Antimicrobial Nanostructures Research Articles

Superior Performance of Iron-Coated Silver Nanoparticles and Cefoxitin as an Antibiotic Composite Against Methicillin-Resistant Staphylococcus aureus (MRSA): A Population Study.

The synergistic effects of antimicrobial nanostructures with antibiotics present a promising solution for overcoming resistance in methicillin-resistant Staphylococcus aureus (MRSA). Previous studies have introduced iron as a novel coating for silver nanoparticles (AgNPs) to enhance both economic efficiency and potency against S. aureus. However, there are currently no available data on the potential of these novel nanostructures to reverse MRSA resistance. To address this gap, a population study was conducted within the MRSA community, collecting a total of 48 S. aureus isolates from skin lesions. Among these, 21 isolates (43.75%) exhibited cefoxitin resistance as determined by agar disk diffusion assay. Subsequently, a PCR test confirmed the presence of the mecA gene in 20 isolates, verifying them as MRSA. These results highlight the cefoxitin disk diffusion susceptibility test as an accurate screening method for predicting mecA-mediated resistance in MRSA. Synergy tests were performed on cefoxitin, serving as a marker antibiotic, and iron-coated AgNPs (Fe@AgNPs) in a combination study using the checkerboard assay. The average minimal inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) of cefoxitin were calculated as 11.55mg/mL and 3.61mg/mL, respectively. The findings indicated a synergistic effect (FIC index < 0.5) between Fe@AgNPs and cefoxitin against 90% of MRSA infections, while an additive effect (0.5 ≤ FIC index ≤ 1) could be expected in 10% of infections. These results suggest that Fe@AgNPs could serve as an economically viable candidate for co-administration with antibiotics to reverse resistance in MRSA infections within skin lesions. Such findings may pave the way for the development of future treatment strategies against MRSA infections.

Antimicrobial nanostructures: most potent structures, applications, and mechanism of action

Antimicrobial nanostructures: most potent structures, applications, and mechanism of action

Dual Species Bacterial Challenge of a Biomimetic Nanostructured Surface

AbstractAn ever‐present risk of medical device associated infection has driven a significant body of research toward development of novel anti‐infective materials. Surfaces bearing sharp nanostructures are an emerging technology to address this concern. The in vitro efficacy of antimicrobial nanostructures has previously been verified using single species cultures, but there remains a paucity of data to address the threat of infections containing more than one species. Polymicrobial infections are a concerning threat because they can complicate treatment, promote drug resistance, and harshen patient prognosis. In the present study, dual‐species cultures are employed to challenge the mechano‐bactericidal properties of nanostructured surfaces. Escherichia coli is used with either Staphylococcus aureus or Enterococcus faecalis due to their clinical relevance in implant associated infection. Despite the presence of two mixed species, a high rate of bactericidal activity is found. Interestingly, in the mixed culture containing Escherichia coli with Enterococcus faecalis, the nanostructured surface triggers a shift in species distribution to favor Enterococcus faecalis. Overall, this study highlights the potential for mechano‐bactericidal surfaces to minimize the burden of infections containing more than one species. It also serves as an enticing foundation for further research into more complex biointerfacial interactions.

Synthesis of mesoporous antimicrobial herbal nanomaterial-carrier for silver nanoparticles and antimicrobial sensing

Herbal nanoparticles (HNPs) were introduced as a novel generation of antimicrobial nanoparticles. But in the battle against superbugs we need nanostructures with boosted antimicrobial potency. So in the current experiment, for the first time a green approach was developed for the silver functionalization of HNPs which were fabricated from an antimicrobial herb Thymus vulgaris. Silver functionalized HNPs (AgHNPs) were found to be mesoporous and were further fortified with antimicrobial compounds. The resulted structures were re-tested against MRSA and P. aeruginosa as superbugs. It was found that silver functionalization can provide eight-fold increase in the antimicrobial potency of HNPs. Moreover, MIC was reduced from 20 mg/mL to 2.5 mg/mL. Another eight-fold reduction in the MIC (0.3 mg/mL) was achieved by fortification with antimicrobial compounds. So, the antimicrobial potency of HNPs was successfully increase approximately up to 64-folds. Obtained results illustrated that silver functionalization and fortification with antimicrobial compounds can be considered as effective approaches to achieve HNPs with boosted antimicrobial potency. These nanostructures have the potency to be loaded with other antimicrobial compound such as antibiotics toward synergistic effects of AgNPs and antibiotics. Resulted nanostructures can be employed in the formulation of powerful topical and surface disinfectants against superbugs. Also, these particles can be considered as a next generation of boosted antimicrobial nanostructures.

