Functional and structural insights on self-assembled nanofiber-based novel antibacterial ointment from antimicrobial peptides, bacitracin and gramicidin S

Anti-MRSA activity of chlorophenyl pyrrolo benzodiazepines compound

Antibiotic resistant is the major concern in public health to control the infectious diseases. MRSA (Methicillin-resistant Staphylococcus aureus) is a significant concern in healthcare settings due to its resistance to many antibiotics, including methicillin and other beta-lactams. MRSA infection difficult to treat and increases the risk of complications. Here, we have tested a series of highly condensed heterocyclic derivatives of pyrrolo[1,2-a][1,4]benzodiazepines. Compounds were tested against both, Gram-positive bacteria, Staphylococcus aureus and S. epidermidis, and Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, to assess the antimicrobial efficacy. Compared to Gram-negative bacteria, compounds showed much stronger antibacterial activity against Gram-positive bacteria. SM-5 [Ethyl2-(7-(4-chlorophenyl)-4-methoxy-6,7,8,13-tetrahydro-5H-benzo[e]benzo[5,6][1,4]diazepino[2,1-a]isoindol-15-yl)acetate] derivative was selected as best on the basis of higher therapeutic index among the tested compounds, showed MIC value of 7.81 µg. ml-1 against Staphylococcus strains. Molecular docking analysis between cell wall biosynthesis protein of S. aureus and SM-5 revealed that PBP2a showed the highest binding energy (-8.3 Kcal mol-1), followed by beta-lactam-inducible PBP4 (-7.7 Kcal mol-1), and lipoteichoic acid synthase (-7.5 Kcal mol-1) which is comparably higher than methicillin. Ground state energy calculations by DFT analysis revealed that compound SM-5 and SM-6, almost have equal electronegativity 0.11018 au which also satisfy the quality of the compound reactivity. Analysis of their biofilm inhibition in vitro and in silico toxicity analysis demonstrated their substantial potential to be a kind of future lead antibiotic.

A review of microbes mediated biosynthesis of silver nanoparticles and their enhanced antimicrobial activities

In recent decades, biosynthesis of metal and (or) metal oxide nanoparticles using microbes is accepted as one of the most sustainable, cost-effective, robust, and green processes as it does not encompass the usage of largely hazardous chemicals. Accordingly, numerous simple, inexpensive, and environmentally friendly approaches for the biosynthesis of silver nanoparticles (AgNPs) were reported using microbes avoiding conventional (chemical) methods. This comprehensive review detailed an advance made in recent years in the microbes-mediated biosynthesis of AgNPs and evaluation of their antimicrobial activities covering the literature from 2015-till date. It also aimed at elaborating the possible effect of the different phytochemicals, their concentrations, extraction temperature, extraction solvent, pH, reaction time, reaction temperature, and concentration of precursor on the shape, size, and stability of the synthesized AgNPs. In addition, while trying to understand the antimicrobial activities against targeted pathogenic microbes the probable mechanism of the interaction of produced AgNPs with the cell wall of targeted microbes that led to the cell's reputed and death have also been detailed. Lastly, this review detailed the shape and size-dependent antimicrobial activities of the microbes-mediated AgNPs and their enhanced antimicrobial activities by synergetic interaction with known commercially available antibiotic drugs.

Structural Organization of Brevilaterin Biosynthesis in Brevibacillus laterosporus S62-9: A Novel MbtH-Independent Cationic Antimicrobial Peptide Synthetase System

Cationic antimicrobial peptides, produced by nonribosomal peptide synthetases (NRPSs), have received great attention in different applications, including as biocontrol and antimicrobial agents against foodborne pathogenic bacteria. Also, Brevibacillus spp. is a competent microorganism to produce cationic antimicrobial peptides yet has received little attention. Herein, Brevibacillus laterosporus S62-9 genome mining revealed an integrated cationic antimicrobial peptide synthetase system that synthesized brevilaterin. Combining biochemical analysis with bioinformatics elucidated that the A domain from this system was the MbtH-independent enzyme and showed activity against the same amino acid in the structure of brevilaterin. Moreover, the creations of the first three and position 12 residues in the sequence were targeted to bre261, bre270, bre2691A, and bre2662, respectively. Further analysis of the specificity-conferring code of the A domain suggested that a tiny difference would make the activity of the A domain very diverse and the range of substrate selection would be enlarged or narrowed by changing some residues in the code. The dissection of this biosynthesis mechanism would contribute to the successful realization of reasonable artificial design and the modification of bioactive peptides, and this capable organism also would be more fully utilized.

