Rapid eradication of vancomycin and methicillin-resistant Staphylococcus aureus by MDP1 antimicrobial peptide coated on photocrosslinkable chitosan hydrogel: in vitro antibacterial and in silico molecular docking studies

Introduction

Antibiotic resistance and weak bioavailability of antibiotics in the skin due to systemic administration leads to failure in eradication of vancomycin- and methicillin-resistant Staphylococcus aureus (VRSA and MRSA)-associated wound infections and subsequent septicemia and even death. Accordingly, this study aimed at designing a photocrosslinkable methacrylated chitosan (MECs) hydrogel coated by melittin-derived peptide 1 (MDP1) that integrated the antibacterial activity with the promising skin regenerative capacity of the hydrogel to eradicate bacteria by burst release strategy.

Methods

The MECs was coated with MDP1 (MECs-MDP1), characterized, and the hydrogel-peptide interaction was evaluated by molecular docking. Antibacterial activities of MECs-MDP1 were evaluated against VRSA and MRSA bacteria and compared to MECs-vancomycin (MECs-vanco). Antibiofilm activity of MECs-MDP1 was studied by our novel 'in situ biofilm inhibition zone (IBIZ)' assay, and SEM. Biocompatibility with human dermal fibroblast cells (HDFs) was also evaluated.

Results and Discussion

Molecular docking showed hydrogen bonds as the most interactions between MDP1 and MECs at a reasonable affinity. MECs-MDP1 eradicated the bacteria rapidly by burst release strategy whereas MECs-vanco failed to eradicate them at the same time intervals. Antibiofilm activity of MECs-MDP1 were also proved successfully. As a novel report, molecular docking analysis has demonstrated that MDP1 covers the structure of MECs and also binds to lysozyme with a reasonable affinity, which may explain the inhibition of lysozyme. MECs-MDP1 was also biocompatible with human dermal fibroblast skin cells, which indicates its safe future application. The antibacterial properties of a photocrosslinkable methacrylated chitosan-based hydrogel coated with MDP1 antimicrobial peptide were successfully proved against the most challenging antibiotic-resistant bacteria causing nosocomial wound infections; VRSA and MRSA. Molecular docking analysis revealed that MDP1 interacts with MECs mainly through hydrogen bonds with reasonable binding affinity. MECs-MDP1 hydrogels eradicated the planktonic state of bacteria by burst release of MDP1 in just a few hours whereas MECs-vanco failed to eradicate them. inhibition zone assay showed the anti-biofilm activity of the MECs-MDP1 hydrogel too. These findings emphasize that MECs-MDP1 hydrogel would be suggested as a biocompatible wound-dressing candidate with considerable and rapid antibacterial activities to prevent/eradicate VRSA/MRSA bacterial wound infections.

Antifungal properties of cathelicidin LL-37: current knowledge and future research directions

The threat of fungal diseases is substantially underestimated worldwide, but they have serious consequences for humans, animals, and plants. Given the limited number of existing antifungal drugs together with the emergence of drug-resistant strains, many researchers have actively sought alternatives or adjuvants to antimycotics. The best way to tackle these issues is to unearth potential antifungal agents with new modes of action. Antimicrobial peptides are being hailed as a promising source of novel antimicrobials since they exhibit rapid and broad-spectrum microbicidal activities with a reduced likelihood of developing drug resistance. Recent years have witnessed an explosion in knowledge on microbicidal activity of LL-37, the sole human cathelicidin. Herein, we provide a summary of the current understanding about antifungal properties of LL-37, with particular emphasis on its molecular mechanisms. We further illustrate fruitful areas for future research. LL-37 is able to inhibit the growth of clinically and agronomically relevant fungi including Aspergillus, Candida, Colletotrichum, Fusarium, Malassezia, Pythium, and Trichophyton. Destruction of the cell wall integrity, membrane permeabilization, induction of oxidative stress, disruption of endoplasmic reticulum homeostasis, formation of autophagy-like structures, alterations in expression of numerous fungal genes, and inhibition of cell cycle progression are the key mechanisms underlying antifungal effects of LL-37. Burgeoning evidence also suggests that LL-37 may act as a potential anti-virulence peptide. It is hoped that this review will not only motivate researchers to conduct more detailed studies in this field, but also inspire further innovations in the design of LL-37-based drugs for the treatment of fungal infections.

