A novel mechanism for the antibacterial effect of silver nanoparticles on Escherichia coli

Elucidating antibiofilm as well as photocatalytic disinfection potential of green synthesized nanosilver against multi-drug-resistant bacteria and its photodegradation ability of cationic dyes

BACKGROUND

Bioinspired nanomaterials have widely been employed as suitable alternatives for controlling biofilm and pathogens due to their distinctive physico-chemical properties.

METHODOLOGY

This study explored the antibiofilm as well as photocatalytic potential of silver (Ag) nanoparticles (NPs) synthesized using the cell-free supernatant of Lactobacillus acidophilus for the disinfection of multi-drug-resistant (MDR) strains of enteroaggregative E. coli (EAEC), Salmonella Typhimurium, S. Enteritidis and methicillin-resistant Staphylococcus aureus (MRSA) on exposure to LED light. In addition, the removal of toxic cationic dyes i.e., methylene blue (MB), rhodamine B (RhB) and crystal violet (CV) was explored on exposure to sunlight, LED and UV lights.

RESULTS

Initially, the synthesis of AgNPs was verified using UV- Vis spectroscopy, X-ray diffraction and transmission electron microscopy. The synthesized AgNPs exhibited MIC and MBC values of 7.80 and 15.625 µg/mL, respectively. The AgNPs exhibited significant inhibition (P < 0.001) in the biofilm-forming ability of all the tested MDR isolates. On exposure to LED light, the AgNPs could effectively eliminate all the tested MDR isolates in a dose-dependent manner. While performing photocatalytic assays, the degradation of RhB was observed to be quite slower than MB and CV irrespective of the tested light sources. Moreover, the sunlight as well as UV light exhibited better photodegradation capacity than LED light. Notwithstanding the light sources, RhB followed zero-order kinetics; however, MB and CV followed primarily second-order kinetics.

CONCLUSION

The green synthesized AgNPs were found to be an effective photocatalytic as well as antifouling candidate that could be applied in therapeutics and wastewater treatment.

A Comprehensive Review of Silver and Gold Nanoparticles as Effective Antibacterial Agents

The increasing threat from antibiotic-resistant bacteria has necessitated the development of novel methods to counter bacterial infections. In this context, the application of metallic nanoparticles (NPs), especially gold (Au) and silver (Ag), has emerged as a promising strategy due to their remarkable antibacterial properties. This review examines research published between 2006 and 2023, focusing on leading journals in nanotechnology, materials science, and biomedical research. The primary applications explored are the efficacy of Ag and Au NPs as antibacterial agents, their synthesis methods, morphological properties, and mechanisms of action. An extensive review of the literature on NPs synthesis, morphology, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and effectiveness against various Gram(+/-) bacteria confirms the antibacterial efficacy of Au and Ag NPs. The synthesis methods and characteristics of NPs, such as size, shape, and surface charge, are crucial in determining their antibacterial activity, as these factors influence their interactions with bacterial cells. Furthermore, this review underscores the urgent necessity of standardizing synthesis techniques, MICs, and reporting protocols to enhance the comparability and reproducibility of future studies. Standardization is essential for ensuring the reliability of research findings and accelerating the clinical application of NP-based antimicrobial approaches. This review aims to propel NP-based antimicrobial strategies by elucidating the properties that enhance the antibacterial activity of Ag and Au NPs. By highlighting their inhibitory effects against various bacterial strains and relatively low cytotoxicity, this work positions Ag and Au NPs as promising materials for developing antibacterial agents, making a significant contribution to global efforts to combat antibiotic-resistant pathogens.

Bacterial Electrophysiology

Bacterial ion fluxes are involved in the generation of energy, transport, and motility. As such, bacterial electrophysiology is fundamentally important for the bacterial life cycle, but it is often neglected and consequently, by and large, not understood. Arguably, the two main reasons for this are the complexity of measuring relevant variables in small cells with a cell envelope that contains the cell wall and the fact that, in a unicellular organism, relevant variables become intertwined in a nontrivial manner. To help give bacterial electrophysiology studies a firm footing, in this review, we go back to basics. We look first at the biophysics of bacterial membrane potential, and then at the approaches and models developed mostly for the study of neurons and eukaryotic mitochondria. We discuss their applicability to bacterial cells. Finally, we connect bacterial membrane potential with other relevant (electro)physiological variables and summarize methods that can be used to both measure and influence bacterial electrophysiology.