Recent Advances and Mechanistic Insights into Antibacterial Activity, Antibiofilm Activity, and Cytotoxicity of Silver Nanoparticles

The substantial increase in multidrug-resistant (MDR) pathogenic bacteria is a major threat to global health. Recently, the Centers for Disease Control and Prevention reported possibilities of greater deaths due to bacterial infections than cancer. Nanomaterials, especially small-sized (size ≤10 nm) silver nanoparticles (AgNPs), can be employed to combat these deadly bacterial diseases. However, high reactivity, instability, susceptibility to fast oxidation, and cytotoxicity remain crucial shortcomings for their uptake and clinical application. In this review, we discuss various AgNPs-based approaches to eradicate bacterial infections and provide comprehensive mechanistic insights and recent advances in antibacterial activity, antibiofilm activity, and cytotoxicity (both in vitro and in vivo) of AgNPs. The mechanistic of antimicrobial activity involves four steps: (i) adhesion of AgNPs to cell wall/membrane and its disruption; (ii) intracellular penetration and damage; (iii) oxidative stress; and (iv) modulation of signal transduction pathways. Numerous factors affecting the bactericidal activity of AgNPs such as shape, size, crystallinity, pH, and surface coating/charge have also been described in detail. The review also sheds light on antimicrobial photodynamic therapy and the role of AgNPs versus Ag⁺ ions release in bactericidal activities. In addition, different methods of synthesis of AgNPs have been discussed in brief.

Bacitracin-Ag Nanoclusters as a Novel Antibacterial Agent Combats Shigella flexneri by Disrupting Cell Membrane and Inhibiting Biofilm Formation

A novel nanomaterial Bacitracin-Ag Nanoclusters (Bacitracin-AgNCs) was formed to achieve a better antibacterial effect on Shigella flexneri which poses a serious threat to human health. In the current study, X-ray photoelectron spectrometer (XPS), Fourier transform infrared (FTIR), field-emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HR-TEM) and thermal gravimetric analysis (TGA) were used to characterize the properties of composited Bacitracin-AgNCs. Furthermore, the inhibitory effects of Bacitracin-AgNCs against S. flexneri were explored, and the inhibition mechanism was discussed in terms of its aspects of cell membrane ravage, ATPase activity decline and biofilm inhibition. The results reveal that the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Bacitracin-AgNCs against S. flexneri were 0.03 mg/mL and 4 mg/mL. Bacitracin-AgNCs may cause irreversible impairment to cells and greatly change the cell morphology. The cell membrane integrity of S. flexneri was destroyed with changes in the characteristics of membrane permeability and intracellular substances leakage. Moreover, our study further proved that Bacitracin-AgNCs significantly inhibited the formation of S. flexneri biofilms and reduced the number of viable bacteria in biofilm. These findings provide a potential method for the exploitation of organic composite nanomaterials as a novel antimicrobial agent and its application in the food industry.

Nanofibers as drug-delivery systems for antimicrobial peptides

Microbial infections are a major worldwide public health problem because a number of microorganisms can show drug resistance. Antimicrobial peptides (AMPs) are small biomolecules that present antimicrobial and immunomodulatory activities. Despite their great potential, there are still many barriers to the formulation of these molecules. In this context, nanotechnological approaches such as nanofibers are candidate drug-delivery systems for AMP formulations. These nanomaterials have a large contact surface and may carry several AMPs (single or multilayer), directing them to specific targets. Thus, this review describes the main advances related to the use of nanofibers as drug-delivery systems for AMPs. These strategies can contribute directly to the design of new multifunctional wound dressings, coatings for prostheses, and tissue engineering applications.