Antibacterial Efficacy of a Chitosan-Based Hydrogel Modified With Epsilon-Poly-l-Lysine Against Pseudomonas aeruginosa in a Murine-Infected Burn Wound Model

INTRODUCTION

Because antibiotic resistance is increasing worldwide and the leading cause of death in burn patients is an infection, an urgent need exists for nonantibiotic approaches to eliminate multidrug-resistant bacteria from burns to prevent their systemic dissemination and sepsis. We previously demonstrated the significant antibiofilm activity of a chitosan (CS) hydrogel containing the antimicrobial peptide epsilon-poly-l-lysine (EPL) against multidrug-resistant Pseudomonas aeruginosa using ex vivo porcine skin. In this study, we evaluated the in vivo antibacterial efficacy of a CS/EPL hydrogel against P. aeruginosa in a murine burn wound infection model.

MATERIALS AND METHODS

Full-thickness burns were created on the dorsum using a heated brass rod and were inoculated with bioluminescent, biofilm-forming P. aeruginosa (Xen41). Mice were treated with CS/EPL, CS, or no hydrogel applied topically 2 or 24 hours after inoculation to assess the ability to prevent or eradicate existing biofilms, respectively. Dressing changes occurred daily for 3 days, and in vivo bioluminescence imaging was performed to detect and quantitate bacterial growth. Blood samples were cultured to determine systemic infection. In vitro antibacterial activity and cytotoxicity against human primary dermal fibroblasts, keratinocytes, and mesenchymal stem cells were also assessed.

RESULTS

CS/EPL treatment initiated at early or delayed time points showed a significant reduction in bioluminescence imaging signal compared to CS on days 2 and 3 of treatment. Mice administered CS/EPL had fewer bloodstream infections, lower weight loss, and greater activity than the untreated and CS groups. CS/EPL reduced bacterial burden by two orders of magnitude in vitro and exhibited low cytotoxicity against human cells.

CONCLUSION

A topical hydrogel delivering the antimicrobial peptide EPL demonstrates in vivo efficacy to reduce but not eradicate established P. aeruginosa biofilms in infected burn wounds. This biocompatible hydrogel shows promise as an antimicrobial barrier dressing for the sustained protection of burn wounds from external bacterial contamination.

Fast killing kinetics, significant therapeutic index, and high stability of melittin-derived antimicrobial peptide

The emergence of multidrug-resistant (MDR) bacteria is a major challenge for antimicrobial chemotherapy. Concerning this issue, antimicrobial peptides (AMPs) have been presented as novel promising antibiotics. Our previous de novo designed melittin-derived peptides (MDP1 and MDP2) indicated their potential as peptide drug leads. Accordingly, this study was aimed to evaluate the kinetics of activity, toxicity, and stability of MDP1 and MDP2 as well as determination of their structures. The killing kinetics of MDP1 and MDP2 demonstrate that all bacterial strains were rapidly killed. MDP1 and MDP2 were ca. 100- and 26.6-fold less hemolytic than melittin and found to be respectively 72.9- and 41.6-fold less cytotoxic than melittin on the HEK293 cell line. MDP1 and MDP2 showed 252- and 132-fold improvement in their therapeutic index in comparison to melittin. MDP1 and MDP2 sustained their activities in the presence of human plasma and were found to be ca. four to eightfold more stable than melittin. Spectropolarimetry analysis of MDP1 and MDP2 indicates that the peptides adopt an alpha-helical structure predominantly. According to the fast killing kinetics, significant therapeutic index, and high stability of MDP1, it could be considered as a drug lead in a mouse model of septicemia infections.

