Antimicrobial peptides: their role as infection-selective tracers for molecular imaging

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

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

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

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

Peptide derived from plant defensins: A promising 68Ga radiolabelled agent for diagnostic of infection foci in PET

The development of new radiopharmaceuticals for the detection of hidden infection foci has great relevance for early detection and the selection of the correct treatment, particularly in immunosuppressed patients. In that sense, the labelling of antimicrobial peptides (AMPs) that are capable of binding specifically to the pathogenic microorganism which causes the infection, should provide a sufficiently specific agent, able to distinguish an infection from a sterile inflammation. Defensins are particularly interesting molecules with antimicrobial activity, the EcgDf1 defensin was identified from the genome of a Uruguayan native plant, Erythrina crista-galli, the 'Ceibo' tree. Our group has previously reported a synthetic biologically active short analogue EcgDf21 (ERFTGGHCRGFRRRCFCTKHC) successfully labelled with 99mTc. Herein we present a shorter analogue which also preserves the γ-core domain, as a pharmacophore for a potential infection detection agent. This peptide was derivatized with the bifunctional chelating agent 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) through a lysine linker in the amino-terminal group (NOTA-KGHCRGFRRRC) and radiolabelled with 68Ga ([68Ga]Ga-NOTA-K-EcgDf1(10)). The [68Ga]Ga-NOTA-K-EcgDf1(10) labelling procedure rendered a product with high radiochemical purity and stability in the labelling milieu. The Log P value indicated that the complex has a hydrophilic behaviour, confirmed by the biodistribution profile. The [68Ga]Ga-NOTA-K-EcgDf1(10) complex demonstrated specific binding to cultures of Candida albicans and Aspergillus niger. Its biodistribution showed renal elimination and low accumulation in the rest of the body. It was possible to successfully differentiate sterile inflammation from infection by PET images in nude mice with a target/non-target ratio of 3.3 for C. albicans and 3.7 for A. niger, respectively.

How can biomaterial-conjugated antimicrobial peptides fight bacteria and be protected from degradation?

The emergence of antibiotic-resistant bacteria is a serious threat to public health. Antimicrobial peptides (AMP) are a powerful alternative to antibiotics due to their low propensity to induce bacterial resistance. However, cytotoxicity and short half-lives have limited their clinical translation. To overcome these problems, AMP conjugation has gained relevance in the biomaterials field. Nevertheless, few studies describe the influence of conjugation on enzymatic protection, mechanism of action and antimicrobial efficacy. This review addresses this gap by providing a detailed comparison between conjugated and soluble AMP. Additionally, commonly employed chemical reactions and factors to consider when promoting AMP conjugation are reviewed. The overall results suggested that AMP conjugated onto biomaterials are specifically protected from degradation by trypsin and/or pepsin. However, sometimes, their antimicrobial efficacy was reduced. Due to limited conformational freedom in conjugated AMP, compared to their soluble forms, they appear to act initially by creating small protuberances on bacterial membranes that may lead to the alteration of membrane potential and/or formation of holes, triggering cell death. Overall, AMP conjugation onto biomaterials is a promising strategy to fight infection, particularly associated to the use of medical devices. Nonetheless, some details need to be addressed before conjugated AMP reach clinical practice. STATEMENT OF SIGNIFICANCE: Covalent conjugation of antimicrobial peptides (AMP) has been one of the most widely used strategies by bioengineers, in an attempt to not only protect AMP from proteolytic degradation, but also to prolong their residence time at the target tissue. However, an explanation for the mode of action of conjugated AMP is still lacking. This review extensively gathers works on AMP conjugation and puts forward a mechanism of action for AMP when conjugated onto biomaterials. The implications of AMP conjugation on antimicrobial activity, cytotoxicity and resistance to proteases are all discussed. A thorough review of commonly employed chemical reactions for this conjugation is also provided. Finally, details that need to be addressed for conjugated AMP to reach clinical practice are discussed.

PET/CT and SPECT/CT for Infection in Joints and Bones: An Overview and Future Directions

Infections of the bones and joints, if misdiagnosed, may result in serious morbidity and even mortality. A prompt diagnosis followed by appropriate management may reduce the socioeconomic impact of bone and joint infections. Morphologic imaging such as ultrasound and plain radiographs form the first line investigations, however, in early infections findings may be negative or nonspecific. Nuclear medicine imaging techniques play a complementary role to morphologic imaging in the diagnosis of bone and joint infections. The availability of hybrid systems (SPECT/CT, SPECT/MRI, PET/CT or PET/MRI) offers improved specificity with ability to assess the extent of infection. Bone scans are useful as a gatekeeper wherein negative scans rule out sepsis with a good accuracy, however positive scans are nondiagnostic and more specific tracers should be considered. These include the use of labeled white blood cells and antigranulocyte antibodies. Various qualitative and quantitative interpretation criteria have been suggested to improve the specificity of the scans. PET has better image resolution and 18F-FDG is the major tracer for PET imaging with applications in oncology and inflammatory/infective disorders. It has demonstrated improved sensitivity over the SPECT based tracers, however, still suffers from lack of specificity. 18F-FDG PET has been used to monitor therapy in bone and joint infections. Other less studied, noncommercialized SPECT and PET tracers such as 111In-Biotin, 99mTc-Ubiquicidin, 18F-Na-Fluoride, 18F-labeled white blood cells and 124I-Fialuridine to name a few have shown great promise, however, their role in various bone and joint infections has not been established. Hybrid imaging with PET or PET/MRI offers huge potential for improving diagnostics in infections of the joints and bones.

Tryptophan End-Tagging Confers Antifungal Activity on a Tick-Derived Peptide by Triggering Reactive Oxygen Species Production

WHO has identified several Candida species including Candida albicans as critical priority fungal pathogens due to greater infection prevalence and formation of recalcitrant biofilms. Novel antifungal agents are urgently needed, and antimicrobial peptides (AMPs) are being considered as potential alternatives, but inactivity in physiological salt environments, serum, and plasma often limits further therapeutic development. Tryptophan end-tagging is a strategy to overcome these limitations and is thought to selectively enhance membrane permeabilization in both fungal and bacterial plasma membranes. Here, we show that C-terminal tryptophan end-tagging of the tick-derived peptide Os-C transforms an inactive peptide into Os-C(W5), an antifungal peptide capable of preventing the formation of C. albicans biofilms. Mechanistic insight is provided by circular dichroism spectroscopy and molecular dynamics simulations, which demonstrate that tryptophan end-tagging alters the secondary structure of Os-C, while the latter reveals that end-tagging reduces interactions with, and insertion into, a model C. albicans membrane but promotes peptide aggregation on its surface. Interestingly, this leads to the induction of reactive oxygen species production rather than membrane permeabilization, and consequently, oxidative stress leads to cell wall damage. Os-C(W5) does not induce the hemolysis of human erythrocytes. Reduced cell adhesion and viability contribute to decreased biofilm extracellular matrix formation which, although reduced, is retained in the serum-containing medium. In this study, tryptophan end-tagging was identified as a promising strategy for enhancing the antifungal activity, including the biofilm inhibitory activity of Os-C against C. albicans in physiological salt environments.

