as a preservative synergist to reduce the amount of other preservatives in cosmetics. This study verified the feasibility of combining computational design with artificial intelligence prediction to design AMPs, achieving rapid screening and reducing development costs.

Entomotherapy as an alternative treatment for diseases due to Gram-negative bacteria in Burkina Faso

Insects are known for their harmful effects. However, they also benefit humans, animals, plants, and ecosystems. Its beneficial uses include entomophagy and entomotherapy. This study aimed to evaluate the antibacterial activity of insect extracts against Gram-negative bacteria. Antibacterial activities of thirteen crude extracts of medicinal insects were tested against twelve Gram-negative bacteria by diffusion on agar. Imipenem was used as an antibiotic for positive control. The thirteen extracts acted differently against certain Gram-negative bacteria. The largest inhibition diameter was for extracts of Cirina butyrospermi and Mylabris variabilis against Pseudomonas aeruginosa ATCC27853 and Salmonella enteritidis ATCC13076, respectively. The diameters of inhibition obtained using imipenem against these same bacterial strains were 13.0 ± 0.0 mm and 22 ± 1.0 mm, respectively. The lowest inhibition diameter (7.5 ± 0.0 mm) was obtained using Anopheles gambiae extract against Salmonella Typhimurium ATCC14028. Imipenem was active on all strains tested. The highest values of the index multi-resistance to insect's extracts were reported for Pseudomonas aeruginosa ATCC9027 and Serratia odorifera 652411. Overall, the results of this study confirmed the antibacterial activities of insects used by traditional health practitioners to treat different pathologies. Entomotherapy could be an alternative treatment for certain infectious pathologies caused by gram-negative bacteria.

Jelleine, a Family of Peptides Isolated from the Royal Jelly of the Honey Bees (Apis mellifera), as a Promising Prototype for New Medicines: A Narrative Review

The jelleine family is a group of four peptides (jelleines I-IV) originally isolated from the royal jelly of honey bee (Apis mellifera), but later detected in some honey samples. These oligopeptides are composed of 8-9 amino acid residues, positively charged (+2 to +3 at pH 7.2), including 38-50% of hydrophobic residues and a carboxamide C-terminus. Jelleines, generated by processing of the C-terminal region of major royal jelly proteins 1 (MRJP-1), play an important biological role in royal jelly conservation as well as in protecting bee larvae from potential pathogens. Therefore, these molecules present numerous benefits for human health, including therapeutic purposes as shown in preclinical studies. In this review, we aimed to evaluate the biological effects of jelleines in addition to characterising their toxicities and stabilities. Jelleines I-III have promising antimicrobial activity and low toxicity (LD50 > 1000 mg/Kg). However, jelleine-IV has not shown relevant biological potential. Jelleine-I, but not the other analogues, also has antiparasitic, healing, and pro-coagulant activities in addition to indirectly modulating tumor cell growth and controlling the inflammatory process. Although it is sensitive to hydrolysis by proteases, the addition of halogens increases the chemical stability of these molecules. Thus, these results suggest that jelleines, especially jelleine-I, are a potential target for the development of new, effective and safe therapeutic molecules for clinical use.

Pathogenicity of microsclerotia from Metarhizium robertsii against Aedes aegypti larvae and antimicrobial peptides expression by mosquitoes during fungal-host interaction

Aedes aegypti is a vector of various disease-causing arboviruses. Chemical insecticide-based methods for mosquito control have increased resistance in different parts of the world. Thus, alternative control agents such as the entomopathogenic fungi are excellent candidates to control mosquitoes as part of an ecofriendly strategy. There is evidence of the potential of entomopathogenic fungal conidia and blastospores for biological control of eggs, larval and adult stages, as well as the pathogenicity of fungal microsclerotia against adults and eggs. However, there are no studies on the pathogenicity of microsclerotia against either aquatic insects or insects that develop part of their life cycle in the water, such as the A. aegypti larvae. In this study, we assayed the production of microsclerotia and their pathogenicity against A. aegypti larvae of two isolates of Metarhizium robertsii, i.e., CEP 423 isolated in La Plata, Argentina, and the model ARSEF 2575. Both isolates significantly reduced the survival of A. aegypti exposed to their microsclerotia. The fungus-larva interaction resulted in a delayed response in the host. This was evidenced by the expression of some humoral immune system genes such as defensins and cecropin on the 9th day post-infection, when the fungal infection was consolidated as a successful process that culminates in larvae mortality. In conclusion, M. robertsii microsclerotia are promising propagules to be applied as biological control agents against mosquitoes since they produce pathogenic conidia against A. aegypti larvae.

Rhynchophorus ferrugineus larvae: A novel source for combating broad-spectrum bacterial and fungal infections

Antimicrobial resistance is a growing concern due to the growth of antibiotic-resistant microorganisms, which makes it difficult to treat infection. Due to its broad-spectrum antimicrobial properties against a diverse array of bacteria, both Gram-positive and Gram-negative bacteria, and fungi, Rhynchophorus ferrugineus larval antimicrobial peptides (AMPs) have demonstrated potential as antimicrobial agents for the treatment of microbial infections and prevention of antibiotic resistance. This study emphasizes the unexplored mechanisms of action of R. ferrugineus larvae against microorganisms. Among the most widely discussed mechanisms is the effect of AMPs in larvae in response to a threat or infection. Modulation of immune-related genes in the intestine and phagocytic capacity of its hemocytes may also affect the antimicrobial activity of R. ferrugineus larvae, with an increase in phenoloxidase activity possibly correlated with microbial clearance and survival rates of larvae. The safety and toxicity of R. ferrugineus larvae extracts, as well as their long-term efficacy, are also addressed in this paper. The implications of future research are explored in this paper, and it is certain that R. ferrugineus larvae have the potential to be developed as a broad-spectrum antimicrobial agent with proper investigation.