Hierarchical Assembly of Nanodimensional Silver-Silver Oxide Physical Gels Controlling Nosocomial Infections

Microbial infections originating from medical care facilities are raising serious concerns across the globe. Therefore, nanotechnology-derived nanostructures have been investigated and explored due to their promising characteristics. In view of this, silver-based antimicrobial hydrogels as an alternative to antibiotic-based creams could play a crucial role in combating such infections. Toward this goal, we report a simple method for the synthesis and assembly of silver nanoparticles in a biopolymer physical gel derived from Abroma augusta plant in imparting antimicrobial properties against nosocomial pathogens. Synthesized silver nanoparticles (diameter, 30 ± 10 nm) were uniformly distributed inside the hydrogel. Such synthesized hydrogel assembly of silver nanoparticles dispersed in the biopolymer matrix exhibited hemocompatibility and antimicrobial and antibiofilm characteristics against nosocomial pathogens. The developed hydrogel as a surface coating offers reduced hardness and modulus value, thereby minimizing the brittleness tendency of the gel in the dried state. Hence, we believe that the hierarchical assembly of our hydrogel owing to its functional activity, host toxicity, and stability could possibly be used as an antimicrobial ointment for bacterial infection control.

Biosynthesis of AgNPs onto the urea-based periodic mesoporous organosilica (AgxNPs/Ur-PMO) for antibacterial and cell viability assay

Nano-size silver particles were stabilized on the inner surfaces of urea based periodic mesoporous organosilica (Ur-PMO). Aqueous extract of Euphorbia leaves as a sustainable and green reducing agent was applied for Ag-nanoparticles growth into the Ur-PMO channels. Physical and chemical properties of organosilica materials synthesized using various techniques such as FT-IR, small-angle XRD, PXRD, FESEM, TEM, SEM-EDX and atomic absorption spectrometry (AAS) were examined. Finally, the AgNPs/Ur-PMO were investigated on cell viability assay. An in vitro cytotoxicity test using MMT assay displayed that the designed material has good biocompatibility and could be a promising candidate for biomedical applications. The results also showed that the AgNPs/Ur-PMO compounds (especially, PMO; 1.27% AgNPs) had relatively good antibacterial and antibiofilm effects. It seems that the use of these compounds in hospital environments can reduce nosocomial infections as well as reduce antibiotic-resistant bacteria.

Inhaler with electrostatic sterilizer and use of cationic amphiphilic peptides may accelerate recovery from COVID-19

We explore the design of a smart inhaler with electrostatic sterilizer and propose the utilization of cationic amphiphilic peptides, independently or in conjunction with a bronchodilator, for COVID-19 patients to quickly improve wellbeing while maintaining a strategic distance to protect healthcare personnel from virus-containing aerosol or droplets during the process of inhalation.

d-Amino acids in antimicrobial peptides: a potential approach to treat and combat antimicrobial resistance

Antimicrobial resistance is one of the leading challenges in the human healthcare segment. Advances in antimicrobial resistance have triggered exploration of natural alternatives to stabilize its seriousness. Antimicrobial peptides are small, positively charged oligopeptides that are as potent as commercially available antibiotics against a wide spectrum of organisms, such as Gram-positive bacteria, Gram-negative bacteria, viruses, and fungal strains. In addition to their antibiotic capabilities, these peptides possess anticancer activity, activate the immune response, and regulate inflammation. Peptides have distinct modes of action and fall into various categories due to their amino acid composition. Although antimicrobial peptides specifically target the bacterial cytoplasmic membrane, they can also target the cell nucleus and protein synthesis. Owing to the increasing demand for novel treatments against the threat of antimicrobial resistance, naturally synthesized peptides are a beneficial development concept. Antimicrobial peptides are pervasive and can easily be modified using de-novo synthesis technology. Antimicrobial peptides can be isolated from natural resources such as humans, plants, bacteria, and fungi. This review gives a brief overview of antimicrobial peptides and their diastereomeric composition. Other current trends, the future scope of antimicrobial peptides, and the role of d-amino acids are also discussed, with a specific emphasis on the design and development of new drugs.