Silver and Copper Nanoparticle-Loaded Self-Assembled Pseudo-Peptide Thiourea-Based Organic-Inorganic Hybrid Gel with Antibacterial and Superhydrophobic Properties for Antifouling Surfaces

The escalating threat of antimicrobial resistance has become a global health crisis. Therefore, there is a rising momentum in developing biomaterials with self-sanitizing capabilities and inherent antibacterial properties. Despite their promising antimicrobial properties, metal nanoparticles (MNPs) have several disadvantages, including increased toxicity as the particle size decreases, leading to oxidative stress and DNA damage that need consideration. One solution is surface functionalization with biocompatible organic ligands, which can improve nanoparticle dispersibility, reduce aggregation, and enable targeted delivery to microbial cells. The existing research predominantly concentrates on the advancement of peptide-based hydrogels for coating materials to prevent bacterial infection, with limited exploration of developing surface coatings using organogels. Herein, we have synthesized organogel-based coatings doped with MNPs that can offer superior hydrophobicity, oleophobicity, and high stability that are not easily achievable with hydrogels. The self-assembled gels displayed distinct morphologies, as revealed by scanning electron microscopy and atomic force microscopy. The cross-linked matrix helps in the controlled and sustained release of MNPs at the site of bacterial infection. The synthesized self-assembled gel@MNPs exhibited excellent antibacterial properties against harmful bacteria such as Escherichia coli and Staphylococcus aureus and reduced bacterial viability up to 95% within 4 h. Cytotoxicity testing against metazoan cells demonstrated that the gels doped with MNPs were nontoxic (IC50 > 100 μM) to mammalian cells. Furthermore, in this study, we coated the organogel@MNPs on cotton fabric and tested it against Gram +ve and Gram -ve bacteria. Additionally, the developed cotton fabric exhibited superhydrophobic properties and developed a barrier that limits the interaction between bacteria and the surface, making it difficult for bacteria to adhere and colonize, which holds potential as a valuable resource for self-cleaning coatings.

EDTA enables to alleviate impacts of metal ions on conjugative transfer of antibiotic resistance genes

Various heavy metals are reported to be able to accelerate horizontal transfer of antibiotic resistance genes (ARGs). In real water environmental settings, ubiquitous complexing agents would affect the environmental behaviors of heavy metal ions due to the formation of metal-organic complexes. However, little is known whether the presence of complexing agents would change horizontal gene transfer due to heavy metal exposure. This study aimed to fill this gap by investigating the impacts of a typical complexing agent ethylenediaminetetraacetic acid (EDTA) on the conjugative transfer of plasmid-mediated ARGs induced by a range of heavy metal ions. At the environmentally relevant concentration (0.64 mg L-1) of metal ions, all the tested metal ions (Mg2+, Ca2+, Co2+, Pb2+, Ni2+, Cu2+, and Fe3+) promoted conjugative transfer of ARGs, while an inhibitory effect was observed at a relatively higher concentration (3.20 mg L-1). In contrast, EDTA (0.64 mg L-1) alleviated the effects of metal ions on ARGs conjugation transfer, evidenced by 11 %-66 % reduction in the conjugate transfer frequency. Molecular docking and dynamics simulations disclosed that this is attributed to the stronger binding of metal ions with the lipids in cell membranes. Under metal-EDTA exposure, gene expressions related to oxidative stress response, cell membrane permeability, intercellular contact, energy driving force, mobilization, and channels of plasmid transfer were suppressed compared with the metal ions exposure. This study offers insights into the alleviation mechanisms of complexing agents on ARGs transfer induced by free metal ions.