Subterranean termites raise the alarm when their anti-fungal weapon falters

Termicin is an anti-fungal defensin that is disseminated from termite salivary glands. The peptide appears to be critical for the elimination with mutual grooming (allogrooming) of pathogenic spores (conidia) that have attached to the insect cuticle. There has been a recent selective sweep for an advantageous variant of this peptide in the subterranean termite Reticulitermes flavipes. We tested the anti-mycotic activity of a recombinant termicin corresponding with this variant against the conidia of different Metarhizium fungal isolates from soil close to foraging R. flavipes workers. Termicin was most effective against isolates that had previously been shown to elicit a relatively weak alarm response, as indicated by brief bouts of rapid longitudinal oscillatory movement (LOM). These isolates that elicited weak alarm were also the deadliest apparently because the survival of termites exposed to the fungus depends on a strong social immune response (LOMs and allogrooming). The selective pressure for a single termicin variant may have been driven by the most dangerous isolates that elicit a weak behavioral response. The correlation between termicin anti-fungal activity and LOM suggests that pathogen-associated molecular patterns that affect termite recognition of conidial contamination and the onset of elevated allogrooming also affect the vulnerability of conidia to the disruption of their cell membranes by termicin.

Effects of chronic exposure to sublethal doses of neonicotinoids in the social wasp Polybia paulista: Survival, mobility, and histopathology

Several studies have investigated the consequences of exposure to neonicotinoids in honeybees. Given the lack of studies concerning the consequences of exposure of social wasps to neonicotinoids, as well as the ecological importance of these insects, the objective of this study was to test the hypothesis that chronic exposure to sublethal concentrations of thiamethoxam decreases survival and mobility by causing damage to the brain and midgut of the social wasp Polybia paulista. The wasps were exposed to different concentrations of thiamethoxam, in order to obtain the mean lethal concentration (LC50), which was used as a reference for calculation of two sublethal concentrations (LC50/100 and LC50/10) employed in subsequent experiments. To calculate survival, groups of exposed (EW) and unexposed (UW) wasps were monitored until death, allowing calculation of the average lethal time. The EW and UW groups were evaluated after 12, 24, 48, and 72 h of exposure, considering their mobility and histopathological parameters of the midgut and brain. A lesion index based on semiquantitative analyses was used for comparison of histopathological damage. The results demonstrated that exposure to the LC50/10 led to a significantly shorter survival time of the P. paulista workers, compared to unexposed wasps. In addition, both sublethal concentrations decreased mobility and caused damage to the intestine (loss of brush border, presence of spherocrystals, loss of cytoplasmic material, and pyknosis) and the brain (loss of cell contact and pyknosis), regardless of the exposure time. The findings showed that, like bees, social wasps are nontarget insects susceptible to the detrimental consequences of neonicotinoid use, with exposure leading to impaired survival, locomotion, and physiology.

Effect of tandem repeats of antimicrobial peptide CC34 on production of target proteins and activity of Pichia pastoris

Antimicrobial peptides (AMPs) are attracting attention in the fields of medicine, food, and agriculture because of their broad-spectrum antibacterial properties, low resistance, and low-residue in the body. However, the low yield and instability of the prepared AMP drugs limit their application. In this study, we designed a tetramer of the AMP CC34, constructed and transfected two recombinant expression vectors with pGAPZαA containing a haploid CC34 and tetraploid CC34 (CC34-4js) into Pichia pastoris to explore the effect of biosynthesized peptides. The results showed that CC34 and CC34-4js expression levels were 648.2 and 1105.3 mg/L, respectively, in the fermentation supernatant of P. pastoris. The CC34-4js tetramer showed no antibacterial activity, could be cleaved to the monomer using formic acid, and the hemolytic rate of the polyploid was slightly lower than that of monomeric CC34. The average daily gain, average daily feed intake, feed conversion ratio and immune organ index of rats fed CC34 and CC34-4js showed no differences. In conclusion, CC34-4js exhibited a higher yield and lower hemolysis in P. pastoris than those of CC34. Finally, CC34 and CC34-4js enterokinase lysates showed similar antibacterial activity and both expressed peptides potentially improved the growth performance and organ indices of rats.

A systematical review on antimicrobial peptides and their food applications

Food safety issues are a major concern in food processing and packaging industries. Food spoilage is caused by microbial contamination, where antimicrobial peptides (APs) provide solutions by eliminating microorganisms. APs such as nisin have been successfully and commonly used in food processing and preservation. Here, we discuss all aspects of the functionalization of APs in food applications. We briefly review the natural sources of APs and their native functions. Recombinant expression of APs in microorganisms and their yields are described. The molecular mechanisms of AP antibacterial action are explained, and this knowledge can further benefit the design of functional APs. We highlight current utilities and challenges for the application of APs in the food industry, and address rational methods for AP design that may overcome current limitations.