Antimicrobial peptide selection from Lippia spp leaf transcriptomes

Antimicrobial resistance is considered a health issue worldwide. This public health problem underscores the importance of searching for new antimicrobial molecules with different mechanisms of action. Leaf transcriptomes were used to search and develop synthetic antimicrobial peptides derived from mRNA sequences. The in silico search for new AMPs from the L. rotundifolia and L. alba transcriptomes allowed the identification of 120 putative peptide mRNA sequences. Eight of them fitted into optimal parameters and were translated and chemically synthesized antimicrobial peptides. Their biological activity was tested in both Gram-positive and Gram-negative bacteria against which they exhibited antibacterial activity. However, they showed an important hemolytic effect. Afterwards, two active peptides showing bactericidal activity isolated from each plant transcriptome tested were modified and modeled in 11 new variants to increase their antimicrobial activity and stability and to reduce or eliminate their hemolytic effect from their original peptides. The La-AMP1 (MSLLERKLLMHFLRV) the original peptide from L. alba showed a 52% hemolytic effect while the derived peptide La-AMP1a (GLMKLLRELLHMFSRVG) had its hemolytic effect reduced to 0.5% at 128 μg.mL^-1. Similarly, we observed that the original peptide from L. rotundifolia, Lr-AMP1 (MRIGLRFVLM), displayed a 71.5% hemolytic effect, while its derived peptide Lr-AMP1f (GSVLRAIMRMFAKLMG) showed 0% hemolysis at 128 μg.mL^-1, tested with fresh human erythrocytes. Our results indicate a promising method for the search for novel antimicrobial agents with reduced or zero hemolytic effect, as well as prediction and optimization of their activity from plant mRNA libraries.

Topical antimicrobial peptide formulations for wound healing: Current developments and future prospects

Antimicrobial peptides (AMPs) are the natural antibiotics recognized for their potent antibacterial and wound healing properties. Bare AMPs have limited activity following topical application attributable to their susceptibility to environment (hydrolysis, oxidation, photolysis), and wound (alkaline pH, proteolysis) related factors as well as minimal residence time. Therefore, the formulation of AMPs is essential to enhance stability, prolong delivery, and optimize effectiveness at the wound site. Different topical formulations of AMPs have been developed so far including nanoparticles, hydrogels, creams, ointments, and wafers to aid in controlling bacterial infection and enhance wound healing process in vivo. Herein, an overview is provided of the AMPs and current understanding of their formulations for topical wound healing applications along with suitable examples. Furthermore, future prospects for the development of effective combination AMP formulations are discussed. STATEMENT OF SIGNIFICANCE: Chronic wound infection and subsequent development of antibiotic resistance are serious clinical problems affecting millions of people worldwide. Antimicrobial peptides (AMPs) possess great potential in effectively killing the bacteria with minimal risk of resistance development. However, AMPs susceptibility to degradation following topical application limits their antimicrobial and wound healing effects. Therefore, development of an optimized topical formulation with high peptide stability and sustained AMP delivery is necessary to maximize the antimicrobial and wound healing effects. The present review provides an overview of the state-of-art in the field of topical AMP formulations for wound healing. Current developments in the field of topical AMP formulations are reviewed and future prospects for the development of effective combination AMP formulations are discussed.