Influence of connatural factors in shaping vaginal microflora and ensuring its health

Vaginal canal (VC) is exposed to the external environment affected by habitual factors like hygiene and sexual behaviour as well as physiological factors like puberty, menstrual cycle, pregnancy, child birth and menopause. Healthy VC harbours beneficial microflora supported by vaginal epithelium and cervical fluid. Connatural antimicrobial peptide (AMPs) of female reproductive tract (FRT) conjunctly with these beneficial microbes provide protection from a large number of infectious diseases. Such infections may either be caused by native microbes of the VC or transitory microbes like bacteria or virus which are not a part of VC microflora. This review highlight's the role of hormones, enzymes, innate immunological factors, epithelial cells and vaginal mucus that support beneficial microbes over infectious ones thus, helping to maintain homeostasis in VC and further protect the FRT. We also discuss the prospective use of vaginal probiotics and AMPs against pathogens which can serve as a potential cure for vaginal infections.

Lipid vesicle-based molecular robots

A molecular robot, which is a system comprised of one or more molecular machines and computers, can execute sophisticated tasks in many fields that span from nanomedicine to green nanotechnology. The core parts of molecular robots are fairly consistent from system to system and always include (i) a body to encapsulate molecular machines, (ii) sensors to capture signals, (iii) computers to make decisions, and (iv) actuators to perform tasks. This review aims to provide an overview of approaches and considerations to develop molecular robots. We first introduce the basic technologies required for constructing the core parts of molecular robots, describe the recent progress towards achieving higher functionality, and subsequently discuss the current challenges and outlook. We also highlight the applications of molecular robots in sensing biomarkers, signal communications with living cells, and conversion of energy. Although molecular robots are still in their infancy, they will unquestionably initiate massive change in biomedical and environmental technology in the not too distant future.

Recent Advancements in Radiopharmaceuticals for Infection Imaging

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine, with its powerful scintigraphic, single photon emission computer tomography (SPECT), and positron emission tomography (PET) imaging modalities, has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals, there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled antifungals for fungal infections imaging, radiolabeled pathogen-specific antibodies, and molecular engineered constructs. In this chapter, we discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

Radiosynthesis Standardization and Preclinical Assessment of the [68Ga]Ga-DOTA-Ubiquicidin29-41: A Translational Study Targeting Differential Diagnosis of Infectious Processes

Human bacterial infections significantly contribute to the increase in healthcare-related burdens. This scenario drives the study of novel techniques for the early and precise diagnosis of infectious processes. Some alternatives include Nuclear Medicine- and Molecular Imaging-based strategies. However, radiopharmaceuticals that are available for routine assessments are not specific to differentiating infectious from aseptic inflammatory processes. In this context, [68Ga]Ga-DOTA-Ubiquicidin29-41 was synthesized using an automated module and radiochemical; in vivo and in vitro studies were performed. The radiopharmaceutical remained stable in saline (up to 180 min) and in rodent serum (up to 120 min) with radiochemical purities > 99 and 95%, respectively. Partition coefficient and serum protein binding at 60 min were determined (-3.63 ± 0.17 and 44.06 ± 1.88%, respectively). Ex vivo biodistribution, as well as in vivo microPET/CT images in mice, showed rapid blood clearance with renal excretion and reduced uptake in other organs in Staphylococcus aureus-infected animals. Higher uptake was observed in the target as compared to the non-target tissue (p < 0.0001) at 60 min post administration. The presented in-human clinical case demonstrates uptake of the radiopharmaceutical by Staphyloccocus aureus bacteria. These results indicate the potential of [68Ga]Ga-DOTA-Ubiquicidin29-41 as a radiopharmaceutical that can be obtained in a hospital radiopharmacy for the diagnosis of infectious processes using PET/CT.

Multi-label classification and features investigation of antimicrobial peptides with various functional classes

The challenge of drug-resistant bacteria to global public health has led to increased attention on antimicrobial peptides (AMPs) as a targeted therapeutic alternative with a lower risk of resistance. However, high production costs and limitations in functional class prediction have hindered progress in this field. In this study, we used multi-label classifiers with binary relevance and algorithm adaptation techniques to predict different functions of AMPs across a wide range of pathogen categories, including bacteria, mammalian cells, fungi, viruses, and cancer cells. Our classifiers attained promising AUC scores varying from 0.8492 to 0.9126 on independent testing data. Forward feature selection identified sequence order and charge as critical, with specific amino acids (C and E) as discriminative. These findings provide valuable insights for the design of antimicrobial peptides (AMPs) with multiple functionalities, thus contributing to the broader effort to combat drug-resistant pathogens.

The bactericidal and antibiofilm effects of a lysine-substituted hybrid peptide, CM-10K14K, on biofilm-forming Staphylococcus epidermidis

Staphylococci, notably biofilm-forming Staphylococcus epidermidis, have been recognized as global nosocomial pathogens in medical device-related infections. Their potential to attach to and form biofilm on indwelling catheters are significant factors impeding conventional treatment. Due to their extensive antimicrobial and antibiofilm actions, antimicrobial peptides (AMPs) have attracted interest as promising alternative compounds for curing difficult-to-treat, biofilm-forming bacterial infections. Cecropin A-melittin or CM, a well-known hybrid peptide, exhibits broad-spectrum antimicrobial activity, however it also possesses high toxicity. In the current study, a series of hybrid CM derivatives was designed using an amino acid substitution strategy to explore potential antibacterial and antibiofilm peptides with low toxicity. Among the derivatives, CM-10K14K showed the least hemolysis along with potent antibacterial activity against biofilm-forming S. epidermidis (MICs = 3.91 μg/mL) and rapid killing after 15 min exposure (MBCs = 7.81 μg/mL). It can prevent the formation of S. epidermidis biofilm and also exhibited a dose-dependent eradication activity on mature or established S. epidermidis biofilm. In addition, it decreased the development of biofilm by surviving bacteria, and formation of biofilm on the surface of CM-10K14K-impregnated catheters. Released CM-10K14K decreased planktonic bacterial growth and inhibited biofilm formation by S. epidermidis in a dose-dependent manner for 6 and 24 h post-exposure. Impregnation of CM-10K14K prevented bacterial attachment on catheters and thus decreased formation of extensive biofilms. SEM images supported the antibiofilm activity of CM-10K14K. Flow cytometry analysis and TEM images demonstrated a membrane-active mechanism of CM-10K14K, inducing depolarization and permeabilization, and subsequent membrane rupture leading to cell death. The presence of an interaction with bacterial DNA was verified by gel retardation assay. These antibacterial and antibiofilm activities of CM-10K14K suggest its potential application to urinary catheters for prevention of biofilm-forming colonization or for treatment of medical devices infected with S. epidermidis.