Octominin: An antimicrobial peptide with antibacterial and anti-inflammatory activity against carbapenem-resistant Escherichia coli both in vitro and in vivo

OBJECTIVES

The emergence of carbapenem-resistant Escherichia coli (CREC) is a global concern as its prevalence restricts treatment options and poses a considerable threat to public health. In this study, in vitro and in vivo activity of the antimicrobial peptide Octominin against CREC was investigated to reveal possible mechanisms of action. Furthermore, its safety and factors influencing its antibacterial effect were assessed. Additionally, the anti-inflammatory effects of Octominin were examined.

METHODS

The antimicrobial activity of Octominin against 11 strains of CREC was determined using the broth microdilution method, growth curve, and time-kill assay. Its possible mechanism of action was unraveled using the propidium iodide and N-phenyl-1-naphthylamine fluorochrome and lipopolysaccharide-binding assays. To understand the safety and stability of Octominin, its cytotoxicity, hemolysis, and antibacterial activity under various conditions (i.e, temperature, ions) were estimated. Additionally, a Galleria mellonella infection model was utilized to evaluate the efficacy of Octominin in vivo, and qRT-PCR was performed to assess its effect on the expression of proinflammatory cytokines.

RESULTS

Octominin displayed a significant antibacterial effect, with MICs of 4-8 µg/mL and MBCs of 8-16 µg/mL. Octominin exerted its antibacterial effect by disrupting bacterial membranes. Cytotoxicity and hemolysis tests demonstrated the potential application of Octominin in vivo. The G. mellonella infection model asserted the in vivo efficacy of Octominin. Furthermore, Octominin inhibited the expression of proinflammatory cytokines. Although the temperature had little effect on its the activity, serum and ions reduced activity.

CONCLUSION

Octominin is a promising alternative agent with remarkable antibacterial and anti-inflammatory effects for treating infections caused by CREC.

Effect of Camel Peptide on the Biofilm of Staphylococcus epidermidis and Staphylococcus haemolyticus Formed on Orthopedic Implants

The increasing bacterial drug resistance and the associated challenges in the treatment of infections warrant the search for alternative therapeutic methods. Hope is placed in antimicrobial peptides, which have a broad spectrum of action and are effective against strains which are resistant to conventional antibiotics. Antimicrobial peptides are also tested for their efficacy in the treatment of infections associated with the formation of biofilm. The aim of the present study was to examine the effect of Camel peptide on S. epidermidis and S. haemolyticus adhesion to and formation of biofilm on steel cortical bone screws and also on the process of reducing mature biofilm in orthopedic implants. The tests were performed on steel implants for osteosynthesis. The MIC value and MBEC values of the peptide were determined using the microdilution method in microtiter plates. The effect of the peptide on adhesion and biofilm formation, as well as on the activity on the preformed biofilm, was evaluated using quantitative methods and confocal microscopy. The presented research results indicate that the peptide exhibits very good antimicrobial properties against the analyzed strains. Concentrations above MIC reduced biofilm in the range of 90-99%.

Identification and immune analysis of antimicrobial peptides from the cigarette beetle (Lasioderma serricorne)

Antimicrobial peptides (AMPs) in insects are endogenous peptides that are effector components of the innate defense system of the insect. AMPs may serve as antimicrobial agents because of their small molecular weight and broad-spectrum antimicrobial activity. In this study, we performed transcriptome analysis of cigarette beetle (Lasioderma serricorne) larvae, parasitized by the ectoparasitic wasp, Anisopteromalus calandrae. Several AMP genes were significantly upregulated following A. calandrae parasitism, postulating the hypothesis that the parasitization enhanced the host's resistance against pathogenic microorganisms through the regulation of host AMP genes. Specifically, 3 AMP genes (LsDef1, LsDef2, and LsCole) were significantly upregulated and we studied their immune function in L. serricorne. Immune challenge and functional analysis showed that LsCole was responsible for the immune response against Gram-negative and Gram-positive bacteria, while LsDef1 and LsDef2 were involved in insect defense against Gram-positive bacteria. Purified recombinant LsCole exhibited antimicrobial activities against the Gram-negative bacterium Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. LsDef2 showed an antibacterial effect against S. aureus. LsCole and LsDef2 exhibited antibiofilm activity against S. aureus. The 2 AMPs disrupted cell membranes and caused leakage of S. aureus cell contents. The results indicated that the 3 AMPs in L. serricorne are involved in the innate immunity of this pest insect. These AMPs may have potential as antimicrobial agents for bacterial infection chemotherapy. Hence, data are discussed in relation to new control strategies with greater biosafety against pest insects with use of microbial biocontrol agents in combination with RNA interference against the insect's defensive AMP genes.

Efficient Delivery of Antimicrobial Peptides in an Innovative, Slow-Release Pharmacological Formulation

Both nanostructure and multivalency enhance the biological activities of antimicrobial peptides (AMPs), whose mechanism of action is cooperative. In addition, the efficacy of a particular AMP should benefit from a steady concentration at the local place of action and, therefore, from a slow release after a dynamic repository. In the context of emerging multi-resistant bacterial infections and the urgent need for novel and effective antimicrobial drugs, we tested these concepts through the engineering of four AMPs into supramolecular complexes as pharmacological entities. For that purpose, GWH1, T22, Pt5, and PaD, produced as GFP or human nidogen-based His-tagged fusion proteins, were engineered as self-assembling oligomeric nanoparticles ranging from 10 to 70 nm and further packaged into nanoparticle-leaking submicron granules. Since these materials slowly release functional nanoparticles during their time-sustained unpacking, they are suitable for use as drug depots in vivo. In this context, a particular AMP version (GWH1-NIDO-H6) was selected for in vivo validation in a zebrafish model of a complex bacterial infection. The GWH1-NIDO-H6-secreting protein granules are protective in zebrafish against infection by the multi-resistant bacterium Stenotrophomonas maltophilia, proving the potential of innovative formulations based on nanostructured and slowly released recombinant AMPs in the fight against bacterial infections.