Rapid antibiotic screening based on E. coli apoptosis using a potentiometric sensor array

Phenotypic antimicrobial susceptibility testing enables reliable antibiotic screening but requires multiple strategies to identify each phenotypic change induced by different bactericidal mechanisms. Bacteria apoptosis with typical phenotypic features has never been explored for antibiotic screening. Herein, we developed an antibiotic screening method based on the measurement of antibiotic-induced phosphatidylserine (PS) exposure of apoptotic bacteria. Phosphatidylserine externalization of E. coli that can be widely used as an apoptosis marker for antibiotics with different antibacterial mechanisms was explored. A positively charged PS-binding peptide was immobilized on magnetic beads (MBs) to recognize and capture apoptotic E. coli with PS externalization. Apoptotic E. coli binding led to the charge or charge density change of MBs-peptide, resulting in a potential change on a magneto-controlled polymeric membrane potentiometric sensor. Based on the detection of apoptotic E. coli killed by antibiotics, antibiotic screening for different classes of antibiotics and silver nanoparticles was achieved within 1.5 h using a potentiometric sensor array. This approach enables sensitive, general, and time-saving antibiotic screening, and may open up a new path for antibiotic susceptibility testing.

Design and preparation of Ti-xFe antibacterial titanium alloys based on micro-area potential difference

Fe was selected as an alloying element for the first time to prepare a new antibacterial titanium alloy based on micro-area potential difference (MAPD) antibacterial mechanism. The microstructure, the corrosion resistance, the mechanical properties, the antibacterial properties and the cell biocompatibility have been investigated in detail by optical microscopy, scanning electron microscopy, electrochemical testing, mechanical property test, plate count method and cell toxicity measurement. It was demonstrated that heat treatment had a significant on the compressive mechanical properties and the antibacterial properties. Ti-xFe (x = 3,5 and 9) alloys after 850 °C/3 h + 550 °C/62 h heat treatment exhibited strong antimicrobial properties with an antibacterial rate of more than 90% due to the MAPD caused by the redistribution of Fe element during the aging process. In addition, the Fe content and the heat treatment process had a significant influence on the mechanical properties of Ti-xFe alloy but had nearly no effect on the corrosion resistance. All Ti-xFe alloys showed non-toxicity to the MC3T3 cell line in comparison with cp-Ti, indicating that the microzone potential difference had no adverse effect on the corrosion resistance, cell proliferation, adhesion, and spreading. Strong antibacterial properties, good cell compatibility and good corrosion resistance demonstrated that Ti-xFe alloy might be a candidate titanium alloy for medical applications.

Bactericidal Activity of Silver Nanoparticles on Oral Biofilms Related to Patients with and without Periodontal Disease

BACKGROUND AND OBJECTIVES

Periodontal disease (PD) is a multifactorial oral disease regularly caused by bacterial biofilms. Silver nanoparticles (AgNP) have offered good antimicrobial activity; moreover, there is no available scientific information related to their antimicrobial effects in biofilms from patients with PD. This study reports the bactericidal activity of AgNP against oral biofilms related to PD.

MATERIALS AND METHODS

AgNP of two average particle sizes were prepared and characterized. Sixty biofilms were collected from patients with (30 subjects) and without PD (30 subjects). Minimal inhibitory concentrations of AgNP were calculated and the distribution of bacterial species was defined by polymerase chain reaction.

RESULTS

Well-dispersed sizes of AgNP were obtained (5.4 ± 1.3 and 17.5 ± 3.4 nm) with an adequate electrical stability (-38.2 ± 5.8 and -32.6 ± 5.4 mV, respectively). AgNP showed antimicrobial activities for all oral samples; however, the smaller AgNP had significantly the most increased bactericidal effects (71.7 ± 39.1 µg/mL). The most resistant bacteria were found in biofilms from PD subjects (p < 0.05). P. gingivalis, T. denticola, and T. forsythia were present in all PD biofilms (100%).

CONCLUSIONS

The AgNP showed efficient bactericidal properties as an alternative therapy for the control or progression of PD.

Antimicrobial Activity of Green Synthesized Silver Nanoparticles Using Waste Leaves of Hyphaene thebaica (Doum Palm)