Antimicrobial Peptides as Immunomodulators and Antimycobacterial Agents to Combat Mycobacterium tuberculosis: a Critical Review

Tuberculosis (TB) is a devastating disease foisting a significantly high morbidity, prepotent in low- and middle-income developing countries. Evolution of drug resistance among Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, has made the TB treatment more complicated. The protracted nature of present TB treatment, persistent and tolerant Mtb populations, interaction with antiretroviral therapy and existing toxicity concerned with conventional anti-TB drugs are the four major challenges inflicted with emergence of drug-resistant mycobacterial strains, and the standard medications are unable to combat these strains. These factors emphasize an exigency to develop new drugs to overcome these barriers in current TB therapy. With this regard, antimycobacterial peptides derived from various sources such as human cells, bacterial sources, mycobacteriophages, fungal, plant and animal sources could be considered as antituberculosis leads as most of these peptides are associated with dual advantages of having both bactericidal activity towards Mtb as well as immuno-regulatory property. Some of the peptides possess the additional advantage of interacting synergistically with antituberculosis medications too, thereby increasing their efficiency, underscoring the vigour of antimicrobial peptides (AMPs) as best possible alternative therapeutic candidates or adjuvants in TB treatment. Albeit the beneficiary features of these peptides, few obstacles allied with them like cytotoxicity and proteolytic degradation are matter of concerns too. In this review, we have focused on structural hallmarks, targeting mechanisms and specific structural aspects contributing to antimycobacterial activity and discovered natural and synthetic antimycobacterial peptides along with their sources, anti-TB, immuno-regulatory properties, merits and demerits and possible delivery methods of AMPs.

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.

Antimicrobial activity, membrane interaction and structural features of short arginine-rich antimicrobial peptides

Antimicrobial activity of many AMPs can be improved by lysine-to-arginine substitution due to a more favourable interaction of arginine guanidinium moiety with bacterial membranes. In a previous work, the structural and functional characterization of an amphipathic antimicrobial peptide named RiLK1, including lysine and arginine as the positively charged amino acids in its sequence, was reported. Specifically, RiLK1 retained its β-sheet structure under a wide range of environmental conditions (temperature, pH, and ionic strength), and exhibited bactericidal activity against Gram-positive and Gram-negative bacteria and fungal pathogens with no evidence of toxicity on mammalian cells. To further elucidate the influence of a lysine-to-arginine replacement on RiLK1 conformational properties, antimicrobial activity and peptide-liposome interaction, a new RiLK1-derivative, named RiLK3, in which the lysine is replaced with an arginine residue, was projected and characterised in comparison with its parental compound. The results evidenced that lysine-to-arginine mutation not only did not assure an improvement in the antimicrobial potency of RiLK1 in terms of bactericidal, virucidal and fungicidal activities, but rather it was completely abolished against the hepatitis A virus. Therefore, RiLK1 exhibited a wide range of antimicrobial activity like other cationic peptides, although the exact mechanisms of action are not completely understood. Moreover, tryptophan fluorescence measurements confirmed that RiLK3 bound to negatively charged lipid vesicles with an affinity lower than that of RiLK1, although no substantial differences from the structural and self-assembled point of view were evidenced. Therefore, our findings imply that antimicrobial efficacy and selectivity are affected by several complex and interrelated factors related to substitution of lysine with arginine, such as their relative proportion and position. In this context, this study could provide a better rationalisation for the optimization of antimicrobial peptide sequences, paving the way for the development of novel AMPs with broad applications.

Preclinical Research Highlighting Contemporary Targeting Mechanisms of Radiolabelled Compounds for PET Based Infection Imaging

It is important to constantly monitor developments in the preclinical imaging arena of infection. Firstly, novel radiopharmaceuticals with the correct characteristics must be identified to funnel into the clinic. Secondly, it must be evaluated if enough innovative research is being done and adequate resources are geared towards the development of radiopharmaceuticals that could feed into the Nuclear Medicine Clinic in the near future. It is proposed that the ideal infection imaging agent will involve PET combined with CT but more ideally MRI. The radiopharmaceuticals currently presented in preclinical literature have a wide selection of vectors and targets. Ionic formulations of PET-radionuclides such 64CuCl2 and 68GaCl2 are evaluated for bacterial infection imaging. Many small molecule based radiopharmaceuticals are being investigated with the most prominent targets being cell wall synthesis, maltodextrin transport (such as [18F]F-maltotriose), siderophores (bacterial and fungal infections), the folate synthesis pathway (such as [18F]F-PABA) and protein synthesis (radiolabelled puromycin). Mycobacterial specific antibiotics, antifungals and antiviral agents are also under investigation as infection imaging agents. Peptide based radiopharmaceuticals are developed for bacterial, fungal and viral infections. The radiopharmaceutical development could even react quickly enough on a pandemic to develop a SARS-CoV-2 imaging agent in a timely fashion ([64Cu]Cu-NOTA-EK1). New immuno-PET agents for the imaging of viruses have recently been published, specifically for HIV persistence but also for SARS-CoV2. A very promising antifungal immuno-PET agent (hJ5F) is also considered. Future technologies could include the application of aptamers and bacteriophages and even going as far as the design of theranostic infection. Another possibility would be the application of nanobodies for immuno-PET applications. Standardization and optimization of the preclinical evaluation of radiopharmaceuticals could enhance clinical translation and reduce time spent in pursuing less than optimal candidates.

Bacillus licheniformis: A Producer of Antimicrobial Substances, including Antimycobacterials, Which Are Feasible for Medical Applications

Bacillus licheniformis produces several classes of antimicrobial substances, including bacteriocins, which are peptides or proteins with different structural composition and molecular mass: ribosomally synthesized by bacteria (1.4-20 kDa), non-ribosomally synthesized peptides and cyclic lipopeptides (0.8-42 kDa) and exopolysaccharides (>1000 kDa). Different bacteriocins act against Gram-positive or Gram-negative bacteria, fungal pathogens and amoeba cells. The main mechanisms of bacteriocin lytic activity include interaction of peptides with membranes of target cells resulting in structural alterations, pore-forming, and inhibition of cell wall biosynthesis. DNase and RNase activity for some bacteriocines are also postulated. Non-ribosomal peptides are synthesized by special non-ribosomal multimodular peptide synthetases and contain unnatural amino acids or fatty acids. Their harmful effect is due to their ability to form pores in biological membranes, destabilize lipid packaging, and disrupt the peptidoglycan layer. Lipopeptides, as biosurfactants, are able to destroy bacterial biofilms. Secreted polysaccharides are high molecular weight compounds, composed of repeated units of sugar moieties attached to a carrier lipid. Their antagonistic action was revealed in relation to bacteria, viruses, and fungi. Exopolysaccharides also inhibit the formation of biofilms by pathogenic bacteria and prevent their colonization on various surfaces. However, mechanism of the harmful effect for many secreted antibacterial substances remains unknown. The antimicrobial activity for most substances has been studied in vitro only, but some substances have been characterized in vivo and they have found practical applications in medicine and veterinary. The cyclic lipopeptides that have surfactant properties are used in some industries. In this review, special attention is paid to the antimycobacterials produced by B. licheniformis as a possible approach to combat multidrug-resistant and latent tuberculosis. In particular, licheniformins and bacitracins have shown strong antimycobacterial activity. However, the medical application of some antibacterials with promising in vitro antimycobacterial activity has been limited by their toxicity to animals and humans. As such, similar to the enhancement in the antimycobacterial activity of natural bacteriocins achieved using genetic engineering, the reduction in toxicity using the same approach appears feasible. The unique capability of B. licheniformis to synthesize and produce a range of different antibacterial compounds means that this organism can act as a natural universal vehicle for antibiotic substances in the form of probiotic cultures and strains to combat various types of pathogens, including mycobacteria.

