Conformationally tuned antibacterial oligomers target the peptidoglycan of Gram-positive bacteria

Near-infrared light triggered upconversion nanocomposites with multifunction of enhanced antimicrobial photodynamic therapy and gas therapy for inflammation regulation

Antibacterial photodynamic therapy (aPDT) is highly effective in killing bacteria, while the problem of hypoxia and limited light penetration in deep tissue has not been properly solved. In addition, few aPDT works take into account the regulation of inflammation, which is an important regulatory process after antimicrobial therapy and the final purpose of treatment. In this work, to address the above isssues, we have designed a multi-functional composite UCNPs-Ce6-Mn(CO)5Br@Silane (referred to as UCM@Si), which consists of several key components: Up-conversion nanoparticles (UCNPs: NaErF4:Tm3+@NaYF4:Yb3+), Chlorin e6 (Ce6) and Manganese pentacarbonyl bromide (Mn(CO)5Br). When exposed to near-infrared (NIR) light (980 nm), the UCNPs can emit strong red light at 655 nm which further trigger the aPDT of Ce6. The generated reactive oxygen (ROS) subsequently break the metal carbonyl bond of Mn(CO)5Br, leading to the production of carbon monoxide (CO) molecules as well as manganese ions (Mn2+), which further decomposes hydrogen peroxide (H2O2) in the microenvironment to oxygen (O2). Therefore, this simple nanocomposite not only provides substantial self-oxygen replenishment for enhanced aPDT, but also facilitates effective inflammation regulation via CO across a wide range of deep infections. This approach leverages the unique properties of these materials to combat bacterial infections by simultaneously killing bacteria, regulating inflammation, and enhancing the oxygen levels in the affected microenvironment. This O2 and CO gas based aPDT treatment system offers a promising approach to comprehensively address microbial-induced infectious diseases, particularly deep infections, holding the potential clinical applications.

A Versatile Approach for the Synthesis of Antimicrobial Polymer Brushes on Natural Rubber/Graphene Oxide Composite Films via Surface-Initiated Atom-Transfer Radical Polymerization

A simple strategy was adopted for the preparation of an antimicrobial natural rubber/graphene oxide (NR/GO) composite film modified through the use of zwitterionic polymer brushes. An NR/GO composite film with antibacterial properties was prepared using a water-based solution-casting method. The composited GO was dispersed uniformly in the NR matrix and compensated for mechanical loss in the process of modification. Based on the high bromination activity of α-H in the structure of cis-polyisoprene, the composite films were brominated on the surface through the use of N-bromosuccinimide (NBS) under the irradiation of a 40 W tungsten lamp. Polymerization was carried out on the brominated films using sulfobetaine methacrylate (SBMA) as a monomer via surface-initiated atom transfer radical polymerization (SI-ATRP). The NR/GO composite films modified using polymer brushes (PSBMAs) exhibited 99.99% antimicrobial activity for resistance to Escherichia coli and Staphylococcus aureus. A novel polymer modification strategy for NR composite materials was established effectively, and the enhanced antimicrobial properties expand the application prospects in the medical field.

Chickpea-Derived Modified Antimicrobial Peptides KTA and KTR Inactivate Staphylococcus aureus via Disrupting Cell Membrane and Interfering with Peptidoglycan Synthesis

The widespread bacterial contamination caused by foodborne pathogens has continuously driven the development of advanced and potent food antimicrobial agents. In this study, two novel antimicrobial peptides (AMPs) named KTA and KTR were obtained by modifying a natural AMP, Leg2, from chickpea storage protein legumin hydrolysates. They were further predicted to be stable hydrophobic cationic AMPs of α-helical structure with no hemolytic toxicity by several online servers. Moreover, the AMPs exerted superior antibacterial activity against two representative Staphylococcus aureus strains thanks to the increased hydrophobicity and positive charge, with minimum inhibition concentration value (4.74-7.41 μM) significantly lower than that of Leg2 (>1158.70 μM). Further, this study sought to elucidate the specific antimicrobial mechanism against Gram-positive bacteria. It was found that the electrostatic interactions of the AMPs with peptidoglycan were vital for peptide activity in combating Gram-positive bacteria. Subsequently, the cell membrane of S. aureus cells was irreversibly disrupted by increasing permeability and impairing membrane components, which led to the massive release of intracellular substances and eventual cell death. Overall, this work demonstrated that KTA and KTR were active against Gram-positive bacteria via peptidoglycan targeting and membrane-disruptive mechanisms and paved the way for expanding their application potential to alleviate food contamination.