Transcriptome analysis of Corvus splendens reveals a repertoire of antimicrobial peptides

Multidrug resistance has become a global health problem associated with high morbidity and mortality. Antimicrobial peptides have been acknowledged as potential leads for prospective anti-infectives. Owing to their scavenging lifestyle, Corvus splendens is thought to have developed robust immunity to pathogens found in their diet, implying that they have evolved mechanisms to resist infection. In the current study, the transcriptome of C. splendens was sequenced, and de novo assembled to identify the presence of antimicrobial peptide genes. 72.09 million high-quality clean reads were obtained which were then de novo assembled into 3,43,503 transcripts and 74,958 unigenes. About 37,559 unigenes were successfully annotated using SwissProt, Pfam, GO, and KEGG databases. A search against APD3, CAMPR3 and LAMP databases identified 63 AMP candidates belonging to more than 20 diverse families and functional classes. mRNA of AvBD-2, AvBD-13 and CATH-2 were found to be differentially expressed between the three tested crows as well as among the tissues. We also characterized Corvus Cathelicidin 2 (CATH-2) to gain knowledge of its antimicrobial mechanisms. The CD spectroscopy of synthesized mature Corvus CATH-2 peptide displayed an amphipathic α-helical structure. Though the synthetic CATH-2 caused hemolysis of human RBC, it also exhibited antimicrobial activity against E. coli, S. aureus, and B. cereus. Docking simulation results revealed that this peptide could bind to the LPS binding site of MD-2, which may prevent LPS from entering the MD-2 binding pocket, and trigger TLR4 signaling pathway. The Corvus CATH-2 characterized in this study could aid in the development of novel therapeutics.

The Development of New Methods to Stimulate the Production of Antimicrobial Peptides in the Larvae of the Black Soldier Fly Hermetia illucens

(1) The global population is projected to reach a staggering 9.8 billion people by the year 2050, leading to major concerns about food security. The necessity to increase livestock production is inevitable. The black soldier fly (BSF) is known for its ability to consume a wide range of organic waste, and BSF larvae have already been used as a partial substitute for fishmeal. In contrast, the use of antibiotics in livestock feed for growth promotion and prophylaxis poses a severe threat to global health owing to antimicrobial resistance. Insect antimicrobial peptides (AMPs) have shown the potential to rapidly disrupt target bacterial membranes, making bacterial resistance to AMPs a less likely concern. (2) In this study, we explored various methods for stimulating AMP synthesis in BSF larvae and found that thermal injury effectively induced the production of various AMP types. Additionally, we investigated the activation of innate immune response pathways that lead to AMP production following thermal injury. (3) Interestingly, thermal injury treatment, although not involving bacteria, exhibited a similar response to that observed following Gram-positive bacterial infection in eliciting the expression of AMP genes. (4) Our findings offer support for the industrial use of BSF to enhance livestock production and promote environmental health.

Insect Microbial Symbionts: Ecology, Interactions, and Biological Significance

The guts of insect pests are typical habitats for microbial colonization and the presence of bacterial species inside the gut confers several potential advantages to the insects. These gut bacteria are located symbiotically inside the digestive tracts of insects and help in food digestion, phytotoxin breakdown, and pesticide detoxification. Different shapes and chemical assets of insect gastrointestinal tracts have a significant impact on the structure and makeup of the microbial population. The number of microbial communities inside the gastrointestinal system differs owing to the varying shape and chemical composition of digestive tracts. Due to their short generation times and rapid evolutionary rates, insect gut bacteria can develop numerous metabolic pathways and can adapt to diverse ecological niches. In addition, despite hindering insecticide management programs, they still have several biotechnological uses, including industrial, clinical, and environmental uses. This review discusses the prevalent bacterial species associated with insect guts, their mode of symbiotic interaction, their role in insecticide resistance, and various other biological significance, along with knowledge gaps and future perspectives. The practical consequences of the gut microbiome and its interaction with the insect host may lead to encountering the mechanisms behind the evolution of pesticide resistance in insects.

In-depth biological characterization of two black soldier fly anti-Pseudomonas peptides reveals LPS-binding and immunomodulating effects

As effector molecules of the innate immune system, antimicrobial peptides (AMPs) have gathered substantial interest as a potential future generation of antibiotics. Here, we demonstrate the anti-Pseudomonas activity and lipopolysaccharide (LPS)-binding ability of HC1 and HC10, two cecropin peptides from the black soldier fly (Hermetia Illucens). Both peptides are active against a wide range of Pseudomonas aeruginosa strains, including drug-resistant clinical isolates. Moreover, HC1 and HC10 can bind to lipid A, the toxic center of LPS and reduce the LPS-induced nitric oxide and cytokine production in murine macrophage cells. This suggests that the peptide-LPS binding can also lower the strong inflammatory response associated with P. aeruginosa infections. As the activity of AMPs is often influenced by the presence of salts, we studied the LPS-binding activity of HC1 and HC10 in physiological salt concentrations, revealing a strong decrease in activity. Our research confirmed the early potential of HC1 and HC10 as starting points for anti-Pseudomonas drugs, as well as the need for structural or formulation optimization before further preclinical development can be considered. IMPORTANCE The high mortality and morbidity associated with Pseudomonas aeruginosa infections remain an ongoing challenge in clinical practice that requires urgent action. P. aeruginosa mostly infects immunocompromised individuals, and its prevalence is especially high in urgent care hospital settings. Lipopolysaccharides (LPSs) are outer membrane structures that are responsible for inducing the innate immune cascade upon infection. P. aeruginosa LPS can cause local excessive inflammation, or spread systemically throughout the body, leading to multi-organ failure and septic shock. As antimicrobial resistance rates in P. aeruginosa infections are rising, the research and development of new antimicrobial agents remain indispensable. Especially, antimicrobials that can both kill the bacteria themselves and neutralize their toxins are of great interest in P. aeruginosa research to develop as the next generation of drugs.