Structure-Activity Relationship Study of Antimicrobial Peptide PE2 Delivered Novel Linear Derivatives with Potential of Eradicating Biofilms and Low Incidence of Drug Resistance

The ongoing emergence of antibiotic-resistant pathogens had been dramatically stimulating and accelerating the need for new drugs. PE2 is a kind of cyclic lipopeptide with broad-spectrum antimicrobial activity. Herein, its structure-activity relationship was systematically investigated by employing 4 cyclic analogues and 23 linear analogues for the first time. The screened linear analogues 26 and 27 bearing different fatty acyls at N-termini and a Tyr residue at the 9th position had superior potency compared to the cyclic analogues and showed equivalent antimicrobial activity compared with PE2. Notably, 26 and 27 exhibited significant ability against multidrug-resistant bacteria, favorable resistance to protease, excellent performance against biofilm, low drug resistance, and high effectiveness against the mice pneumonia model. The antibacterial mechanisms of PE2 and linear derivatives 26 and 27 were also preliminarily explored in this study. As described above, 26 and 27 are promising antimicrobial candidates for the treatment of infections associated with drug-resistant bacteria.

Biological Function of Antimicrobial Peptides on Suppressing Pathogens and Improving Host Immunity

The emergence of drug-resistant genes and concerns about food safety caused by the overuse of antibiotics are becoming increasingly prominent. There is an urgent need for effective alternatives to antibiotics in the fields of livestock production and human medicine. Antimicrobial peptides can effectively replace antibiotics to kill pathogens and enhance the immune functions of the host, and pathogens cannot easily produce genes that are resistant to them. The ability of antimicrobial peptides (AMPs) to kill pathogens is associated with their structure and physicochemical properties, such as their conformation, electrical charges, hydrophilicity, and hydrophobicity. AMPs regulate the activity of immunological cells and stimulate the secretion of inflammatory cytokines via the activation of the NF-κB and MAPK signaling pathways. However, there are still some limitations to the application of AMPs in the fields of livestock production and human medicine, including a restricted source base, high costs of purification and expression, and the instability of the intestines of animals and humans. This review summarizes the information on AMPs as effective antibiotic substitutes to improve the immunological functions of the host through suppressing pathogens and regulating inflammatory responses. Potential challenges for the commercial application of AMPs in animal husbandry and human medicine are discussed.

Assessing the Antimicrobial Properties of Honey Protein Components through In Silico Comparative Peptide Composition and Distribution Analysis

The availability of reference proteomes for two honeybee species (Apis mellifera and Apis cerana cerana) opens the possibility of in silico studies of diverse properties of the selected protein fractions. The antimicrobial activity of honey is well established and related to its composition, including protein components. We have performed a comparative study on a selected fraction of the honey-related proteins, as well as other bee-secreted proteins, utilizing a publicly available database of established and verified peptides with antimicrobial properties. Using a high-performance sequence aligner (diamond), protein components with antimicrobial peptide sequences were identified and analyzed. The identified peptides were mapped on the available bee proteome sequences, as well as on model structures provided by the AlphaFold project. The results indicate a highly conserved localization of the identified sequences within a limited number of the protein components. Putative antimicrobial fragments also show high sequence-based similarity to the multiple peptides contained in the reference databases. For the 2 databases used, the lowest calculated percentage of similarity ranged from 30.1% to 32.9%, with a respective average of 88.5% and 79.3% for the Apis mellifera proteome. It was revealed that the antimicrobial peptides (AMPs) site is a single, well-defined domain with potentially conserved structural features. In the case of the examples studied in detail, the structural domain takes the form of the two β-sheets, stabilized by α-helices in one case, and a six-β-sheet-only domain localized in the C-terminal part of the sequence, respectively. Moreover, no significant differences were found in the composition of the antibacterial fraction of peptides that were identified in the proteomes of both species.

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

Intracellular bacteria cause a wide range of diseases, and their intracellular lifestyle makes infections difficult to resolve. Furthermore, standard therapy antibiotics are often unable to eliminate the infection because they have poor cellular uptake and do not reach the concentrations needed to kill bacteria. In this context, antimicrobial peptides (AMPs) are a promising therapeutic approach. AMPs are short cationic peptides. They are essential components of the innate immune response and important candidates for therapy due to their bactericidal properties and ability to modulate host immune responses. AMPs control infections through their diverse immunomodulatory effects stimulating and/or boosting immune responses. This review focuses on AMPs described to treat intracellular bacterial infections and the known immune mechanisms they influence.

Current Status of SPECT Radiopharmaceuticals for Specific Bacteria Imaging

Imaging infection still represents a challenge for researchers. Despite nuclear medicine (NM) offers valuable tools able to discriminate between infections and inflammation, there is an unmet clinical need to develop new strategies able to specifically target the causative pathogen, to select the best antimicrobial treatment for each patient and to accurately assess therapeutic efficacy. These aspects are commonly addressed by microbiology or histology but the diagnosis often relies on invasive procedures that are prone to contamination or sample bias and do not reflect the spatial heterogeneity of the infective process. Therefore, in the era of personalized medicine and treatment, a lot of efforts are in play to improve a personalized diagnosis. Molecular imaging is an ideal candidate for this purpose and, indeed, research is going fast to this direction aiming to find more selective and proper antimicrobial treatments and to overcome broad-spectrum antibiotic use, which still represents the major cause of bacterial drug-resistance. Several approaches for specifically image bacteria have been proposed and provided encouraging perspectives in preclinical studies. Nevertheless, the majority of these promising approaches are still confined in "bench stages" and crucial issues still need to be addressed before their translation in clinical practice. This review will focus on radiolabeled antibiotics for SPECT imaging of bacteria, their mechanisms of action, their potentiality and limitations for "bed-side" applications.

Release of immunomodulatory peptides at bacterial membrane interfaces as a novel strategy to fight microorganisms

Cationic and amphiphilic peptides can be used as homing devices to accumulate conjugated antibiotics to bacteria-enriched sites and promote efficient microbial killing. However, just as important as tackling bacterial infections, is the modulation of the immune response in this complex microenvironment. In the present report, we designed a peptide chimaera called Chim2, formed by a membrane-active module, an enzyme hydrolysis site, and a formyl peptide receptor 2 (FPR2) agonist. This molecule was designed to adsorb onto bacterial membranes, promote their lysis, and upon hydrolysis by local enzymes, release the FPR2 agonist sequence for activation and recruitment of immune cells. We synthesized the isolated peptide modules of Chim2 and characterized their biological activities independently and as a single polypeptide chain. We conducted antimicrobial assays, along with other tests aiming at the analyses of the cellular and immunological responses. In addition, assays using vesicles as models of eukaryotic and prokaryotic membranes were conducted, and solution structures of Chim2 were generated by ¹H NMR. Chim2 is antimicrobial, adsorbs preferentially to negatively charged vesicles while adopting an α-helix structure, and exposes its disorganized tail to the solvent, which facilitates hydrolysis by tryptase-like enzymes, allowing the release of the FPR2 agonist fragment. This fragment was shown to induce accumulation of the cellular activation marker, lipid bodies, in mouse macrophages and the release of immunomodulatory interleukins. In conclusion, these data demonstrate that peptides with antimicrobial and immunomodulatory activities can be considered for further development as drugs.