Highly Synergistic Effects of Melittin With Vancomycin and Rifampin Against Vancomycin and Rifampin Resistant Staphylococcus epidermidis

Methicillin-resistant Staphylococcus epidermidis (MRSE) strains are increasingly emerging as serious pathogens because they can be resistant to many antibiotics called multidrug resistance (MDR) that limit the therapeutic options. In the case of vancomycin- and rifampin-resistant MDR-MRSE, the physicians are not allowed to increase the doses of antibiotics because of severe toxicity. Accordingly, we investigated the synergistic activity of melittin antimicrobial peptide with vancomycin and rifampin against vancomycin-resistant, and rifampin-resistant MDR-MRSE isolates. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), fractional inhibitory concentration index (FICi), and fractional bactericidal concentration index (FBCi) of antimicrobial agents against isolates were determined. Coagulate activities and serum and salt stability as well as melittin cytotoxicity on the human embryonic kidney (HEK) 293 cells and human red blood cells (RBCs) at their synergistic concentrations. MIC and MBC values for melittin were in the range of 0.312–2.5 and 0.312–5, respectively. Results also showed that the interaction of melittin with drugs was highly synergistic in which the geometric means of FICi and FBCi were < 0.5. Induced synergism led to a decrease in melittin, rifampin, and vancomycin concentrations by 8–1,020, 2–16, and 4–16-folds, respectively. This phenomenon caused a reduction in melittin toxicity by which the synergistic concentration of melittin needed to kill bacteria did not show cytotoxicity and hemolytic activity. Besides, no coagulation activity was found for the synergistic and alone concentrations of melittin in both Prothrombin Time (PT) and Partial Thromboplastin Time (PTT). Interestingly, the antibacterial activity of melittin in Mueller Hinton Broth (MHB) containing human serum did no significant differences between MIC and MBC values of melittin in MHB and MHB containing 10% human serum. The present findings showed that the therapeutic index of melittin was improved by 32.08- and 12.82-folds when combined with vancomycin and rifampin, respectively. Taken together, the obtained data show that melittin alone was effective against MDR-MRSE isolates and this antimicrobial peptide showed highly synergistic effects with vancomycin and rifampin without causing toxicity. Therefore, the combination of melittin and traditional antibiotics could be a promising strategy for the treatment of infections caused by MDR-MRSE.

Improving bactericidal performance of implant composite coatings by synergism between Melittin and tetracycline

Methicillin resistance Staphylococcus aureus bacteria (MRSA) are serious hazards of bone implants. The present study was aimed to use the potential synergistic effects of Melittin and tetracycline to prevent MRSA associated bone implant infection. Chitosan/bioactive glass nanoparticles/tetracycline composite coatings were deposited on hydrothermally etched titanium substrate. Melittin was then coated on composite coatings by drop casting method. The surfaces were analyzed by FTIR, XRD, and SEM instruments. Tetracycline in coatings revealed multifunctional behaviors include bone regeneration and antibacterial activity. Releasing ALP enzyme from MC3T3 cells increased by tetracycline, so it is suitable candidate as osteoinductive and antibacterial agent in orthopedic implants coatings. Melittin increased the proliferation of MC3T3 cells. Composite coatings with combination of tetracycline and Melittin eradicate all MRSA bacteria, while coatings with one of them could no t eradicate all of the bacteria. In conclusion, chitosan/bioactive glass/tetracycline/Melittin coating can be suggested as a multifunctional bone implant coating because of its osteogenic and promising antibacterial activity. Graphical abstract.