Biological Activities of Zinc Oxide Nanoparticles Green Synthesized Using the Aqueous Extract of Dracocephalum kotschyi Boiss

BACKGROUND

Dracocephalum kotschyi Boiss. is known as a native medicinal plant of Iran.

OBJECTIVE

In this study, aqueous extract of D. kotschyi was used to synthesize ZnO-NPs. To produce ZnO-NPs, aerial parts of D. kotschyi were powdered and then macerated for obtaining aqueous extract, after that, aqueous extract was used to reduse zinc nitrate to ZnO-NPs.

METHODS

To confirm nanoparticles synthesis, SEM, TEM, UV-Vis, FTIR, and XRD were used. The synthesized ZnO-NPs were studied for antimicrobial activities by microdilution method for calculating MIC and MBC. Analysis of ZnO-NPs confirmed successful synthesis by extract of D. kotschyi.

RESULTS

The sizes of ZnO-NPs were estimated 50-200 nm in diameter. Antibacterial and antifungal experiments showed potent activities against Staphylococos aureus, Pseudomonas aeruginosa and Candida albicans. The results of the studies showed that the nanoparticles synthesized with the aqueous extract of D. kotschyi have a much greater antimicrobial effect than the aqueous extract of D. kotschyi and zinc nanoparticles, each alone (MIC values 3.7 to 7.5 mg/ml).

CONCLUSION

The noteworthy point is that the inhibitory rate of synthesized zinc oxide nanoparticles is higher compared to broad-spectrum antibiotics, such as chloramphenicol (MIC values 15 mg/ml). Determining the therapeutic and toxic dose of this product for humans requires further investigation and clinical trials.

Ultrasonically functionalized chitosan-gallic acid films inactivate Staphylococcus aureus through envelope-disruption under UVA light exposure

The significant threat of foodborne pathogens contamination has continuously promoted the development of efficient antimicrobial food packaging materials. Here, an antimicrobial film was prepared with gallic acid-grafted-chitosan (CS/GA) that obtained by a two-step ultrasound method. The resultant films exhibited good transparency, improved UV barrier performance, and enhanced mechanical strength. Specifically, with the grafting of 1.2 % GA, the UV blocking ability of CS/GA film at 400 nm was significantly increased by 19.7 % and the tensile strength was nearly two times higher than that of CS film. Moreover, the CS/GA films exhibited an inspiring photoactivated bactericidal ability under 400 nm UVA light irradiation that eradicated almost 99.9 % of Staphylococcus aureus (S. aureus) cells within 60 min. To gain more insights into the antibacterial mechanism, the treated S. aureus cells were further investigated by visualizing bacterial ultrastructure and analyzing membrane properties. The results pointed to the peptidoglycan layer as the primary action target when bacteria come into contact with CS/GA films. Afterward, the intracellular oxidative lesions, disrupted bacterial integrity, and disordered membrane functional properties collectively resulted in eventual cell death. The findings revealed the unique peptidoglycan targeting and membrane disruptive mechanisms of CS/GA films, confirming the application values in controlling foodborne pathogens.