Anti-Cancer Peptides: Status and Future Prospects

The dramatic rise in cancer incidence, alongside treatment deficiencies, has elevated cancer to the second-leading cause of death globally. The increasing morbidity and mortality of this disease can be traced back to a number of causes, including treatment-related side effects, drug resistance, inadequate curative treatment and tumor relapse. Recently, anti-cancer bioactive peptides (ACPs) have emerged as a potential therapeutic choice within the pharmaceutical arsenal due to their high penetration, specificity and fewer side effects. In this contribution, we present a general overview of the literature concerning the conformational structures, modes of action and membrane interaction mechanisms of ACPs, as well as provide recent examples of their successful employment as targeting ligands in cancer treatment. The use of ACPs as a diagnostic tool is summarized, and their advantages in these applications are highlighted. This review expounds on the main approaches for peptide synthesis along with their reconstruction and modification needed to enhance their therapeutic effect. Computational approaches that could predict therapeutic efficacy and suggest ACP candidates for experimental studies are discussed. Future research prospects in this rapidly expanding area are also offered.

Effect of charge on the antimicrobial activity of alpha-helical amphibian antimicrobial peptide

Antibiotic resistance is a severe threat to the world's public health, which has increased the need to discover novel antibacterial molecules. In this context, an emerging class of naturally occurring short peptide molecules called antimicrobial peptides (AMPs) has been considered potent antibacterial agents. Amphibians are one of the significant sources of AMPs, which have been extensively studied for the last few decades. Most amphibian AMPs are cationic, and several of these cationic AMPs adopt a well-defined alpha-helical structure in the presence of bacterial membranes. These cationic alpha-helical amphibian AMPs (CαAMPs) can selectively and preferentially bind with the negatively charged surfaces of Gram-positive and Gram-negative bacteria through electrostatic interaction, considered the main reason for their antibacterial activities. Here, we categorized these CαAMPs according to their charge, and to calculate the charge density; we divided the charge of each peptide by its corresponding length. To investigate the effect of charge among these categories, charge or charge density under each charge category was plotted against their corresponding minimum inhibitory concentration (MIC). Moreover, the effect of charge modification of some CαAMPs under specific charge categories in the context of MIC and hemolysis was also discussed. The information in this review will help us understand the antibacterial activity of accessible CαAMPs depending on each charge category across species. Additionally, this study suggests that designing novel functional antibacterial agents requires charge modification optimally.

A Novel Antimicrobial Peptide Sp-LECin with Broad-Spectrum Antimicrobial Activity and Anti-Pseudomonas aeruginosa Infection in Zebrafish

New antimicrobial agents are urgently needed to address the increasing emergence and dissemination of multidrug-resistant bacteria. In the study, a chemically synthesized truncated peptide containing 22-amino acids derived from a C-type lectin homolog SpCTL6 of Scylla paramamosain was screened and found to exhibit broad-spectrum antimicrobial activity, indicating that it is an antimicrobial peptide (AMP), named Sp-LECin. Sp-LECin possessed the basic characteristics of most cationic AMPs, such as positive charge (+4) and a relatively high hydrophobicity (45%). After treatment with Sp-LECin, the disruption of microbial membrane integrity and even leakage of cellular contents was observed by scanning electron microscopy (SEM). In addition, Sp-LECin could bind lipopolysaccharide (LPS), increase the outer and inner membrane permeability and induce reactive oxygen species (ROS) production, ultimately leading to the death of Pseudomonas aeruginosa. Furthermore, Sp-LECin exhibited potent anti-biofilm activity against P. aeruginosa during both biofilm formation and maturation. Notably, Sp-LECin had no obvious cytotoxicity and could greatly improve the survival of P. aeruginosa-infected zebrafish, by approximately 40% over the control group after 72 h of treatment. This study indicated that Sp-LECin is a promising antibacterial agent with the potential to be used against devastating global pathogen infections such as P. aeruginosa.

Membrane-Active Cyclic Amphiphilic Peptides: Broad-Spectrum Antibacterial Activity Alone and in Combination with Antibiotics

We designed a library of 24 cyclic peptides containing arginine (R) and tryptophan (W) residues in a sequential manner [R_nW_n] (n = 2-7) to study the impact of the hydrophilic/hydrophobic ratio, charge, and ring size on the antibacterial activity against Gram-positive and Gram-negative strains. Among peptides, 5a and 6a demonstrated the highest antimicrobial activity. In combination with 11 commercially available antibiotics, 5a and 6a showed remarkable synergism against a large panel of resistant pathogens. Hemolysis (HC₅₀ = 340 μg/mL) and cell viability against mammalian cells demonstrated the selective lethal action of 5a against bacteria over mammalian cells. Calcein dye leakage and scanning electron microscopy studies revealed the membranolytic effect of 5a. Moreover, the stability in human plasma (t_1/2 = 3 h) and the negligible ability of pathogens to develop resistance further reflect the potential of 5a for further development as a peptide-based antibiotic.

Antimicrobial and Cell-Penetrating Peptides: Understanding Penetration for the Design of Novel Conjugate Antibiotics

Antimicrobial peptides (AMPs) are short oligopeptides that can penetrate the bacterial inner and outer membranes. Together with cell-penetrating peptides (CPPs), they are called membrane active peptides; peptides which can translocate across biological membranes. Over the last fifty years, attempts have been made to understand the molecular features that drive the interactions of membranes with membrane active peptides. This review examines the features of a membrane these peptides exploit for translocation, as well as the physicochemical characteristics of membrane active peptides which are important for translocation. Moreover, it presents examples of how these features have been used in recent years to create conjugates consisting of a membrane active peptide, called a "vector", attached to either a current or novel antibiotic, called a "cargo" or "payload". In addition, the review discusses what properties may contribute to an ideal peptide vector able to deliver cargoes across the bacterial outer membrane as the rising issue of antimicrobial resistance demands new strategies to be employed to combat this global public health threat.

Fungicidal activity of human antimicrobial peptides and their synergistic interaction with common antifungals against multidrug-resistant Candida auris

Emergence of Candida auris, a multidrug-resistant yeast, demonstrates the urgent need for novel antifungal agents. Human antimicrobial peptides (AMPs) are naturally occurring molecules with wide spectrum antimicrobial activity, particularly against a variety of fungi. Therefore, this study examined the antifungal activity of seven different human AMPs against C. auris following the CLSI guidelines. The antifungal activity was further assessed using time kill curve and cell viability assays. For combination interaction, effectiveness of these peptides with three antifungals, fluconazole, amphotericin B, and caspofungin was done following standard protocols. To elucidate the antifungal mechanism, the effects of peptides on membrane permeability were investigated using propidium iodide staining method and confocal imaging. Antifungal susceptibility results showed that all the examined peptides possessed fungicidal effect against C. auris at different levels, with human β-defensin-3 being the most potent antifungal with MIC values ranging from 3.125 to 12.5 µg/ml. Time kill curves further confirmed the killing effect of all the tested peptides. Viability assay showed a significant decrease in the percentage of viable cells exposed to different inhibitory and fungicidal concentrations of each peptide (p < 0.01). Furthermore, peptides showed mostly synergistic interaction when combined with conventional antifungal drugs, with caspofungin showing 100% synergy when combined with different AMPs. As antifungal mechanism, peptides disrupted the membrane permeability at concentrations that correlated with the inhibition of growth. Overall, the findings of this study point towards the application of the tested peptides as a monotherapy or as a combination therapy with antifungal drugs to treat multidrug-resistant C. auris infections.