Strategies to combat Gram-negative bacterial resistance to conventional antibacterial drugs: a review

The emergence of antimicrobial resistance raises the fear of untreatable diseases. Antimicrobial resistance is a multifaceted and dynamic phenomenon that is the cumulative result of different factors. While Gram-positive pathogens, such as methicillin-resistant Staphylococcus aureus and Clostridium difficile, were previously the most concerning issues in the field of public health, Gram-negative pathogens are now of prime importance. The World Health Organization's priority list of pathogens mostly includes multidrug-resistant Gram-negative organisms particularly carbapenem-resistant Enterobacterales, carbapenem-resistant Pseudomonas aeruginosa, and extensively drug-resistant Acinetobacter baumannii. The spread of Gram-negative bacterial resistance is a global issue, involving a variety of mechanisms. Several strategies have been proposed to control resistant Gram-negative bacteria, such as the development of antimicrobial auxiliary agents and research into chemical compounds with new modes of action. Another emerging trend is the development of naturally derived antibacterial compounds that aim for targets novel areas, including engineered bacteriophages, probiotics, metal-based antibacterial agents, odilorhabdins, quorum sensing inhibitors, and microbiome-modifying agents. This review focuses on the current status of alternative treatment regimens against multidrug-resistant Gram-negative bacteria, aiming to provide a snapshot of the situation and some information on the broader context.

An Update on the Therapeutic Potential of Antimicrobial Peptides against Acinetobacter baumannii Infections

The rise in antibiotic-resistant strains of clinically important pathogens is a major threat to global health. The World Health Organization (WHO) has recognized the urgent need to develop alternative treatments to address the growing list of priority pathogens. Antimicrobial peptides (AMPs) rank among the suggested options with proven activity and high potential to be developed into effective drugs. Many AMPs are naturally produced by living organisms protecting the host against pathogens as a part of their innate immunity. Mechanisms associated with AMP actions include cell membrane disruption, cell wall weakening, protein synthesis inhibition, and interference in nucleic acid dynamics, inducing apoptosis and necrosis. Acinetobacter baumannii is a critical pathogen, as severe clinical implications have developed from isolates resistant to current antibiotic treatments and conventional control procedures, such as UV light, disinfectants, and drying. Here, we review the natural AMPs representing primary candidates for new anti-A. baumannii drugs in post-antibiotic-era and present computational tools to develop the next generation of AMPs with greater microbicidal activity and reduced toxicity.

Functional Peptides for Plant Disease Control

Plant disease control requires novel approaches to mitigate the spread of and losses caused by current, emerging, and re-emerging diseases and to adapt plant protection to global climate change and the restrictions on the use of conventional pesticides. Currently, disease management relies mainly on biopesticides, which are required for the sustainable use of plant-protection products. Functional peptides are candidate biopesticides because they originate from living organisms or are synthetic analogs and provide novel mechanisms of action against plant pathogens. Hundreds of compounds exist that cover an extensive range of activities against viruses, bacteria and phytoplasmas, fungi and oomycetes, and nematodes. Natural sources, chemical synthesis, and biotechnological platforms may provide peptides at large scale for the industry and growers. The main challenges for their use in plant disease protection are (a) the requirement of stability in the plant environment and counteracting resistance in pathogen populations, (b) the need to develop suitable formulations to increase their shelf life and methods of application, (c) the selection of compounds with acceptable toxicological profiles, and (d) the high cost of production for agricultural purposes. In the near future, it is expected that several functional peptides will be commercially available for plant disease control, but more effort is needed to validate their efficacy at the field level and fulfill the requirements of the regulatory framework.

Partner of neuropeptide bursicon homodimer pburs mediates a novel antimicrobial peptide Ten3LP via Dif/Dorsal2 in Tribolium castaneum

Bursicon is a cystine knot family neuropeptide, composed of two subunits, bursicon (burs) and partner of burs (pburs). The subunits can form heterodimers to regulate cuticle tanning and wing maturation and homodimers to signal different biological functions in innate immunity, midgut stem cell proliferation and energy homeostasis, and reproductive physiology in the model insects Drosophila melanogaster or Tribolium castaneum. Here, we report on the role of the pburs homodimer in signaling innate immunity in T. castaneum larvae. Through transcriptome analysis we identified a set of immune-related genes that respond to pburs RNAi. Treating larvae with recombinant-pburs protein led to up-regulation of antimicrobial peptide (AMP) genes in vivo and in vitro. The upregulation of most AMP genes was dependent on the NF-κB transcription factor Relish. Most importantly, we identified a novel AMP, Tenecin 3-like peptide (Ten3LP), regulated by pburs via NF-κB transcription factor Dorsal-related immunity factor (Dif)/Dorsal2, but not Relish. We conducted Ten3LP RNAi, synthesized recombinant Ten3LP protein for microbial inhibition assays and functionally characterized Ten3LP as an AMP specific for fungi and Gram-positive bacteria. We demonstrate that expression of Ten3LP is activated by pburs via the Toll pathway. These findings identify new molecular targets for development of potential antibiotics for treating microbial infections and perhaps for RNAi based pest management technology.