Silver nanoparticles (AgNPs) were biosynthesized for the first time from waste leaves extract of local doum palms in Tabuk, Saudi Arabia. The transmission electron microscope (TEM) revealed a spherical shape with a particle size from 18 to 33 nm. The d-spacing is about 2.6 Å, which confirms a face-centered cubic crystalline building. The biosynthesized AgNPs were evaluated as an antimicrobial agent against several pathogenic bacteria, including Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, and Pseudomonas aeruginosa ATCC 27853. The highest action was exerted against S. aureus ATCC 29213 (MIC = 1.5 µg/mL). Interestingly, AgNPs also showed anticandidal activity against the pathogenic yeasts Candida albicans ATCC 14053 (MIC = 24 µg/mL) and Candida tropicalis ATCC 13803 (MIC = 96 µg/mL). Scanning electron microscope (SEM) revealed deep morphological changes in Candida spp. due to the treatment of the AgNPs. Scarce pseudohyphae, perforation, exterior roughness, irregularly shaped cells, and production of protective exopolysaccharide (EPS) were the main features. In conclusion, the process of biosynthesis of AgNPs from the aqueous leaf extract of Hyphaene thebaica is environmentally compatible and induces the biosynthesis of tiny AgNPs that could be a promising candidate in biomedical applications, including antimicrobials against some pathogenic bacteria and yeasts.

Silver Nanoparticles Enhance the Antibacterial Effect of Antibiotic-Loaded Bone Cement

Purpose The goal of this study was to determine the antibacterial activity of bone cement in polymethyl methacrylate (PMMA) structures with varying amounts of silver nanoparticles (AgNPs) included. Additionally, we aimed to evaluate whether AgNPs affect the biomechanical properties of PMMA cement in our study. Materials and methods Between April 2020 and June 2020, we conducted a series of experiments to demonstrate the antibacterial characteristics by adding silver nanoparticles to PMMA bone cement. PMMA bone cement (Cemex, Tecres Company, Verona, Italy) was used as the base material. Seven different samples were prepared in order to evaluate the amount and presence of AgNPs. Cement samples containing AgNPs and teicoplanin at different concentrations and empty cement (control, without teicoplanin and AgNPs) were placed on Petri plates. The agar diffusion method was used to determine the antibacterial effect (Kirby-Bauer). Results Kirby-Bauer assays demonstrated that AgNPs added to bone cement increased the antimicrobial activity compared to antibiotic-free or only teicoplanin-loaded cement. It was observed that increasing the AgNPs ratio further increased the antimicrobial activity. Conclusion AgNPs in various combinations enhance antimicrobial activity synergistically while maintaining the mechanical strength of bone cement. Increasing the amount of AgNPs results in a significant increase in antimicrobial activity.

Copper-Based Compounds against Erwinia amylovora: Response Parameter Analysis and Suppression of Fire Blight in Apple

Fire blight, caused by Erwinia amylovora, is one of the major bacterial disease of apple and pear, causing enormous economic losses worldwide. Several control measures against E. amylovora have been reported till date, however, none of them have proved to be effective significantly against the pathogen. In this study, mechanisms of the copper-based control agents (CBCAs): copper oxychloride (COCHL), copper oxide (COX), copper hydroxide (CHY), copper sulfate basic (CSB), and tribasic copper sulfate (TCS) and their disease severity reduction efficacy against E. amylovora were analyzed. Bis-1,3-dibutylbarbituric acid trimethine oxonol, carboxyl fluorescein diacetate succinimidyl ester, and 5-cyano-2,3-ditolyl tetrazolium chloride staining were used to check the damage of membrane potential, cytoplasmic pHin, and respiration of CBCAs-treated E. amylovora, respectively. High disturbance in the membrane potential of E. amylovora was found under COX and COCHL treatments. Similarly, higher significant changes in the inner cytoplasmic pHin were observed under COX, COCHL, and TCS treatment. CHY and COCHL-treated E. amylovora showed a significant reduction in respiration. In vitro bioassay results revealed that CHY, CSB, and TCS at 2,000 ppm reduced the severity of fire blight both in pre- and post-treatment of CBCAs in immature apple fruits and seedlings. Overall, the most effective CBCAs against E. amylovora could be CHY at 2,000 ppm as its showed inhibition mechanisms and disease severity reduction.

Green Synthesis of Silver Nanoparticles Using Randia aculeata L. Cell Culture Extracts, Characterization, and Evaluation of Antibacterial and Antiproliferative Activity