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

A Novel Cryptic Clostridial Peptide That Kills Bacteria by a Cell Membrane Permeabilization Mechanism

This work reports detailed characteristics of the antimicrobial peptide Intestinalin (P30), which is derived from the LysC enzyme of Clostridium intestinale strain URNW. The peptide shows a broader antibacterial spectrum than the parental enzyme, showing potent antimicrobial activity against clinical strains of Gram-positive staphylococci and Gram-negative pathogens and causing between 3.04 ± 0.12 log kill for Pseudomonas aeruginosa PAO1 and 7.10 ± 0.05 log kill for multidrug-resistant Acinetobacter baumannii KPD 581 at a 5 μM concentration. Moreover, Intestinalin (P30) prevents biofilm formation and destroys 24-h and 72-h biofilms formed by Acinetobacter baumannii CRAB KPD 205 (reduction levels of 4.28 and 2.62 log CFU/mL, respectively). The activity of Intestinalin is combined with both no cytotoxicity and little hemolytic effect against mammalian cells. The nuclear magnetic resonance and molecular dynamics (MD) data show a high tendency of Intestinalin to interact with the bacterial phospholipid cell membrane. Although positively charged, Intestinalin resides in the membrane and aggregates into small oligomers. Negatively charged phospholipids stabilize peptide oligomers to form water- and ion-permeable pores, disrupting the integrity of bacterial cell membranes. Experimental data showed that Intestinalin interacts with negatively charged lipoteichoic acid (logK based on isothermal titration calorimetry, 7.45 ± 0.44), causes membrane depolarization, and affects membrane integrity by forming large pores, all of which result in loss of bacterial viability. IMPORTANCE Antibiotic resistance is rising rapidly among pathogenic bacteria, becoming a global public health problem that threatens the effectiveness of therapies for many infectious diseases. In this respect, antimicrobial peptides appear to be an interesting alternative to combat bacterial pathogens. Here, we report the characteristics of an antimicrobial peptide (of 30 amino acids) derived from the clostridial LysC enzyme. The peptide showed killing activity against clinical strains of Gram-positive and Gram-negative pathogens. Experimental data and computational modeling showed that this peptide forms transmembrane pores, directly engaging the negatively charged phospholipids of the bacterial cell membrane. Consequently, dissipation of the electrochemical gradient across cell membranes affects many vital processes, such as ATP synthesis, motility, and transport of nutrients. This kind of dysfunction leads to the loss of bacterial viability. Our firm conviction is that the presented study will be a helpful resource in searching for novel antimicrobial peptides that could have the potential to replace conventional antibiotics.

Novel D-form of hybrid peptide (D-AP19) rapidly kills Acinetobacter baumannii while tolerating proteolytic enzymes

Antimicrobial peptides (AMPs) are being developed as potent alternative treatments to conventional antibiotics which are unlikely to induce bacterial resistance. They can be designed and modified to possess several druggable properties. We report herein a novel hybrid peptide of modified aurein (A3) and cathelicidin (P7), or A3P7, by a flipping technique. It exhibited potent antibacterial activity against both Gram-negative and -positive pathogenic bacteria but had moderate hemolytic activity. To reduce the sequence length and toxicity, C-terminal truncation was serially performed and eight truncated derivatives (AP12-AP19) were obtained. They had significantly less hemolytic activity while preserving antibacterial activity. Secondary structures of the candidate peptides in environments simulating bacterial membranes (30 mM SDS and 50% TFE), determined by CD spectroscopy, showed α-helical structures consistent with predicted in silico 3D structural models. Among the peptides, AP19 demonstrated the best combination of broad-spectrum antibacterial activity (including toward Acinetobacter baumannii) and minimal hemolytic and cytotoxic activities. A D-form peptide (D-AP19), in which all L-enantiomers were substituted with the D-enantiomers, maintained antibacterial activity in the presence of pepsin, trypsin, proteinase K and human plasma. Both isomers exhibited potent antibacterial activity against multi-drug (MDR) and extensively-drug resistant (XDR) clinical isolates of A. baumannii comparable to the traditional antibiotic, meropenem. D-AP19 displayed rapid killing via membrane disruption and leakage of intracellular contents. Additionally, it showed a low tendency to induce bacterial resistance. Our work suggested that D-AP19 could be further optimized and developed as a novel compound potentially for fighting against MDR or XDR A. baumannii.

Role of Antimicrobial Peptides in Treatment and Prevention of Mycobacterium Tuberculosis: A Review

Tuberculosis (TB) is one of the leading cause of death worldwide, and the world is fighting with this global health emergency from the past 25 year. The current clinical interventions for the management of TB face a number of inherent challenges which includes low patient compliance due to the long therapy regimen, and emerging antimicrobial resistance. Therefore, there is an unmet need of new anti-TB therapeutic agent with enhanced safety profile, which can reduce the duration of therapy, enhanced bioavailability and efficacy against drug resistant forms of TB. Bacteriocins or anti microbial peptides (AMPs) occurring in microbes, human beings and other life forms have been investigated as host defense peptides. Structurally AMPs are short and ionized and play crucial role in innate immunity of host. Some AMPs can kill microbial infections directly while others function indirectly by altering the host defense mechanisms. Amidst rising issue of antibiotic resistance, AMPs are being tested in clinical research as potential antibiotics and novel therapeutics to fight against infections and non-infectious diseases. Studies have also highlighted the ability of AMPs to act against the bacteria spreading tuberculosis. The present review provides information on antimicrobial peptides, highlights their biological role, classification and mode of action in treatment and prevention of tuberculosis. It further mentions the prospects and challenges of developing peptides for their therapeutic applications against mycobacterium tuberculosis.

The dual interaction of antimicrobial peptides on bacteria and cancer cells; mechanism of action and therapeutic strategies of nanostructures

Microbial infection and cancer are two leading causes of global mortality. Discovering and developing new therapeutics with better specificity having minimal side-effects and no drug resistance are of an immense need. In this regard, cationic antimicrobial peptides (AMP) with dual antimicrobial and anticancer activities are the ultimate choice. For better efficacy and improved stability, the AMPs available for treatment still required to be modified. There are several strategies in which AMPs can be enhanced through, for instance, nano-carrier application with high selectivity and specificity enables researchers to estimate the rate of drug delivery to a particular tissue. In this review we present the biology and modes of action of AMPs for both anticancer and antimicrobial activities as well as some modification strategies to improve the efficacy and selectivity of these AMPs.