Facet-dependent antibacterial activity of Au nanocrystals

Engineered nanomaterials have attracted significantly attention as one of the most promising antimicrobial agents for against multidrug resistant infections. The toxicological responses of nanomaterials are closely related to their physicochemical properties, and establishment of a structure-activity relationship for nanomaterials at the nano-bio interface is of great significance for deep understanding antibacterial toxicity mechanisms of nanomaterials and designing safer antibacterial nanomaterials. In this study, the antibacterial behaviors of well-defined crystallographic facets of a series of Au nanocrystals, including {100}-facet cubes, {110}-facet rhombic dodecahedra, {111}-facet octahedra, {221}-facet trisoctahedra and {720}-facet concave cubes, was investigated, using the model bacteria Staphylococcus aureus. We find that Au nanocrystals display substantial facet-dependent antibacterial activities. The low-index facets of cubes, octahedra, and rhombic dodecahedra show considerable antibacterial activity, whereas the high-index facets of trisoctahedra and concave cubes remained inert under biological conditions. This result is in stark contrast to the previous paradigm that the high-index facets were considered to have higher bioactivity as compared with low-index facets. The antibacterial mechanism studies have shown that the facet-dependent antibacterial behaviors of Au nanocrystals are mainly caused by differential bacterial membrane damage as well as inhibition of cellular enzymatic activity and energy metabolism. The faceted Au nanocrystals are unique in that they do not induce generation of reactive oxygen species, as validated for most antibiotics and antimicrobial nanostructures. Our findings may provide a deeper understanding of facet-dependent toxicological responses and suggest the complexities of the nanomaterial-cell interactions, shedding some light on the development of high performance Au nanomaterials-based antibacterial therapeutics.

Bi2S3 coated Au nanorods for enhanced photodynamic and photothermal antibacterial activities under NIR light

Antimicrobial nanostructures are expected to be effective alternatives to antibiotics, combating the emergence of drug resistance and superbugs. Herein, we have developed an intermediate layer conversion strategy to fabricate urchin-shaped Au@Bi2S3 core-shell structures via a hard template engaged polyol method, which showed low cytotoxicity and excellent photothermal conversion properties. This metal-semiconductor composite nanostructures are also behaved as the typical Schottky junction that can improve the separation efficiency of the electron-hole pairs triggered by near-infrared (NIR) light, leading to considerable generation of reactive oxygen species (ROS). As a result, the obtained urchin-shaped Au@Bi2S3 core-shell structures exhibited enhanced antibacterial ability compared to Au nanorods or Bi2S3 alone, which can be attributed to the higher yield of ROS and hyperthermia. Once stimulated by 808 nm laser irradiation, urchin-shaped Au@Bi2S3 core-shell structures made a nearly 100% bactericidal ratio quickly for Escherichia coli (140 μg/mL) and Staphylococcus aureus (120 μg/mL) owing to their synergetic photothermal and photodynamic anti-bacterial (PTA/PDA) performance. Thus, this work can be extended to fabricate some other heterostructures comprised of semiconductors and metals/semiconductors. In particular, the urchin-shaped Au@Bi2S3 core-shell structures is a promising candidate for rapidly bacterial elimination in medical treatment or environmental remedy.

Antimicrobial Bilayer Nanocomposites Based on the Incorporation of As-Synthetized Hollow Zinc Oxide Nanotubes.

An antimicrobial polymeric bilayer structure based on the application of an acrylic coating containing hollow zinc oxide nanotubes over a polymeric substrate was developed in this work. Firstly, zinc oxide nanotubes (ZnONT) were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers followed by polymer removal through calcination with the purpose of obtaining antimicrobial nanostructures with a high specific area. Parameters of electrospinning, ALD, and calcination processes were set in order to obtain successfully hollow zinc oxide nanotubes. Morphological studies through scanning electron microscopy (SEM) and transmission electron microscopy (TEM) microscopies confirmed the morphological structure of ZnONT with an average diameter of 180 nm and thickness of approximately 60 nm. Thermal and X-ray diffraction (XRD) analyses provided evidence that calcination completely removed the polymer, resulting in a crystalline hexagonal wurtzite structure. Subsequently, ZnONT were incorporated into a polymeric coating over a polyethylene extruded film at two concentrations: 0.5 and 1 wt. % with respect to the polymer weight. An antimicrobial analysis of developed antimicrobial materials was performed following JIS Z2801 against Staphylococcus aureus and Escherichia coli. When compared to active materials containing commercial ZnO nanoparticles, materials containing ZnONT presented higher microbial inhibition principally against Gram-negative bacteria, whose reduction was total for films containing 1 wt. % ZnONT. Antiviral studies were also performed, but these materials did not present significant viral reduction.