Dual-network hydrogels based on dynamic imine and borate ester bonds with antibacterial and self-healing properties

Polymeric hydrogel materials with multiple functions are in great demand in practical biomedical scenarios. In this work, a self-healing hydrogel with both antimicrobial properties was prepared using a strategy that combines dynamic imine and borate ester bonds. In this hydrogel, polyvinyl alcohol (PVA) is used as the base network, and borax solution as the cross-linking agent, and borate ester bonds can be formed between these two. Dialdehyde carboxymethyl cellulose (DCMC) was selected to cross-link with the amino groups in carboxymethyl chitosan (CMCS) and polyethyleneimine (PEI) to form dynamic imine bonds. The PVA/PEI/DCMC/CMCS hydrogels prepared by double chemical cross-linking have good mechanical properties (maximum tensile strength up to 289 KPa and strain at the break up to 1025%). Due to the uniqueness of the two chemical bonds, the hydrogel material is self-healing at room temperature without additional stimulation. In addition, the inherent antibacterial properties of the raw materials in this hydrogel confer antibacterial properties, with a kill rate of up to 99% against E. coli and S. aureus. The multifunctional hydrogels developed in this study provide more ideas and references for the future application of hydrogel materials in practical scenarios.

A hybrid and scalable nanofabrication approach for bio-inspired bactericidal silicon nanospike surfaces

Insects and plants exhibit bactericidal properties through surface nanostructures, such as nanospikes, which physically kill bacteria without antibiotics or chemicals. This is a promising new avenue for achieving antibacterial surfaces. However, the existing methods for fabricating nanospikes are incapable of producing uniform nanostructures on a large scale and in a cost-effective manner. In this paper, a scalable nanofabrication method involving the application of nanosphere lithography and reactive ion etching for constructing nanospike surfaces is demonstrated. Low-cost silicon nanospikes with uniform spacing that were sized similarly to biological nanospikes on cicada wings with a 4-inch wafer scale were fabricated. The spacing, tip radius, and base diameter of the silicon nanospikes were controlled precisely by adjusting the nanosphere diameters, etching conditions, and diameter reduction. The bactericidal properties of the silicon nanospikes with 300 nm spacing were measured quantitatively using the standard viability plate count method; they killed E. coli cells with 59 % efficiency within 30 h. The antibacterial ability of the nanospike surface was further indicated by the morphological differences between bacteria observed in the scanning electron microscopic images as well as the live/dead stains of fluorescence signals. The fabrication process combined the advantages of both top-down and bottom-up methods and was a significant step toward affordable bio-inspired antibacterial surfaces.

An optimized antimicrobial peptide analog acts as an antibiotic adjuvant to reverse methicillin-resistant Staphylococcus aureus

The misuse of antibiotics in animal protein production has driven the emergence of a range of drug-resistant pathogens, which threaten existing public health security. Consequently, there is an urgent need to develop novel antimicrobials and new infection treatment options to address the challenges posed by the dramatic spread of antibiotic resistance. Piscidins, a class of fish-specific antimicrobial peptides (AMPs), are regarded as promising therapies for biomedical applications. Progress towards potential analogs from the piscidin family has been hampered by unenforceable structural optimization strategies. Here, we leverage a strategy of bioinformatics analysis combined with molecular dynamics (MD) simulation to identify specific functional hotspots in piscidins and rationally design related analogues. As expected, this approach yields a potent and non-toxic PIS-A-1 that can be used as an antibiotic adjuvant to reverse methicillin-resistant Staphylococcus aureus (MRSA) pathogens. Remarkably, the structural optimization scheme and application strategy proposed here will contribute richer therapeutic options for the safe production of animal protein.