Little Antimicrobial Peptides with Big Therapeutic Roles

Antimicrobial Peptides (AMPs) are short amphipathic biological molecules generally with less than 100 amino acids. AMPs not only present high bioactivities against bacteria, fungi or protists-induced infections, but also play important roles in anticancer activity, immune response and inflammation regulation. AMPs are classified as ribosomally synthesized, non-ribosomally synthesized and post-translationally modified, non-ribosomally synthesized ones and several synthetic or semisynthetic peptides according to their synthesis with or without the involvement of ribosomes. The molecular characterization and bioactivity action mechanisms are summarized for several ribosomally synthesized AMPs and main non-ribosomally synthesized members (cyclopeptides, lipopeptides, glycopeptides, lipoglycopeptides). We also analyze challenges and new strategies to overcome drug resistance and application limitations for AMP discovery. In conclusion, the growing novel small molecular AMPs have huge therapeutic potentials of antibacterial, antiviral, anticancer and immunoregulatory bioactivities through new techniquesdriven drug discovery strategy including bioinformatics prediction, de novo rational design and biosynthesis.

From biomedicinal to in silico models and back to therapeutics: a review on the advancement of peptidic modeling

Bioactive peptides participate in numerous metabolic functions of living organisms and have emerged as potential therapeutics on a diverse range of diseases. Albeit peptide design does not go without challenges, overwhelming advancements on in silico methodologies have increased the scope of peptide-based drug design and discovery to an unprecedented amount. Within an in silico model versus an experimental validation scenario, this review aims to summarize and discuss how different in silico techniques contribute at present to the design of peptide-based molecules. Published in silico results from 2014 to 2018 were selected and discriminated in major methodological groups, allowing a transversal analysis, promoting a landscape vision and asserting its increasing value in drug design.

Green synthesis of silver nanoparticles: biomolecule-nanoparticle organizations targeting antimicrobial activity

Since discovery of the first antibiotic drug, penicillin, in 1928, a variety of antibiotic and antimicrobial agents have been developed and used for both human therapy and industrial applications. However, excess and uncontrolled use of antibiotic agents has caused a significant growth in the number of drug resistant pathogens. Novel therapeutic approaches replacing the inefficient antibiotics are in high demand to overcome increasing microbial multidrug resistance. In the recent years, ongoing research has focused on development of nano-scale objects as efficient antimicrobial therapies. Among the various nanoparticles, silver nanoparticles have gained much attention due to their unique antimicrobial properties. However, concerns about the synthesis of these materials such as use of precursor chemicals and toxic solvents, and generation of toxic byproducts have led to a new alternative approach, green synthesis. This eco-friendly technique incorporates use of biological agents, plants or microbial agents as reducing and capping agents. Silver nanoparticles synthesized by green chemistry offer a novel and potential alternative to chemically synthesized nanoparticles. In this review, we discuss the recent advances in green synthesis of silver nanoparticles, their application as antimicrobial agents and mechanism of antimicrobial mode of action.

A Review on Quantum Dots: Synthesis to In- silico Analysis as Next Generation Antibacterial Agents

Succumbing to Multi-Drug Resistant (MDR) bacteria is a great distress to the recent health care system. Out of the several attempts that have been made to kill MDR pathogens, a few gained short-lived success. The failures, of the discovered or innovated antimicrobials, were mostly due to their high level of toxicity to hosts and the phenomenal rate of developing resistance by the pathogens against the new arsenal. Recently, a few quantum dots were tested against the pathogenic bacteria and therefore, justified for potential stockpiling of next-generation antibacterial agents. The key players for antimicrobial properties of quantum dots are considered to be Reactive Oxygen Species (ROS). The mechanism of reaction between bacteria and quantum dots needs to be better understood. They are generally targeted towards the cell wall and membrane components as lipoteichoic acid and phosphatidyl glycerol of bacteria have been documented here. In this paper, we have attempted to simulate ZnS quantum dots and have analysed their mechanism of reaction as well as binding potential to the above bacterial membrane components using CDOCKER. Results have shown a high level of antibacterial activity towards several pathogenic bacteria which specify their potentiality for future generation antibacterial drug development.