Novel hollow titanium dioxide nanospheres with antimicrobial activity against resistant bacteria.

The search for and synthesis of new antimicrobial nanostructures is important to reduce microbial incidence that induces infectious diseases and to aid in the antibiotic resistance crisis, which are two of the most pressing issues in global public health. In this work, novel, hollow, calcined titanium dioxide nanospheres (CSTiO2) were successfully synthesized for the first time through the combination of electrospinning and atomic layer deposition techniques. Poly(vinylpyrrolidone) (PVP) electrosprayed spherical particles were double-coated with alumina and titanium dioxide, and after a calcination process, hollow nanospheres were obtained with a radius of approximately 345 nm and shell thickness of 17 nm. The structural characterization was performed using electron microscopy, and X-ray diffraction and small-angle X-ray diffraction evidenced an anatase titanium dioxide crystalline structure. Thermogravimetric analysis and Fourier-transform infrared spectroscopy studies demonstrated the absence of polymer residue after the calcination process. The antimicrobial properties of the developed CSTiO2 hollow nanospheres were evaluated against different bacteria, including resistant E. coli and S. aureus strains, and when compared to commercial TiO2 nanoparticles, CSTiO2 nanospheres exhibited superior performance. In addition, the positive effect of UV irradiation on the antimicrobial activity was demonstrated.

Evaluation of Biologic and Some Physical Properties of Flexible Resin Modified with Antimicrobial Nanostructures

Evaluation of Biologic and Some Physical Properties of Flexible Resin Modified with Antimicrobial Nanostructures

CuO and CeO2 Nanostructures Green Synthesized Using Olive Leaf Extract Inhibits the Growth of Highly Virulent Multidrug Resistant Bacteria.

One of the major challenges of nano-biotechnology is to engineer potent antimicrobial nanostructures (NS) with high biocompatibility. Keeping this in view, we have performed aqueous olive leaf extract mediated one pot facile synthesis of CuO-NS and CeO2-NS. Prepared NS were homogenous, less than 26 nm in size, and small crystallite units as revealed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Fourier transform infrared spectroscopy (FTIR) of CuO-NS and CeO2-NS showed typical Cu-O prints around 592–660 cm-1 and Ce-O bond vibrations at 453 cm-1. The successful capping of CuO-NS and CeO2-NS by compounds present in the plant extract was further validated by high performance liquid chromatography (HPLC) and thermal gravimetric analysis (TGA). Active phyto-chemicals from the leaf extract simultaneously acted as strong reducing as well as capping agent in the NS synthesis. NS engineered in the present study showed antibacterial potential at extremely low concentration against highly virulent multidrug-resistant (MDR) gram-negative strains (Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Pseudomonas aeruginosa), alarmed by World Health Organization (WHO). Furthermore, CuO-NS and CeO2-NS did not show any cytotoxicity on HEK-293 cell lines and Brine shrimp larvae indicating that the NS green synthesized in the present study are biocompatible.

Learning from Nature: Bioinspired Strategies Towards Antimicrobial Nanostructured Systems

Microbial contamination still remains a major issue of the modern era, due to the widespread of drug-resistant pathogens. This has prompted researchers to come up with novel antimicrobial systems that could overcome antibiotic-resistance. In this context, nature can provide inestimable source of inspiration to design high-performance multifunctional materials with potent activity against drug-resistant pathogens. Actually, integrating the bio-inspired-approach with nanotechnology can provide cutting-edge solutions for drug-resistant infections. In this context, this review will examine recent advances in the development of bio-inspired antimicrobial nanostructures. Advantages of bioinspired approach to nanomaterials over conventional routes have been highlighted. Generally, bionspired synthesis can be carried out either by mimicking the functions of natural materials/ structures or by mimicking the biological processes employed to produce substances or materials. The review provides an overview of both strategies as applied to the synthesis of inorganic, organic as well as hybrid nanostructures. Antimicrobial efficacy and biological properties of these systems have been highlighted. Antimicrobial and antibiofouling nanostructured surfaces are also discussed.

Novel Antimicrobial Titanium Dioxide Nanotubes Obtained through a Combination of Atomic Layer Deposition and Electrospinning Technologies.