The demand for metallic nanoparticles synthesized using green methods has increased due to their various therapeutic and clinical applications, and plant biotechnology may be a potential resource facilitating sustainable methods of AgNPs synthesis. In this study, we evaluate the capacity of extracts from Randia aculeata cell suspension culture (CSC) in the synthesis of AgNPs at different pH values, and their activity against pathogenic bacteria and cancer cells was evaluated. Using aqueous CSC extracts, AgNPs were synthesized with 10% (w/v) of fresh biomass and AgNO3 (1 mM) at a ratio of 1:1 for 24 h of incubation and constant agitation. UV-vis analysis showed a high concentration of AgNPs as the pH increased, and TEM analysis showed polydisperse nanoparticles with sizes from 10 to 90 nm. Moreover, CSC extracts produce reducing agents such as phenolic compounds (162.2 ± 27.9 mg gallic acid equivalent/100 g biomass) and flavonoids (122.07 ± 8.2 mg quercetin equivalent/100 g biomass). Notably, AgNPs had strong activity against E. coli, S. pyogenes, P. aeruginosa, S. aureus, and S. typhimurium, mainly with AgNPs at pH 6 (MIC: 1.6 to 3.9 µg/mL). AgNPs at pH 6 and 10 had a high antiproliferative effect on cancer cells (IC50 < 5.7 µg/mL). Therefore, the use of cell suspension cultures may be a sustainable option for the green synthesis of AgNPs.

Green synthesis of silver nanoparticles and their antibacterial effects

Antibacterial resistance is by far one of the greatest challenges to global health. Many pharmaceutical or material strategies have been explored to overcome this dilemma. Of these, silver nanoparticles (AgNPs) are known to have a non-specific antibacterial mechanism that renders it difficult to engender silver-resistant bacteria, enabling them to be more powerful antibacterial agents than conventional antibiotics. AgNPs have shown promising antibacterial effects in both Gram-positive and Gram-negative bacteria. The aim of this review is to summarize the green synthesis of AgNPs as antibacterial agents, while other AgNPs-related insights (e.g., antibacterial mechanisms, potential toxicity, and medical applications) are also reviewed.

Biogenic biocompatible silver nanoparticles: a promising antibacterial agent

The biogenic synthesis of silver nanoparticles (AgNPs) are gaining attention because they are eco-friendly, non-hazardous, economical and devoid of the drawbacks of physicochemical processes. Biogenic approaches for synthesizing nanoparticles (NPs) using plant leaves, seeds, bark, stems, fruits, roots and flowers are highly cost-effective compared to other methods. Silver (Ag) has been used since ancient times, but biogenic AgNPs have only been made in the last few decades. They have been employed primarily in the food and pharmaceutical industries as antimicrobials and antioxidants. Recent studies have confirmed that many molecules present in different bacteria, including Escherichia coli, Staphylococcus aureus, Citrobacter koseri, Bacillus cereus, Salmonella typhi, Klebsipneumoniaoniae, Vibrio parahaemolyticus, Pseudomonas Aeruginosa, are bound to the AgNPs and can be inhibited using multifaceted mechanisms like AgNPs inter inside the cells, free radicals, ROS generation and modulate transduction pathways. Recent breakthroughs in nanobiotechnology-based therapeutics have opened up new possibilities for fighting microorganisms. Thus, in particular, biogenic AgNPs as powerful antibacterial agents have gained much interest. Surface charge, colloidal state, shape, concentration and size are the most critical physicochemical characteristics that determine the antibacterial potential of AgNPs. Based on this review, it can be stated that AgNPs could be made better in terms of their potency, durability, accuracy, biosecurity and compatibility.

Anti-Adherence and Antimicrobial Activities of Silver Nanoparticles against Serotypes C and K of Streptococcus mutans on Orthodontic Appliances