Self-Assembled Antimicrobial Nanomaterials

Nanotechnology came to stay improving the quality of human life by reducing environmental contamination of earth and water with pathogens. This review discusses how self-assembled antimicrobial nanomaterials can contribute to maintain humans, their water and their environment inside safe boundaries to human life even though some of these nanomaterials display an overt toxicity. At the core of their strategic use, the self-assembled antimicrobial nanomaterials exhibit optimal and biomimetic organization leading to activity at low doses of their toxic components. Antimicrobial bilayer fragments, bilayer-covered or multilayered nanoparticles, functionalized inorganic or organic polymeric materials, coatings and hydrogels disclose their potential for environmental and public health applications in this review.

Synthesis, construction, and evaluation of self-assembled nano-bacitracin A as an efficient antibacterial agent in vitro and in vivo

Bacitracin A (BA) is an excellent polypeptide antibiotic that is active against gram-positive bacteria without triggering multidrug resistance. However, BA is inactive against gram-negative bacteria because of its inability to cross the outer membrane of these cells, and it has strong nephrotoxicity, thus limiting its clinical applications. Nanoantibiotics can effectively localize antibiotics to the periplasmic space of bacteria while decreasing the adverse effects of antibiotics. In this study, biodegradable hydrophobic copolymers of poly (d,l-lactide-co-glycolide) (PLGA) were attached to the N-termini of BA to design a novel class of self-assembled nano-bacitracin A (nano-BAs), and their potential as antibacterial agents was evaluated in vitro and in vivo. Nano-BAs had a core-shell structure with a mean diameter <150 nm. Impressively, nano-BAs had strong antibacterial properties against both gram-positive and gram-negative bacteria, and the distribution of antibacterial activity as a function of PLGA block length was skewed toward longer PLGA chains. No cytotoxicity against HK-2 cells or human red blood cells (hRBCs) was observed in vitro, suggesting good biocompatibility. A high local density of BA mass on the surface promoted endocytotic cellular uptake, and hydrophobic interactions between the PLGA block and lipopolysaccharide (LPS) facilitated the uptake of nano-BAs, thereby leading to greater antibacterial activities. In addition, Nano-BA_5K was found to be effective in vivo, and it served as an anti-infective agent for wound healing. Collectively, this study provides a cost-effective means of developing self-assembling nano-polypeptide antibiotic candidates with a broader antibacterial spectrum and a lower toxicity than commercially available peptide antibiotics, owing to their modification with biodegradable copolymers.

Delivery systems for antimicrobial peptides

Due to rapidly increasing resistance development against conventional antibiotics, finding novel approaches for the treatment of infections has emerged as a key health issue. Antimicrobial peptides (AMPs) have attracted interest in this context, and there is by now a considerable literature on the identification such peptides, as well as on their optimization to reach potent antimicrobial and anti-inflammatory effects at simultaneously low toxicity against human cells. In comparison, delivery systems for antimicrobial peptides have attracted considerably less interest. However, such delivery systems are likely to play a key role in the development of potent and safe AMP-based therapeutics, e.g., through reducing chemical or biological degradation of AMPs either in the formulation or after administration, by reducing adverse side-effects, by controlling AMP release rate, by promoting biofilm penetration, or through achieving co-localization with intracellular pathogens. Here, an overview is provided of the current understanding of delivery systems for antimicrobial peptides, with special focus on AMP-carrier interactions, as well as consequences of these interactions for antimicrobial and related biological effects of AMP-containing formulations.

Next-generation nanoantibacterial tools developed from peptides

Bacteria resistant against various antimicrobial compounds have emerged in many countries, and the age of resistance has just started. Among the more promising novel antimicrobial compounds on which current research is focusing are the antimicrobial peptides (AMPs). These are often less susceptible to bacterial resistance since multiple modifications in the cellular membranes, cell wall and metabolism are required to reduce their effectiveness. Most likely, the use of pure AMPs will be insufficient for controlling pathogenic bacteria, and innovative approaches are required to employ AMPs in new antibiotic treatments. Therefore, here we review novel bionanotechnological approaches, including nanofibers, nanoparticles and magnetic particles for effectively using AMPs in fighting infectious diseases.