Membrane disruptive action of cationic anti-bacterial peptide B1CTcu3

A twenty-two-residue peptide Brevinin1 Clinotarsus curtipus-3 (B1CTcu3), identified from the skin secretion of frog Clinotarsus curtipes of the Western Ghats, exhibited a broad range of antibacterial activity against Gram-negative and Gram-positive bacteria, including the methicillin-resistant Staphylococcus aureus (MRSA). It showed anti-biofilm activity even at sub-Minimum Inhibitory Concentration (sub-MIC) against Pseudomonas aeruginosa and Staphylococcus aureus. Analysis of the scanning electron microscopic (SEM) images, confocal images, flow cytometric data and the effect of salt concentration on antibacterial potency suggests that the killing action of the peptide is through the membranolytic process. Single channel electric recording confirmed that the peptide elicited pores on the bacterial cell membrane as it induces a heterogeneous channel in the lipid bilayer.  It also showed cytotoxicity against MDA-MB-231 breast cancer cell with IC50 of 25µM. B1CTcu3 peptide could serve as the template for next-generation antibacterial agents, particularly against antibiotic resistant pathogenic bacteria.

Prediction and characterization of a novel hemoglobin-derived mutant peptide (mTgHbP7) from Tegillarca granosa

The hemoglobin (Hb) is identified in Tegillarca granosa and its derived peptides have been proved to possess antibacterial activity against gram-positive and gram-negative bacteria. In this study, we identified a series of novel antimicrobial peptides (AMPs) and artificially mutated AMPs derived from subunits of T. granosa Hbs, among which, a mutant T. granosa hemoglobin peptide (mTgHbP) mTgHbP7, was proved to possess predominant antibacterial activity against three bacteria strains (Vibrio alginolyticus, V. parahaemolyticus and Escherichia coli). Besides, mTgHbP7 was predicted to form α-helical structure, which was known to be an important feature of bactericidal AMPs. Furthermore, upon contact with HEK293 cell line, we confirmed that mTgHbP7 had no cytotoxicity to mammalian cell even at a high concentration of 160 μM. Therefore, the findings reported here provide a rationalization for antimicrobial peptide prediction and optimization from mollusk hemoglobin, which will be useful for future development of antimicrobial agents.

Effect of biphosphate salt on dipalmitoylphosphatidylcholine bilayer deformation by Tat polypeptide

Translocation of positively charged cell penetrating peptides (CPP) through cell membrane is important in drug delivery. Here we report all-atom molecular dynamics simulations to investigate how a biphosphate salt in a solvent affects the interaction of a CPP, HIV-1 Tat peptide with model dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Tat peptide has a large number of basic arginines and a couple of polar glutamines. We observe that in absence of salt, the basic residues of the polypeptide get localized in the vicinity of the membrane without altering the bilayer properties much; polypeptide induce local thinning of the bilayer membrane at the area of localization. In presence of biphosphate salt, the basic residues, dressed by the biphosphate ions, are repelled by the phosphate head groups of the lipid molecules. However, polar glutamine prefers to stay in the vicinity of the bilayer. This leads to larger local bilayer thickness at the contact point by the polar residue and non-uniform bilayer thickness profile. The thickness deformation of bilayer structure disappears upon mutating the polar residue, suggesting importance of the polar residue in bilayer deformation. Our studies point to control bilayer deformation by appropriate peptide sequence and solvent conditions.

Highlights of the Latest Developments in Radiopharmaceuticals for Infection Imaging and Future Perspectives

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine with its powerful scintigraphic, single photon emission computer tomography (SPECT) and positron emission tomography (PET) imaging modalities has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled anti-fungals for fungal infections imaging, radiolabeled pathogen-specific antibodies and molecular engineered constructs. In this opinion piece, we would like to discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections in order to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

The characteristics and roles of antimicrobial peptides as potential treatment for antibiotic-resistant pathogens: a review

The emergence of antibiotic-resistant bacteria has become a significant and ever-increasing threat to global public health, increasing both morbidity and mortality rates, and the financial burden on health services. Infection by drug-resistant bacteria is anticipated to contribute to the demise of almost 10 million people by the year 2050 unless a competent and effective response is devised to engage with this issue. The emergence and spread of resistance are commonly caused by the excessive or inappropriate use of antibiotics and substandard pharmaceuticals. It arises when pathogens adapt to different conditions and develop self-defence mechanisms. Currently, novel antimicrobial peptides (AMPs) have been reported to be the sole cure for some clinical cases of infectious diseases such as sepsis and skin infections, although these agents may, on occasion, require administration together with an adjunctive low-dose antibiotic. Although AMPs are a promising alternative form of anti-microbial therapy and easily applied in the medical sector, they still have limitations that should not be taken lightly. Hence, this review explores the characteristics, advantages and disadvantages of AMPs for their potential in treating antibiotic-resistant pathogens.

Antibacterial and antioxidant activity of royal jelly collected from geographical regions with different climates in the north of Iran

Royal jelly is one of the most important bee products. The biological activities of royal jelly can be influenced by various factors such as geographic origin, climatic conditions, vegetation. This study was carried out to evaluate the antibacterial and antioxidant activity of royal jelly samples collected from beehives from different geographical regions including mountain, coastal and plain regions in northern Iran. Antibacterial activity of royal jelly samples against ten bacteria was determined using agar well diffusion method. The MIC and MBC of royal jelly samples were determined by the broth microdilution method. Folin-Ciocâlteu reagent and reaction with DPPH were used to determine the total phenolic content and antioxidant potential of royal jelly samples, respectively. The MIC of samples ranged from 0.78 to 12.5% and MBC - from 3.12 to 50%. Samples collected from mountain regions showed the highest antibacterial activity with MIC for Gram-positive bacteria from 0.78 to 1.56% and for Gram-negative bacteria: from 1.56 to 3.12%. The total phenolic content and DPPH radical scavenging activity in royal jelly samples of the mountain region was significantly higher than those from the two regions with other climates. The results of this study indicated that the climate of the geographic region of sampling location had an effect on the antibacterial and antioxidant activity of royal jelly which may be due to differences in plant vegetation and the origin of the flowers of bees.

OUP accepted manuscript

Organismal survival depends on a well-balanced immune system and maintenance of host–microbe mutualism. The fine-tuned relationship between the gut microbiota and host immunity is constantly challenged by opportunistic bacteria testing the integrity of gastrointestinal (GI) barrier defenses. Barrier dysfunction reduces immunological tolerance towards otherwise innocuous microbes; it is a process that may instigate chronic inflammation. Paradoxically, sustained inflammation further diminishes barrier function, enabling bacterial translocation to extra-intestinal tissues. Once translocated, these bacteria stimulate systemic inflammation, thereby compromising organ function. While genetic risk alleles associate with barrier dysfunction, environmental stressors are key triggers of GI inflammation and associated breakdown in immune tolerance towards resident gut microbes. As dietary components dictate substrate availability, they also orchestrate microbiota composition and function, including migratory and pro-inflammatory potential, thus holding the capacity to fuel both GI and extra-intestinal inflammation. Additionally, Western diet consumption may weaken barrier defenses via curbed Paneth cell function and diminished host-defense peptide secretion. This review focuses on intervenable niches of host–microbe interactions and mucosal immunity with the ambition to provide a framework of plausible strategies to improve barrier function and regain tolerance in the inflamed mucosa via nutritional intervention.