Prevention, inhibition, and degradation effects of melittin alone and in combination with vancomycin and rifampin against strong biofilm producer strains of methicillin-resistant Staphylococcus epidermidis

Methicillin-resistant Staphylococcus epidermidis (MRSE) bacteria are being recognized as true pathogens as they are able to resist methicillin and commonly form biofilms. Recent studies have shown that antimicrobial peptides (AMPs) are promising agents against biofilm-associated bacterial infections. In this study, we aimed to explore the antibiofilm activity of melittin, either alone or in combination with vancomycin and rifampin, against biofilm-producing MRSE strains. Minimum biofilm preventive concentration (MBPC), minimum biofilm inhibition concentration (MBIC), and minimum biofilm eradication concentration (MBEC), as well as fractional biofilm preventive-, inhibitory-, and eradication concentrations (FBPCi, FBICi, and FBECi), were determined for the antimicrobial agents tested. Cytotoxicity and hemolytic activity of melittin at its synergistic concentration were examined on human embryonic kidney cells (HEK-293) and Red Blood Cells (RBCs), respectively. The effect of melittin on the downregulation of biofilm-associated genes was explored using Real-Time PCR. MBPC, MBIC, and MBEC values for melittin were in the range of 0.625-20, 0.625-20, and 10-40 μg/μL, respectively. Melittin showed high synergy (FBPCi, FBICi and FBECi < 0.5). The synergism resulted in a 64-512-fold, 2-16 and 2-8-fold reduction in melittin, rifampicin and vancomycin concentrations, respectively. The synergistic melittin concentration found to be effective did not manifest either cytotoxicity on HEK-293 or hemolytic activity on RBCs. Results showed that melittin downregulated the expression of biofilm-associated icaA, aap, and psm genes in all isolates tested, ranging from 0.04-folds to 2.11-folds for icaA and from 0.05 to 3.76-folds for aap and psm. The preventive and therapeutic indexes of melittin were improved 8-fold when combined with vancomycin and rifampin. Based on these findings, the combination of melittin with conventional antibiotics could be proposed for treating or preventing biofilm-associated MRSE infections.

Antibacterial Potential of a Novel Peptide from the Consensus Sequence of Dermaseptin Related Peptides Secreted by Agalychnis annae

BACKGROUND

The consistently increasing reports of bacterial resistance and the reemergence of bacterial epidemics have inspired the health and scientific community to discover new molecules with antibacterial potential continuously. Frog-skin secretions constitute bioactive compounds essential for finding new biopharmaceuticals. The exact antibacterial characterization of dermaseptin related peptides derived from Agalychnis annae, is limited. The resemblance in their conserved and functionally linked genomes indicates an unprecedented opportunity to obtain novel bioactive compounds.

OBJECTIVE

In this study, we derived a novel peptide sequence and determined its antibacterial potentials.

METHODS

Consensus sequence strategy was used to design the novel and active antibacterial peptide named 'AGAAN' from skin secretions of Agalychnis annae. The in-vitro activities of the novel peptide against some bacterial strains were investigated. Time kill studies, DNA retardation, cytotoxicity, betagalactosidase, and molecular computational studies were conducted.

RESULTS

AGAAN inhibited P. aeruginosa, E. faecalis, and S. typhimurium at 20 μM concentration. E. coli and S. aureus were inhibited at 25 μM, and lastly, B. subtilis at 50 μM. Kinetics of inactivation against exponential and stationary growing bacteria was found to be rapid within 1-5 hours of peptide exposure, depending on time and concentration. The peptide displayed weak hemolytic activity between 0.01%-7.31% at the antibacterial concentrations. AGAAN efficiently induced bacterial membrane damage with subsequent cell lysis. The peptide's DNA binding shows that it also targets intracellular DNA by retarding its movement. Our in-silico molecular docking analysis displayed a strong affinity to the bacterial cytoplasmic membrane.

CONCLUSION

AGAAN exhibits potential antibacterial properties that could be used to combat bacterial resistance.