Crede’s method in eye water finds a nanomedicine base: a potential candidate to control ophthalmia neonatorum

Lethal eye infections of newborns occur mostly due to their passage through the contaminated birth canal. In the pre-antibiotic era blindness from such infections was most challenging. This scenario changed after the 1880s with the use of Crede’s method (a drop of 2.0% silver nitrate solution into newborn’s eyes which was later reduced to 1.0%). This research is focused on finding the structure-function relationship between silver nitrate and tears which offer antimicrobial action. A reinvestigation of Crede’s method revealed a light-dependent instant formation of silver oxide nanoparticles (sizes 20–70 nm) with strong antimicrobial action against ocular pathogens. Nano-therapy would be the key reason behind the widely accepted use of silver nitrate eye drop as a prophylactic agent prior to the discovery of antibiotics. A scientific view on the age-old Crede’s method explores the use of nano-therapy as a prophylactic agent. When routine prophylaxis with topical antibiotics brings the risk of resistance, Crede’s method may, in the near future, offer a way to fight against ophthalmia neonatorum (ON) caused by antibiotic-resistant pathogens.

Antifungal nanofibers made by controlled release of sea animal derived peptide

Candida albicans is a common human-pathogenic fungal species with the ability to cause several diseases including surface infections. Despite the clear difficulties of Candida control, antimicrobial peptides (AMPs) have emerged as an alternative strategy for fungal control. In this report, different concentrations of antifungal Cm-p1 (Cencritchis muricatus peptide 1) were electrospun into nanofibers for drug delivery. The nanofibers were characterized by mass spectrometry confirming the presence of the peptide on the scaffold. Atomic force microscopy and scanning electronic microscopy were used to measure the diameters, showing that Cm-p1 affects fiber morphology as well as the diameter and scaffold thickness. The Cm-p1 release behavior from the nanofibers demonstrated peptide release from 30 min to three days, leading to effective yeast control in the first 24 hours. Moreover, the biocompatibility of the fibers were evaluated through a MTS assay as well as ROS production by using a HUVEC model, showing that the fibers do not affect cell viability and only nanofibers containing 10% Cm-p1-PVA improved ROS generation. In addition, the secretion of pro-inflammatory cytokines IL-6 and TNF-α by the HUVECs was also slightly modified by the 10% Cm-p1-PVA nanofibers. In conclusion, the electrospinning technique applied here allowed for the manufacture of biodegradable biomimetic nanofibrous extracellular membranes with the ability to control fungal infection.

Fermentation and Cost-Effective 13C/15N Labeling of the Nonribosomal Peptide Gramicidin S for Nuclear Magnetic Resonance Structure Analysis

Gramicidin S (GS) is a nonribosomally synthesized decapeptide from Aneurinibacillus migulanus. Its pronounced antibiotic activity is attributed to amphiphilic structure and enables GS interaction with bacterial membranes. Despite its medical use for over 70 years, the peptide-lipid interactions of GS and its molecular mechanism of action are still not fully understood. Therefore, a comprehensive structural analysis of isotope-labeled GS needs to be performed in its biologically relevant membrane-bound state, using advanced solid-state nuclear magnetic resonance (NMR) spectroscopy. Here, we describe an efficient method for producing the uniformly (13)C/(15)N-labeled peptide in a minimal medium supplemented by selected amino acids. As GS is an intracellular product of A. migulanus, we characterized the producer strain DSM 5759 (rough-convex phenotype) and examined its biosynthetic activity in terms of absolute and biomass-dependent peptide accumulation. We found that the addition of either arginine or ornithine increases the yield only at very high supplementing concentrations (1% and 0.4%, respectively) of these expensive (13)C/(15)N-labeled amino acids. The most cost-effective production of (13)C/(15)N-GS, giving up to 90 mg per gram of dry cell weight, was achieved in a minimal medium containing 1% (13)C-glycerol and 0.5% (15)N-ammonium sulfate, supplemented with only 0.025% of (13)C/(15)N-phenylalanine. The 100% efficiency of labeling is corroborated by mass spectrometry and preliminary solid-state NMR structure analysis of the labeled peptide in the membrane-bound state.