Atomic force spectroscopy with magainin 1 functionalized tips and biomimetic supported lipid membranes

Antimicrobial peptides are molecules synthesized by living organisms as the first line of defense against bacteria, fungi, parasites, or viruses. Since their biological activity is based on destabilization of the microbial membranes, a study of direct interaction forces between antimicrobial peptides and biomimetic membranes is very important for understanding the molecular mechanisms of their action. Herein, we use atomic force spectroscopy to probe the interaction between atomic force microscopy (AFM) tips functionalized with magainin 1 and supported lipid bilayers (SLBs) mimicking electrically uncharged membranes of normal eukaryotic cells and negatively charged membranes of bacterial cells. The investigations performed on negatively charged SLBs showed that the magainin 1 functionalized AFM tips are quickly adsorbed into the SLBs when they approach, while they adhere strongly to the lipid membrane when retracted. On contrary, same investigations performed on neutral SLBs showed mechanical resistance of the lipid membrane to the tip breakthrough and negligible adhesion force at detachment.

Prospects of Exploring the Metal-Organic Framework for Combating Antimicrobial Resistance

Infectious diseases are a major public health concern globally. Infections caused by pathogens with resistance against commonly used antimicrobial drugs or antibiotics (known as antimicrobial resistance, AMR) are becoming extremely difficult to control. AMR has thus been declared as one of the top 10 global public health threats, as it has very limited solutions. The drying pipeline of effective antibiotics has further worsened the situation. There is no absolute treatment, and the limitations of existing methods warrant further development in antimicrobials. Recent developments in the nanomaterial field present them as promising therapeutics and effective alternative to conventional antibiotics and synthetic drugs. The metal-organic framework (MOF) is a recent addition to the antimicrobial category with superior properties. The MOF exerts antimicrobial action on a wide range of species and is highly biocompatible. Additionally, their porous structures allow the incorporation of biomolecules and drugs for synergistic antimicrobial action. This review provides an inclusive summary of the molecular events responsible for resistance development and current trends in antimicrobials to combat antibiotic resistance and explores the potential role of the MOF in tackling the drug-resistant microbial species.

Evaluation of 68Ga-DOTA-Ubiquicidin (29-41) for imaging Staphylococcus aureus (Staph A) infection and turpentine-induced inflammation in a preclinical setting

Synthetic antimicrobial peptide fragment, ^99mTc-Ubiquicidin 29–41, is shown to be sensitive and also specific for imaging bacterial infections. We undertook this study to explore the advantage of using a positron emission agent, ⁶⁸Ga-DOTA-Ubiquicidin 29–41 (⁶⁸Ga-DOTA-UBI), for detecting Staph-A infection in an animal model, and also evaluated its ability to distinguish a turpentine-induced sterile inflammation in an animal model. Pure Ga-68 was freshly eluted from a ⁶⁸Ge/⁶⁸Ga generator (IGG-100). DOTA-UBI (50 μg) was ra diolabeled with pure Ga-68 (500MBq) by incubating the reaction mixture at pH 4.5 for 10 min, 95°C. Rats were infected with Staph-A at the hind leg joint of rats to form bacterial abscess. Sterile inflammation was induced in the right thigh muscle by injecting 200 μl of 100% turpentine oil. Rats were injected intravenously with 10–15 MBq of tracer, and images were acquired at different time intervals with Siemens (Biograph mCT) positron emission tomography computed tomography scanner. The early images at 6 min postinjection clearly indicated mild uptake of the agent corresponding to the infection site, which increased dramatically at 20, 30, and 60 min postinjection. The target to background ratio (T/B) increased significantly over the same time period of study (1.6, 4.2, and 6.1, respectively). There was a mild uptake of ⁶⁸Ga-DOTA-UBI at the site corresponding to sterile inflammation at 6 min postinjection, which was rapidly washed off as seen at 25 and 45 min images. The images indicated fast clearance of the agent from liver and soft tissues within 6 min. Control rats showed similar biodistribution of activity. The mild uptake of ⁶⁸Ga-DOTA-UBI at the corresponding Staph-A infection lesion and very fast kinetics of clearance from the blood pool and soft tissues suggested a very high clinical potential for this agent. The absence of uptake of the agent at sterile inflammation site suggests that the agent may be useful in distinguishing infection from inflammation.

Virus-inspired designs of antimicrobial nanocapsules

Antimicrobial resistance is becoming a serious burden for drug design. The challenges are in finding novel approaches for effectively targeting a number of different bacterial strains, and in delivering these to the site of action. We propose here a novel approach that exploits the assembly of antimicrobial peptidic units in nanocapsules that can penetrate and rupture the bacterial membrane. Additionally, the chemical versatility of the designed units can be tailored to specific targets and to the delivery of genetic material in the cell. The proposed design exploits a β-annulus (sequence ITHVGGVGGSIMAPVAVSRQLVGS) triskelion unit from the Tomato Bushy Stunt Virus, able to self assemble in solution, and functionalised with antimicrobial sequences to form dodecahedral antimicrobial nanocapsules. The stability and the activity of the antimicrobial β-annulus capsule is measured by molecular dynamics simulations in water and in the presence of model membranes.

Antimicrobial Peptides and Their Applications in Biomedical Sector

In a report by WHO (2014), it was stated that antimicrobial resistance is an arising challenge that needs to be resolved. This resistance is a critical issue in terms of disease or infection treatment and is usually caused due to mutation, gene transfer, long-term usage or inadequate use of antimicrobials, survival of microbes after consumption of antimicrobials, and the presence of antimicrobials in agricultural feeds. One of the solutions to this problem is antimicrobial peptides (AMPs), which are ubiquitously present in the environment. These peptides are of concern due to their special mode of action against a wide spectrum of infections and health-related problems. The biomedical field has the highest need of AMPs as it possesses prominent desirable activity against HIV-1, skin cancer, breast cancer, in Behcet's disease treatment, as well as in reducing the release of inflammatory cells such as TNFα, IL-8, and IL-1β, enhancing the production of anti-inflammatory cytokines such as IL-10 and GM-CSF, and in wound healing properties. This review has highlighted all the major functions and applications of AMPs in the biomedical field and concludes the future potential of AMPs.

Bacterial-Specific Aggregation and Killing of Immunomodulatory Host Defense Peptides

This study involves the design and development of disulfide bridge-linked antimicrobial peptides using the host defense protein Angiogenin 4 (chAng4) as a template. The mini peptides derived from chAng4 (mCA4s) were evaluated for their antibacterial efficacies in various pathogenic bacterial strains, and the role of the oxidation state of thiols in the peptide sequence and its implication on antibacterial properties were explored. A remarkable property of these synthetic mCA4 peptides is their capability to flocculate bacteria and mediate bacterial-specific killing, in the absence of any other external stimulus. mCA4s were further evaluated for their cellular uptake, hemolytic activities, toxicities, and immunomodulatory activities in different eukaryotic cell lines. The results indicate that disulfide bridge-containing cationic amphipathic peptides show superior antibacterial efficacies, are nontoxic and nonhemolytic, and mediate bacterial flocculation and killing, in the absence of external stimuli.