Eradication of vancomycin-resistant Staphylococcus aureus on a mouse model of third-degree burn infection by melittin: An antimicrobial peptide from bee venom

Third-degree burn infections caused by antibiotic-resistant bacteria are of high clinical concern. Chemical antibiotics are not promising in eradication of bacterial infections. In this challenging condition, antimicrobial peptides (AMPs) are recently introduced as novel promising agents to overcome the issue. Accordingly, our study aimed to evaluate the efficiency of 'melittin' as natural peptide in bee venom, in eradicating vancomycin resistant Staphylococcus aureus (VRSA) on a mouse model of third-degree burn infection. In vitro pharmacological value of melittin was determined by examining its inhibitory and killing activities on VRSA isolates at different doses and time periods. The action mechanism of 'melittin' was evaluated by fluorescent release assay and Field Emission Scanning Electron Microscopy (FE-SEM) analyses. In vivo activity and toxicity of melittin were also examined on a mouse model of third-degree burn infection. The Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration (MBC) of melittin on all isolates ranged from '0.125-2 μg/mL' and '0.125-4 μg/mL', respectively. Rapid antibacterial activity of melittin on VRSA isolates was demonstrated by killing kinetics assays. Fluorometric and FE-SEM analyses indicated the membranolytic effects of melittin on VRSA isolates. The colonized VRSA bacteria were eradicated by melittin at 16 μg, in a single dose. No dermal toxicity and in vivo hemolysis were observed in the examined mice. The lack of in vivo toxicity of melittin along with its potent antibacterial activity indicated its promising therapeutic value as a topical drug against S. aureus associated third-degree burn infections.

Nisin loaded carbopol gel against Pseudomonas aeruginosa infected third-degree burns: A therapeutic intervention

The emergence of multidrug resistant strains of Pseudomonas aeruginosa necessitates the exploration of novel therapeutic intervention (s). The present study aimed to develop a nisin loaded carbopol gel formulation (NLCG) and explore its therapeutic efficacy against P. aeruginosa infected burn wounds. The formulation was prepared using Carbopol 940 as a polymer and characterized in terms of its appearance, stability, pH, rheology, spreadability, release, and permeation profiles. Disc diffusion assay and field emission scanning electron microscopy were carried out to establish in vitro antibacterial activity while the in vitro cytotoxicity was evaluated by hemolytic and trypan blue exclusion assay. Furthermore, in vivo efficacy was investigated by developing P. aeruginosa infected third-degree murine burn wound model followed by evaluation of parameters like bacterial loads, skin restoration, histopathological architecture, levels of hydroxyproline, myeloperoxidase and cytokines. Our studies yielded a stable formulation with pH, viscosity and drug release flux values as 6.5 ± 0.02, 382.4 p and 160.55 ± 3.64 μg h^-1  cm^-2 , respectively. Approximately, 84.02 ± 1.63% of nisin was found to permeate into murine skin, further, affirmed by confocal microscopic observations. Interestingly, no in vitro cytotoxicity of NLCG (to erythrocytes and/or to peritoneal macrophages) could be observed. The log units decrease (s) in CFUs of Pseudomonas in skin were found to be 1.5137, 4.2257, 6.456 after 12, 24 and 72 h of topical gel therapy, respectively. Percentage wound closure, tensile strength, histological, and scanning electron microscopic studies further provided a healing evidence with skin showing restoration of the epithelium. The gel therapy also led to a significant modulation (p ≤ 0.05) in hydroxyproline content, myeloperoxidase levels, and serum levels of IL-1, IL-10, and TNF-α. Our formulation revealed anti-Pseudomonas, wound healing, and immunomodulatory efficacy of NLCG. Further investigations are warranted to determine the underlying mechanism (s) of these displayed antibacterial and immunomodulatory effects.