Synthesis and Antibacterial Properties of Oligomeric Dehydrogenation Polymer from Lignin Precursors

The lignin precursors of coniferin and syringin were synthesised, and guaiacyl-type and guaiacyl-syringyl-type oligomeric lignin dehydrogenation polymers (DHP and DHP-GS) were prepared with the bulk method. The carbon-13 nuclear magnetic resonance spectroscopy showed that both DHP-G and DHP-GS contained β-O-4, β-5, β-β, β-1, and 5-5 substructures. Extraction with petroleum ether, ether, ethanol, and acetone resulted in four fractions for each of DHP-G (C11-C14) and DHP-GS (C21-C24). The antibacterial experiments showed that the fractions with lower molecular weight had relatively strong antibacterial activity. The ether-soluble fractions (C12 of DHP-G and C22 of DHP-GS) had strong antibacterial activities against E. coli and S. aureus. The C12 and C22 fractions were further separated by preparative chromatography, and 10 bioactive compounds (G1-G5 and GS1-GS5) were obtained. The overall antibacterial activities of these 10 compounds was stronger against E. coli than S. aureus. Compounds G1, G2, G3, and GS1, which had the most significant antibacterial activities, contained β-5 substructures. Of these, G1 had the best antibacterial activity. Its inhibition zone diameter was 19.81 ± 0.82 mm, and the minimum inhibition concentration was 56.3 ± 6.20 μg/mL. Atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) showed that the antibacterial activity of G1 was attributable to a phenylcoumarin dimer, while the introduction of syringyl units reduced antibacterial activity.

Phytochemical content and potential health applications of pecan [Carya illinoinensis (Wangenh) K. Koch] nutshell

BACKGROUND

The pecan nutshell contains phytochemicals with various biological activities that are potentially useful in the prevention or treatment of diseases such as cancer, diabetes, and metabolic imbalances associated with heart diseases.

OBJECTIVE

To update this topic by means of a literature review and include those that contribute to the knowledge of the chemical composition and biological activities of pecan nutshell, particularly of those related to the therapeutic potential against some chronic degenerative diseases associated with oxidative stress.

METHOD

Exhaustive and detailed review of the existing literature using electronic databases.

CONCLUSION

The pecan nutshell is a promising natural product with pharmaceutical uses in various diseases. However, additional research related to the assessment of efficient extraction methods and characterization, particularly the evaluation of the mechanisms of action in new in vivo models, is necessary to confirm these findings and development of new drugs with therapeutic use.

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Liquid metal polymer composite: Flexible, conductive, biocompatible, and antimicrobial scaffold

Gallium and its alloys, such as eutectic gallium indium alloy (EGaIn), a form of liquid metal, have recently attracted the attention of researchers due to their low toxicity and electrical and thermal conductivity for biomedical application. However, further research is required to harness EGaIn-composites advantages and address their application as a biomedical scaffold. In this research, EGaIn-polylactic acid/polycaprolactone composites with and without a second conductive filler, MXene, were prepared and characterized. The addition of MXene, into the EGaIn-composite, can improve the composite's electrochemical properties by connecting the liquid metal droplets resulting in electrically conductive continuous pathways within the polymeric matrix. The results showed that the composite with 50% EGaIn and 4% MXene, displayed optimal electrochemical properties and enhanced mechanical and radiopacity properties. Furthermore, the composite showed good biocompatibility, examined through interactions with fibroblast cells, and antibacterial properties against methicillin-resistant Staphylococcus aureus. Therefore, the liquid metal (EGaIn) polymer composite with MXene provides a first proof-of-concept engineering scaffold strategy with low toxicity, functional electrochemical properties, and promising antimicrobial properties.

Surface-initiated atom-transfer radical polymerization (SI-ATRP) of bactericidal polymer brushes on poly(lactic acid) surfaces

We have modified the surface of poly(lactic acid) (PLA) by bromination in the presence of N-bromosuccinimide (NBS) under UV irradiation. This new approach to impart functionality to the surface does not effect the bulk of the material. Brominated PLA surfaces served as initiators for atom-transfer radical polymerization (SI-ATRP) of 2-(methacryloyloxy)ethyl]trimethylammonium chloride, a quaternary ammonium methacrylate (QMA). Grafting of poly(QMA) brushes rendered PLA films hydrophilic and these films displayed a three-order of magnitude increase in antimicrobial efficacy against Gram-negative bacteria such as Escherichia coli as compared to unmodified PLA. The two-step strategy described here to modify PLA surface represents a useful route to modified PLA materials for biomedical and antimicrobial packaging applications.