The search for new antimicrobial substances has increased in recent years. Antimicrobial nanostructures are one of the most promising alternatives. In this work, titanium dioxide nanotubes were obtained by an atomic layer deposition (ALD) process over electrospun polyvinyl alcohol nanofibers (PVN) at different temperatures with the purpose of obtaining antimicrobial nanostructures with a high specific area. Electrospinning and ALD parameters were studied in order to obtain PVN with smallest diameter and highest deposition rate, respectively. Chamber temperature was a key factor during ALD process and an appropriate titanium dioxide deposition performance was achieved at 200 °C. Subsequently, thermal and morphological analysis by SEM and TEM microscopies revealed hollow nanotubes were obtained after calcination process at 600 °C. This temperature allowed complete polymer removal and influenced the resulting anatase crystallographic structure of titanium dioxide that positively affected their antimicrobial activities. X-ray analysis confirmed the change of titanium dioxide crystallographic structure from amorphous phase of deposited PVN to anatase crystalline structure of nanotubes. These new nanostructures with very large surface areas resulted in interesting antimicrobial properties against Gram-positive and Gram-negative bacteria. Titanium dioxide nanotubes presented the highest activity against Escherichia coli with 5 log cycles reduction at 200 μg/mL concentration.

Bioinspired hybrid eumelanin–TiO2antimicrobial nanostructures: the key role of organo–inorganic frameworks in tuning eumelanin's biocide action mechanism through membrane interaction

Intrinsic biocide efficacy of eumelanins can be markedly enhanced through a templated formation in the presence of a TiO2-sol, leading to hybrid TiO2–melanin nanostructures. However, mechanisms and processes behind biocide activity still remain poorly understood. This paper discloses the fundamental mechanism of action of these systems providing mechanistic information on their peculiar interaction with Escherichia coli strains. To this purpose biocide characterization is combined with Electron Paramagnetic Resonance (EPR) spectroscopy to investigate radical species produced by the hybrids as well as their interactions with Gram(−) external bacterial membranes. Experimental results indicate that TiO2 mediated eumelanin polymerization leads to a peculiar mechanism of action of hybrid nanostructures, whose strong interactions with bacterial membranes enhance the action of reactive oxygen species (ROS) produced by eumelanin degradation itself, also concurring with the final biocide action. These findings provide strategic information for the development of eumelanin-based systems with enhanced activity against drug-resistant strains.

ChemInform Abstract: Antibacterial Polymeric Nanostructures for Biomedical Applications

AbstractReview: 134 refs.

Overcoming multidrug resistance in microbials using nanostructures self-assembled from cationic bent-core oligomers.

Novel cationic molecules based on rigid terephthalamide-bisurea cores flanked by imidazolium moieties are described. In aqueous media, these compounds self-assemble into supramolecular nanostructures with distinct morphologies. The compound with optimal hydrophilic/hydrophobic balance displays potent antimicrobial activity and high selectivity towards clinically-isolated MRSA without inducing drug-resistance. These self-assembled cationic antimicrobial nanostructures show promise for the prevention and treatment of multidrug-resistant infections.

Melanin-templated rapid synthesis of silver nanostructures.

BackgroundAs a potent antimicrobial agent, silver nanostructures have been used in nanosensors and nanomaterial-based assays for the detection of food relevant analytes such as organic molecules, aroma, chemical contaminants, gases and food borne pathogens. In addition silver based nanocomposites act as an antimicrobial for food packaging materials. In this prospective, the food grade melanin pigment extracted from sponge associated actinobacterium Nocardiopsis alba MSA10 and melanin mediated synthesis of silver nanostructures were studied. Based on the present findings, antimicrobial nanostructures can be developed against food pathogens for food industrial applications.ResultsBriefly, the sponge associated actinobacterium N. alba MSA10 was screened and fermentation conditions were optimized for the production of melanin pigment. The Plackett-Burman design followed by a Box-Behnken design was developed to optimize the concentration of most significant factors for improved melanin yield. The antioxidant potential, reductive capabilities and physiochemical properties of Nocardiopsis melanin was characterized. The optimum production of melanin was attained with pH 7.5, temperature 35°C, salinity 2.5%, sucrose 25 g/L and tyrosine 12.5 g/L under submerged fermentation conditions. A highest melanin production of 3.4 mg/ml was reached with the optimization using Box-Behnken design. The purified melanin showed rapid reduction and stabilization of silver nanostructures. The melanin mediated process produced uniform and stable silver nanostructures with broad spectrum antimicrobial activity against food pathogens.ConclusionsThe melanin pigment produced by N. alba MSA10 can be used for environmentally benign synthesis of silver nanostructures and can be useful for food packaging materials. The characteristics of broad spectrum of activity against food pathogens of silver nanostructures gives an insight for their potential applicability in incorporation of food packaging materials and antimicrobials for stored fruits and foods.

Cationic antimicrobial polymers and their assemblies.

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.