A systematic review of experimental studies on Salmonella persistence in insects

The consumption of insects as food and feed has been recently suggested as a possible alternative to the rising global food need, thus it is crucial to monitor any potential food safety hazards in the insect supply chain. The aims of this systematic review were to collect, select, and evaluate studies investigating the persistence of Salmonella in insects. We searched PUBMED, EMBASE, WEB of Science Core Collection, and Food Science and Technology Abstracts. In total, 36 papers investigating the persistence of Salmonella in insects (both holometabolous and heterometabolous) were included after screening. Regarding complete metamorphosis insects, the longest Salmonella persistence was reported in Phormia regina, in which the pathogen persisted for 29 days at 5 °C. Similarly, Salmonella persisted in the feces of Alphitobius diaperinus for 28 days. The incomplete metamorphosis insect showing the longest Salmonella persistence (>10 months) was Blatella germanica. Periplaneta americana excreted Salmonella via feces for 44 days until all the insects were dead. The retrieved data on the persistence of Salmonella can be useful for further analysis by risk assessors and decision-makers involved in the safety of insect-based food, contributing to defining the sanitary requirements and risk mitigation measures along the supply chain. The review protocol is registered in PROSPERO database (CRD42022329213).

Mode of action of antimicrobial agents albofungins in eradicating penicillin- and cephalosporin-resistant Vibrio parahaemolyticus biofilm

Albofungin is a promising broad-spectrum antimicrobial compound against multidrug-resistant bacteria. In the present study, we further investigated albofungin's biofilm eradication activity and its potential mode of action against drug-resistant Vibrio parahaemolyticus. Among all derivatives, albofungin exhibited the best antibiofilm and antibacterial activity with rapid killing effects at 0.12 µg mL-1. Confocal microscopy observation exhibited that albofungin disrupted V. parahaemolyticus biofilms by killing or dispersing biofilm cells. Meanwhile, scanning electron microscope and fluorescent staining experiments demonstrated that albofungin rapidly destroyed the integrity and permeability of the bacterial cell membrane. Moreover, this study revealed an antibiofilm mechanism of albofungin involving inhibition of peptidoglycan biosynthesis, flagella assembly pathways, and secretion system proteins in V. parahaemolyticus by quantitative proteomics and validation experiments. Our results highlighted albofungin's mechanism of action in planktonic cells and biofilms and suggested further development and potential applications of albofungin for treating infections caused by penicillins-and-cephalosporins-resistant V. parahaemolyticus. IMPORTANCE Infections caused by multidrug-resistant bacteria, as well as a scarcity of new antibiotics, have become a major health threat worldwide. To tackle the demand for new and effective treatments, we investigated the mechanism of action of albofungin, a natural product derived from Streptomyces, which exhibits potent antimicrobial activity against multidrug-resistant bacteria. Albofungin showed potent biofilm eradication activity against penicillins-and-cephalosporins-resistant Vibrio parahaemolyticus, which expresses a novel metallo-β-lactamase and, thus, reduces their sensitivity to various antibiotics. We observed membrane disruption and permeation mechanisms in planktonic cells and biofilms after albofungin treatment, while albofungin had a weak interaction with bacterial DNA. Moreover, the antibiofilm mechanism of albofungin included inhibition of peptidoglycan biosynthesis, flagellar assembly pathways, and secretion system proteins. Our finding suggested potential applications of albofungin as an antibacterial and antibiofilm therapeutic agent.

Mechanisms and regulation of defensins in host defense

As a family of cationic host defense peptides, defensins are mainly synthesized by Paneth cells, neutrophils, and epithelial cells, contributing to host defense. Their biological functions in innate immunity, as well as their structure and activity relationships, along with their mechanisms of action and therapeutic potential, have been of great interest in recent years. To highlight the key research into the role of defensins in human and animal health, we first describe their research history, structural features, evolution, and antimicrobial mechanisms. Next, we cover the role of defensins in immune homeostasis, chemotaxis, mucosal barrier function, gut microbiota regulation, intestinal development and regulation of cell death. Further, we discuss their clinical relevance and therapeutic potential in various diseases, including infectious disease, inflammatory bowel disease, diabetes and obesity, chronic inflammatory lung disease, periodontitis and cancer. Finally, we summarize the current knowledge regarding the nutrient-dependent regulation of defensins, including fatty acids, amino acids, microelements, plant extracts, and probiotics, while considering the clinical application of such regulation. Together, the review summarizes the various biological functions, mechanism of actions and potential clinical significance of defensins, along with the challenges in developing defensins-based therapy, thus providing crucial insights into their biology and potential clinical utility.