Systematic Comparison of the Structural and Dynamic Properties of Commonly Used Water Models for Molecular Dynamics Simulations

Water is a unique solvent that is ubiquitous in biology and present in a variety of solutions, mixtures, and materials settings. It therefore forms the basis for all molecular dynamics simulations of biological phenomena, as well as for many chemical, industrial, and materials investigations. Over the years, many water models have been developed, and it remains a challenge to find a single water model that accurately reproduces all experimental properties of water simultaneously. Here, we report a comprehensive comparison of structural and dynamic properties of 30 commonly used 3-point, 4-point, 5-point, and polarizable water models simulated using consistent settings and analysis methods. For the properties of density, coordination number, surface tension, dielectric constant, self-diffusion coefficient, and solvation free energy of methane, models published within the past two decades consistently show better agreement with experimental values compared to models published earlier, albeit with some notable exceptions. However, no single model reproduced all experimental values exactly, highlighting the need to carefully choose a water model for a particular study, depending on the phenomena of interest. Finally, machine learning algorithms quantified the relationship between the water model force field parameters and the resulting bulk properties, providing insight into the parameter-property relationship and illustrating the challenges of developing a water model that can accurately reproduce all properties of water simultaneously.

Emerging Antibacterial Strategies with Application of Targeting Drug Delivery System and Combined Treatment

At present, some bacteria have developed significant resistance to almost all available antibiotics. One of the reasons that cannot be ignored is long-term exposure of bacteria to the sub-minimum inhibitory concentration (MIC) of antibiotics. Therefore, it is necessary to develop a targeted antibiotic delivery system to improve drug delivery behavior, in order to delay the generation of bacterial drug resistance. In recent years, with the continuous development of nanotechnology, various types of nanocarriers that respond to the infection microenvironment, targeting specific bacterial targets, and targeting infected cells, and so on, are gradually being used in the delivery of antibacterial agents to increase the concentration of drugs at the site of infection and reduce the side effects of drugs in normal tissues. Here, this article describes in detail the latest research progress on nanocarriers for antimicrobial, and commonly used targeted antimicrobial strategies. The advantages of the combination of nanotechnology and targeting strategies in combating bacterial infections are highlighted in this review, and the upcoming opportunities and remaining challenges in this field are rationally prospected.

Antipathogenic properties and applications of low-dimensional materials

A major health concern of the 21st century is the rise of multi-drug resistant pathogenic microbial species. Recent technological advancements have led to considerable opportunities for low-dimensional materials (LDMs) as potential next-generation antimicrobials. LDMs have demonstrated antimicrobial behaviour towards a variety of pathogenic bacterial and fungal cells, due to their unique physicochemical properties. This review provides a critical assessment of current LDMs that have exhibited antimicrobial behaviour and their mechanism of action. Future design considerations and constraints in deploying LDMs for antimicrobial applications are discussed. It is envisioned that this review will guide future design parameters for LDM-based antimicrobial applications.

Fluorescent Magnesium Hydroxide Nanosheet Bandages with Tailored Properties for Biocompatible Antimicrobial Wound Dressings and pH Monitoring

Magnesium hydroxide (Mg(OH)₂) is hailed as a cheap and biocompatible material with antimicrobial potential; however, research aimed at instilling additional properties and functionality to this material is scarce. In this work, we synthesized novel, fluorescent magnesium hydroxide nanosheets (Mg(OH)₂-NS) with a morphology that closely resembles that of graphene oxide. These multifunctional nanosheets were employed as a potent antimicrobial agent against several medically relevant bacterial and fungal species, particularly on solid surfaces. Their strong fluorescence signature correlates to their hydroxide makeup and can therefore be used to assess their degradation and functional antimicrobial capacity. Furthermore, their pH-responsive change in fluorescence can potentially act as a pH probe for wound acidification, which is characteristic of healthy wound healing. These fluorescent antimicrobial nanosheets were stably integrated into biocompatible electrospun fibers and agarose gels to add functionality to the material. This reinforces the suitability of the material to be used as antimicrobial bandages and gels. The biocompatibility of the Mg(OH)₂-NS for topical medical applications was supported by its noncytotoxic action on human keratinocyte (HaCaT) cells.