Background and Objectives: Streptococcus mutans (S. mutans) is the main microorganism associated with the presence of dental caries and specific serotypes of this bacteria have been related to several systemic diseases limiting general health. In orthodontics, white spot lesions (WSL), represent a great challenge for clinicians due to the great fluctuation of their prevalence and incidence during conventional orthodontic treatments. Although silver nanoparticles (AgNP) have been demonstrated to have great antimicrobial properties in several microorganisms, including S. mutans bacteria, there is no available information about anti adherence and antimicrobial properties of AgNP exposed to two of the most relevant serotypes of S. mutans adhered on orthodontic materials used for conventional therapeutics. The objective of this study was to determine anti-adherence and antimicrobial levels of AgNP against serotypes c and k of S. mutans on conventional orthodontic appliances. Materials and Methods: An AgNP solution was prepared and characterized using dispersion light scattering (DLS) and transmission electron microscopy (TEM). Antimicrobial and anti-adherence activities of AgNP were determined using minimal inhibitory concentrations (MIC) and bacterial adherence testing against serotypes c and k of S. mutans clinically isolated and confirmed by PCR assay. Results: The prepared AgNP had spherical shapes with a good size distribution (29.3 ± 0.7 nm) with negative and well-defined electrical charges (−36.5 ± 5.7 mV). AgNP had good bacterial growth (55.7 ± 19.3 µg/mL for serotype c, and 111.4 ± 38.6 µg/mL for serotype k) and adherence inhibitions for all bacterial strains and orthodontic wires (p < 0.05). The serotype k showed statistically the highest microbial adherence (p < 0.05). The SS wires promoted more bacterial adhesion (149.0 ± 253.6 UFC/mL × 104) than CuNiTi (3.3 ± 6.0 UFC/mL × 104) and NiTi (101.1 ± 108.5 UFC/mL × 104) arches. SEM analysis suggests CuNiTi wires demonstrated better topographical conditions for bacterial adherence while AFM evaluation determined cell wall irregularities in bacterial cells exposed to AgNP. Conclusions: This study suggests the widespread use of AgNP as a potential anti-adherent and antimicrobial agent for the prevention of WSL during conventional orthodontic therapies and, collaterally, other systemic diseases.

Streptomyces catenulae as a Novel Marine Actinobacterium Mediated Silver Nanoparticles: Characterization, Biological Activities, and Proposed Mechanism of Antibacterial Action

Biosynthesized silver nanoparticles (Bio-SNPs) were synthesized from the marine actinobacterium strain Streptomyces catenulae M2 and characterized using a variety of techniques, including UV–vis spectrum, fourier transform infrared spectroscopy (FTIR), energy dispersive x-ray (EDX), transmission electron microscopy (TEM), dynamic light scattering (DLS), surface-enhanced Raman spectroscopy (SERS), and zeta potential. The antibacterial activity of Bio-SNPs alone and in combination with antibiotic was evaluated using a microtiter-dilution resazurin assay against multidrug-resistant (MDR) bacteria. Bio-SNPs’ minimum inhibitory concentration (MIC) against bacterial strains was determined. To assess the synergistic effect of Bio-SNPs in combination with antibiotics, the Fractional Inhibitory Concentration Index (FICI) was calculated. While the safety of Bio-SNPs in biomedical applications is dependent on their use, the in vitro cytotoxicity of Bio-SNPs on normal human epithelial colon cells (NCM460) and human colorectal adenocarcinoma cells (CaCo2) were evaluated using the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay and cell lactate dehydrogenase (LDH) release. The presence of Bio-SNPs was revealed by UV–vis spectroscopy, which revealed a peak in the Surface Plasmon Resonance (SPR) spectrum at 439.5 nm. Bio-SNPs were spherical in shape and small in size (average 33 nm by TEM, 58.8 nm by DLS), with good stability (−30 mV) and the presence of capping agents. Bio-SNPs had MIC values ranging from 2 to 64 μg/ml against the bacteria tested. The MIC for P. aeruginosa was the lowest (2 μg/ml). Antibiotics have been shown to have a significant synergistic effect when combined with Bio-SNPs against tested bacteria. Bio-SNPs exhibited dose-dependent cytotoxicity against NCM460 and CaCo2 cancer cells, with the latter exhibiting far greater toxicity than  the  former.  NCM460  and CaCo2  cell   viability   decreased   from  99.3 to 95.7% and 92.3 to 61.8%, respectively, whereas LDH leakage increased from 200 to 215 nmol/ml and 261 to 730 nmol/ml, respectively. The half inhibitory concentrations (IC₅₀) for NCM460 and CaCo2 cancer cells were 79.46 and 10.41 μg/ml and 89.4 and 19.3 μg/ml, respectively. Bio-SNPs were found to be biocompatible and to have anti-inflammatory activity. Bio-SNPs are highly appealing for future nanomedicine applications due to their antibacterial and biocompatible properties and their inherent “green” and simple manufacturing.