Anti-Staphylococcal and cytotoxic activities of the short anti-microbial peptide PVP

Over the past years, short anti-microbial peptides have drawn growing attention in the research and trade literature because they are usually capable of killing a broad spectrum of pathogens by employing unique mechanisms of action. This study aimed to evaluate the anti-bacterial effects of a previously designed peptide named PVP towards the clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) in vitro. Secondary structure, cytotoxicity, and membrane-permeabilizing effects of the peptide were also assessed. PVP had a tendency to adopt alpha-helical conformation based upon structural predictions and circular dichroism spectroscopy (in 50% trifluoroethanol). The peptide showed MIC values ranging from 1 to 16 µg/mL against 10 strains of MRSA. In contrast to ciprofloxacin and gentamicin, PVP at sub-lethal concentration (1 µg/mL) did not provoke the development of peptide resistance after 14 serial passages. Remarkably, 1 h of exposure to 4 × MBC of PVP (8 µg/mL) was sufficient for total bacterial clearance, whereas 4 × MBC of vancomycin (8 µg/mL) failed to totally eradicate bacterial cells, even after 8 h. PVP showed negligible cytotoxicity against human dermal fibroblasts at concentrations required to kill the MRSA strains. The results of flow cytometric analysis and fluorescence microscopy revealed that PVP caused bacterial membrane permeabilization, eventually culminating in cell death. Owing to the potent anti-bacterial activity, fast bactericidal kinetics, and negligible cytotoxicity, PVP has the potential to be used as a candidate antibiotic for the topical treatment of MRSA infections.

Near-Infrared Fluorescent Peptides with High Tumor Selectivity: Novel Probes for Image-Guided Surgical Resection of Orthotopic Glioma

The complete excision of glioblastomas with maximal retention of surrounding normal tissues can have a positive effect on the survival status and quality of life of patients. Near-infrared fluorescence (NIRF) optical imaging of the tumor vasculature offers a noninvasive method for detection of early stage glioblastoma and efficient monitoring of therapeutic responses. The aim of this study was to develop a novel NIRF imaging probe as a visualization tool for image-guided surgical resection of orthotopic glioblastoma. In this study, Cy5.5-RKL, Cy5.5-NKL, and Cy5.5-DKL probes were successfully synthesized, and their properties were investigated in vitro and in vivo. In vivo, Cy5.5-RKL and Cy5.5-NKL were able to detect U87MG xenografts for at least 8 h post injection. The maximum tumor-to-muscle ratios of Cy5.5-RKL and Cy5.5-NKL were 7.65 ± 0.72 and 5.43 ± 0.72, respectively. Of the probes, Cy5.5-RKL displayed the best delineation of the boundaries between orthotopic glioblastomas and normal brain tissue at 8 h p.i. In conclusion, NIRF imaging using Cy5.5-RKL is promising not only for diagnostic purposes but also for use in image-guided surgery for orthotopic glioblastoma or other superficial tumors.

The activity and action mechanism of novel short selective LL-37-derived anticancer peptides against clinical isolates of Escherichia coli

Human cathelicidin LL-37 has recently attracted interest as a potential therapeutic agent, mostly because of its ability to kill a wide variety of pathogens and cancer cells. In this study, we aimed to investigate the antibacterial activity and cytotoxicity of previously designed LL-37 anticancer derivatives (i.e., P7, P22, and P38). Calcein release assay and field emission-scanning electron microscopy (FE-SEM) were performed to elucidate the possible mechanism of action of P38, the peptide with the highest bactericidal activity. In silico analysis demonstrated the amphipathic alpha-helical structure for three peptides. Antibacterial activity of P38 against multidrug-resistant (MDR) clinical isolates of Escherichia coli was higher than that of P7 and P22. P38 caused no hemolysis or cytotoxicity. Treating calcein-loaded E. coli with 4× MIC of P38 resulted in more than 96% leakage of calcein. Noticeably, FE-SEM revealed that P38 killed E. coli by disrupting the bacterial membrane. Molecular docking studies showed that P38 had a much higher affinity for the outer membrane of Gram-negative bacteria compared with both P22 and P7. Owing to the bactericidal activity of P38 against MDR E. coli isolates and its negligible cytotoxicity, P38 has the potential for further studies in a mouse model of infectious disease.