Synthesis, characterization and antimicrobial activity applications of grafted copolymer alginate-g-poly(N-vinyl imidazole)

N-Vinyl imidazole was grafted onto sodium alginate (PNVI-g-NaAlg) through a free radical polymerization technique in aqueous solution using potassium persulfate (K2S2O8, KPS) initiator material. The conditions of the grafting process onto sodium alginate were adjusted to obtain a grafted copolymer with a high percentage of poly(N-vinyl imidazole). The prepared grafted copolymer sodium alginate (NaAlg-g-PNVI), with high percentage yield, was investigated and characterized under certain conditions in order to detect its antibacterial effect. The prepared grafted copolymer was considered by means of several systems such as Fourier-Transform Infrared spectroscopy (FT-IR), 1H NMR spectroscopy and thermal analysis. The change in the morphology of the alginate distinguished after the grafting process was confirmed using a Scanning Electron Microscope (SEM). The biological activity of the grafted material was considered using Escherichia coli, Neisseria gonorrhoeae (Gram-negative), Bacillus subtilis (Gram-positive) and Candida albicans antifungal activities through the agar diffusion method. The obtained results show excellent improvement in antimicrobial activity of the alginate by grafting against Bacillus subtilis, Escherichia coli, Neisseria gonorrhoeae, and Candida albicans.

Robust Copper Metal-Organic Framework-Embedded Polysiloxanes for Biomedical Applications: Its Antibacterial Effects on MRSA and In Vitro Cytotoxicity

Polysiloxanes (PSs) have been widely utilized in the industry as lubricants, varnishes, paints, release agents, adhesives, and insulators. In addition, their applications have been expanded to include the development of new biomedical materials. To modify PS for application in therapeutic purposes, a flexible antibacterial Cu-MOF (metal-organic framework) consisting of glutarate and 1,2-bis(4-pyridyl)ethane ligands was embedded in PS via a hydrosilylation reaction of vinyl-terminated and H-terminated PSs at 25 °C. The bactericidal activities of the resulting Cu-MOF-embedded PS (PS@Cu-MOF) and the control polymer (PS) were tested against Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus. PS@Cu-MOF exhibited more than 80% bactericidal activity toward the tested bacteria at a concentration of 100 μg⋅mL-1 and exhibited a negligible cytotoxicity toward mouse embryonic fibroblasts at the same concentration. Release tests of the Cu(II) ion showed PS@Cu-MOF to be particularly stable in a phosphate-buffered saline solution. Furthermore, its physical and thermal properties, including the phase transition, rheological measurements, swelling ratio, and thermogravimetric profile loss, were similar to those of the control polymer. Moreover, the low cytotoxicity and bactericidal activities of PS@Cu-MOF render it a promising candidate for use in medicinal applications, such as in implants, skin-disease treatment, wound healing, and drug delivery.

Polymeric approach to combat drug-resistant methicillin-resistant Staphylococcus aureus

ABSTRACT

The current global death rate has threatened humans due to increase in deadly unknown infections caused by pathogenic microorganisms. On the contrary, the emergence of multidrug-resistant bacteria is also increasing which is leading to elevated lethality rate worldwide. Development of drug-resistant bacteria has become one of the daunting global challenges due to failure in approaching to combat against them. Methicillin-resistant Staphylococcus aureus (MRSA) is one of those drug-resistant bacteria which has led to increase in global mortality rate causing various lethal infections. Polymer synthesis can be one of the significant approaches to combat MRSA by fabricating polymeric coatings to prevent the spread of infections. This review provides last decade information in the development of various polymers against MRSA.

GRAPHICAL ABSTRACT