Effect of the rearing diet on gene expression of antimicrobial peptides in Hermetia illucens (Diptera: Stratiomyidae)

Insect proteins have been proposed for human and animal food production. Safeguarding the health status of insects in mass rearing allows to obtain high-quality products and to avoid severe economic losses due to entomopathogens. Therefore, new strategies for preserving insect health must be implemented. Modulation of the insect immune system through the diet is one such strategy. We evaluated gene expression of two antimicrobial peptides (one defensin and one cecropin) in Hermetia illucens (L.) (Diptera: Stratiomyidae) reared on different diets. Analyses were performed on prepupae and 10-day-old larvae reared on cereal- and municipal organic waste-based diets and on only prepupae reared on a cereal-based diet supplemented with sunflower, corn, or soybean oil. The inclusion of sunflower oil at different points in the cereal-based diet was also evaluated. Moreover, diet-driven differences in the inhibitory activity of the hemolymph were tested against Escherichia coli DH5α and Micrococcus yunnanensis HI55 using diffusion assays in solid media. Results showed that a municipal organic waste-based diet produced a significant overexpression of antimicrobial peptides only in prepupae. Inclusion of vegetable oils caused an upregulation of at least one peptide, except for the corn oil. Higher expression of both genes was observed when sunflower oil was added 5 days before pupation. All hemolymph samples showed an inhibitory activity against bacteria colonies. Our results suggest that municipal organic waste-based diet and vegetable oil-added diet may successfully impact the immune system of H. illucens. Such alternatives may also exist for other species of economic interest.

Antimicrobial Peptides in Infectious Diseases and Beyond-A Narrative Review

Despite recent medical research and clinical practice developments, the development of antimicrobial resistance (AMR) significantly limits therapeutics for infectious diseases. Thus, novel treatments for infectious diseases, especially in this era of increasing AMR, are urgently needed. There is ongoing research on non-classical therapies for infectious diseases utilizing alternative antimicrobial mechanisms to fight pathogens, such as bacteriophages or antimicrobial peptides (AMPs). AMPs are evolutionarily conserved molecules naturally produced by several organisms, such as plants, insects, marine organisms, and mammals, aiming to protect the host by fighting pathogenic microorganisms. There is ongoing research regarding developing AMPs for clinical use in infectious diseases. Moreover, AMPs have several other non-medical applications in the food industry, such as preservatives, animal husbandry, plant protection, and aquaculture. This review focuses on AMPs, their origins, biology, structure, mechanisms of action, non-medical applications, and clinical applications in infectious diseases.

Transfer of Cd along the food chain: The susceptibility of Hyphantria cunea larvae to Beauveria bassiana under Cd stress

Heavy metal can affect the bio-control efficiency of entomopathogenic fungi on pests, but this has not been studied in the food chain. Here, the food chain of soil-Fraxinus mandshurica-Hyphantria cunea was constructed to investigate the effect of cadmium (Cd) exposure on the susceptibility of H. cunea larvae to Beauveria bassiana (Bb) and to analyze the corresponding mechanism through larval innate immunity and energy metabolism. Cd through the food chain synergistically enhanced the susceptibility of H. cunea larvae to Bb. Cellular immunity-related parameters decreased when the Cd treatment group was compared with the control group and when the combined treatment group of Cd and Bb was compared with the Bb treatment group. Cd exposure induced hormesis on pathogen recognition and signal transduction genes of humoral immunity, but reduced the expression of effector genes. The expression of the 13 humoral immunity-related genes in the combined treatment group was lower than in the Bb treatment group. Cd exposure decreased the energy storage of H. cunea larvae before Bb infection and aggravated the disorder level of energy metabolism after Bb infection. Taken together, disturbance of innate immunity and energy metabolism improves the susceptibility of H. cunea larvae to Bb in the Cd-polluted food chain.

Insect Meals and Insect Antimicrobial Peptides as an Alternative for Antibiotics and Growth Promoters in Livestock Production

The extensive use of antibiotics in animal production has led to the development of antibiotic-resistant microorganisms and the search for alternative antimicrobial agents in animal production. One such compound may be antimicrobial peptides (AMPs), which are characterized by, among others, a wide range of biocidal activity. According to scientific data, insects produce the largest number of antimicrobial peptides, and the changing EU legislation has allowed processed animal protein derived from insects to be used in feed for farm animals, which, in addition to a protein supplement, may prove to be an alternative to antibiotics and antibiotic growth promoters due to their documented beneficial impact on livestock health. In animals that were fed feeds with the addition of insect meals, changes in their intestinal microbiota, strengthened immunity, and increased antibacterial activity were confirmed to be positive effects obtained thanks to the insect diet. This paper reviews the literature on sources of antibacterial peptides and the mechanism of action of these compounds, with particular emphasis on insect antibacterial peptides and their potential impact on animal health, and legal regulations related to the use of insect meals in animal nutrition.

Microbial Species-Area Relationships on the Skins of Amphibian Hosts

Unlike species-area relationships (SARs) that have been widely reported for plants and animals on Earth, there is no clear understanding of the SARs for microorganisms. In this study, 358 specimens of 10 amphibian host species collected from the rural Chengdu region of southwest China were selected as island models for evaluating SAR curve shapes and assessing the skin microbiota from different amphibian species. The results showed that skin microbial diversity, measured using Hill's number, presented significant differences between hosts, but the difference was insignificant between habitat-specific classifications of hosts. As for microbial SARs, other than the classical power-law (PL) model describing an expected steady increase in microbial diversity as sampled skin area increases, two additional trends were observed: (i) microbial diversity first rises and gradually decreases after reaching a maximum accrual diversity (MaxAD) and (ii) microbial diversity decreases and starts to rise after reaching the minimum accrual diversity (MinAD). Among the four SAR statistical models compared, it was consistently found that the models that can describe MaxAD were favorably selected in the highest frequency. Models that can describe MinAD and PL model also performed reasonably well. However, PL had the poorest fitting power, implying the necessity of introducing biologically meaningful complex SAR models in microbial diversity research. In conclusion, through multihost analyses, our study provided compelling evidence that microbial SARs are complex and nonlinear. A variety of ecological mechanisms may be used for explaining these, including, but not limited to, community saturation, small-island effects, or sampling heterogeneity. IMPORTANCE In this study, we investigate species-area relationships (SARs) for skin-borne symbiotic microbes of wildlife hosts. Unlike the traditional SARs for plants and animals, symbiotic microbial SARs were complex. We found that both U-shaped and inverted U-shaped SAR models were widely favored for microbial taxa than the well-known power-law model in different host species. These favored models presented interesting statistical features, including minimal or maximal accrual diversity or inflection point. We provide intuitive derivations of these statistical properties. We showed that different habitat-specific amphibian hosts did not present distinct microbial diversity and skin-related SAR patterns. We predicted that approximately 600 to 1,400 cm2 (in two-dimensional [2D] measurement) or approximately 1,200 to 3 500 cm2 (in 3D measurement) are the skin area threshold range that can allow the emergence of minimal or maximal accrual microbial diversity with high chances. Finally, we list a variety of ecological mechanisms that may be used for explaining the observed nonlinear SAR trends.

Lipids as a key element of insect defense systems

The relationship between insect pathogenic fungi and their insect hosts is a classic example of a co-evolutionary arms race between pathogen and target host: parasites evolve towards mechanisms that increase their advantage over the host, and the host increasingly strengthens its defenses. The present review summarizes the literature data describing the direct and indirect role of lipids as an important defense mechanism during fungal infection. Insect defense mechanisms comprise anatomical and physiological barriers, and cellular and humoral response mechanisms. The entomopathogenic fungi have the unique ability to digest the insect cuticle by producing hydrolytic enzymes with chitin-, lipo- and proteolytic activity; besides the oral tract, cuticle pays the way for fungal entry within the host. The key factor in insect resistance to fungal infection is the presence of certain types of lipids (free fatty acids, waxes or hydrocarbons) which can promote or inhibit fungal attachment to cuticle, and might also have antifungal activity. Lipids are considered as an important source of energy, and as triglycerides are stored in the fat body, a structure analogous to the liver and adipose tissue in vertebrates. In addition, the fat body plays a key role in innate humoral immunity by producing a range of bactericidal proteins and polypeptides, one of which is lysozyme. Energy derived from lipid metabolism is used by hemocytes to migrate to the site of fungal infection, and for phagocytosis, nodulation and encapsulation. One polyunsaturated fatty acid, arachidonic acid, is used in the synthesis of eicosanoids, which play several crucial roles in insect physiology and immunology. Apolipoprotein III is important compound with antifungal activity, which can modulate insect cellular response and is considered as important signal molecule.

Characterization and transcriptomic analysis of a native fungal pathogen against the rice pest Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive pests of rice. Given the threats posed by insecticide resistance to its control, eco-friendly strategies based on microbial pathogens emerged as a promising biocontrol alternative. In the present study, we isolated a native fungal pathogen against BPH from infected BPH cadavers and preliminarily identified as a strain of Aspergillus fumigatus based on morphological and molecular methods. Laboratory bioassay revealed that this fungal strain was highly virulent to BPH both at nymphal and adult stages, with the median lethal times (LT₅₀) of 7.5 and 5.8 days under high conidial concentration of 1 × 10⁹ conidia mL^-1. A genome-wide view of gene expressions in BPH against fungal attack was analyzed by transcriptomic sequencing and consequently a large number of differentially expressed genes that mainly involved in host immune defense and cell detoxification were found. RNAi-mediated knockdown of an upregulated gene encoding a serine protease (NlSPN) could cause a significant decrease in BPH survival. Combination of dsRNA injection and fungal infection showed an additive effect on BPH mortality, which provided clues to develop new pest management strategies against BPH.

Specific Expression of Antimicrobial Peptides from the Black Soldier Fly in the Midgut of Silkworms (Bombyx mori) Regulates Silkworm Immunity

Antimicrobial peptides are molecules with strong antimicrobial activity and are of substantial interest for the immunization of insects. As a type of dipteran insect that can turn organic waste into animal feed, the black soldier fly (BSF) can "turn waste into treasure". In this study, we investigated the antimicrobial activity of the antimicrobial peptide genes, HiCG13551 and Hidiptericin-1, of BSF in silkworms, by overexpressing the genes specifically in the midgut. Changes in the mRNA levels of the transgenic silkworms after infection with Staphylococcus aureus were evaluated using transcriptome sequencing. The results showed that Hidiptericin-1 had stronger antimicrobial activity than HiCG13551. KEGG enrichment analysis showed that the differentially expressed genes in the transgenic overexpressed Hidiptericin-1 silkworm lines from the D9L strain were mainly enriched in the starch and sucrose metabolism, pantothenate and CoA biosynthesis, drug metabolism (other enzymes), biotin metabolism, platinum drug resistance, galactose metabolism, and pancreatic secretion pathways. In addition, immune-related genes were up-regulated in this transgenic silkworm strain. Our study may provide new insights for future immune studies on insects.