Green synthesis of silver nanoparticles and its antibacterial activity using fungus Talaromyces purpureogenus isolated from Taxus baccata Linn

The present study is focused on the synthesis of silver nanoparticles (AgNPs) utilizing endophytic fungus Talaromyces purpureogenus, isolated from Taxus baccata Linn. Extracellular extract of Talaromyces purpureogenus has shown occurrence of secondary metabolites viz. terpenoids and phenols. Gas chromatography-mass spectroscopy analysis showed the presence of 16 compounds. Techniques like Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, field emission gun scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction were employed to characterize the synthesized AgNPs. UV–Vis spectroscopy showed sharp peaks at 380–470 nm which indicates the presence of metallic silver. FTIR analysis showed the presence of various functional groups like phenols, hydroxyl groups, and primary amines. In DLS, Z-average size and PdI of synthesized AgNPs were 240.2 r.nm and 0.720 respectively, with zeta potential − 19.6 mV. In FEG-SEM and HRTEM the spherical AgNPs showed diameter in the range of 30–60 nm. In EDS analysis the weight percent of Ag is 67.26% and atomic percent is 43.13%. From XRD analysis the size of AgNPs was found to be 49.3 nm with face-centered cubic crystalline nature of fungal synthesized AgNPs. These nanoparticles have shown significant antibacterial activity against tested strains viz. Listeria monocytogenes (13 ± 0.29 mm), Escherichia coli (17 ± 0.14 mm), Shigella dysenteriae (18 ± 0.21 mm) and Salmonella typhi (14 ± 0.13 mm). These synthesized AgNPs have shown effective free radical scavenging activity against 2,2′-diphenyl-1-picrylhydrazyl. The present study showed that the endophytic fungus Talaromyces purpureogenus can be used as a prominent source to synthesize AgNPs by using biological, ecofriendly, and in a non-toxic way accompanied by antibacterial and antioxidant properties which further can reduce the harvesting pressure faced by Taxus baccata.

Graphical Abstract

Photochemical Synthesis of Silver Hydrosol Stabilized by Carbonate Ions and Study of Its Bactericidal Impact on Escherichia coli: Direct and Indirect Effects

The great attention paid to silver nanoparticles is largely related to their antibacterial and antiviral effects and their possible use as efficient biocidal agents. Silver nanoparticles are being widely introduced into various areas of life, including industry, medicine, and agriculture. This leads to their spreading and entering the environment, which generates the potential risk of toxic effect on humans and other biological organisms. Proposed paper describes the preparation of silver hydrosols containing spherical metal nanoparticles by photochemical reduction of Ag+ ions with oxalate ions. In deaerated solutions, this gives ~10 nm particles, while in aerated solutions, ~20 nm particles with inclusion of the oxide Ag2O are obtained. Nanoparticles inhibit the bacterium Escherichia coli and suppress the cell growth at concentrations of ~1 × 10-6-1 × 10-4 mol L-1. Silver particles cause the loss of pili and deformation and destruction of cell membranes. A mechanism of antibacterial action was proposed, taking into account indirect suppressing action of Ag+ ions released upon the oxidative metal dissolution and direct (contact) action of nanoparticles on bacterial cells, resulting in a change in the shape and destruction of the bacteria.

Nano-silver functionalized polysaccharides as a platform for wound dressings: A review

The healing of defected skin tissue is a complex process, especially for chronic wounds. Poor healing of these wounds may cause extensive suffering and high cost for patients. Traditional wound dressings are typically designed for a single function and they cannot satisfy all requirements for the whole process of wound healing. Therefore, it is necessary to develop new types of wound dressings with multiple functions for wound healing. In particular, adding an antibacterial function has been shown to be of great benefit during tissue repair. Nano‑silver is widely used in wound treatment because of various advantages, such as its wide antibacterial spectrum and lower drug resistance. Therefore, wound dressings loaded with nano‑silver have attracted widespread attention in wound healing. Naturally derived polysaccharides hold great potential as wound dressings, because of their abundant availability, low prices and good biocompatibility. In this review, nano‑silver functionalized polysaccharide-based wound dressings are systematically reviewed, including their preparation methods, antibacterial performances and classification of nano‑silver wound dressings. Moreover, the toxicity of nano‑silver based wound dressings is discussed and the prospective research direction is elaborated. This review aims to provide readers with an overview of the latest developments in silver nanotechnology, and to provide a little guidance for the research of nano‑silver functionalized polysaccharide-based wound dressings.

Hyaluronic Acid-Silver Nanocomposites and Their Biomedical Applications: A Review

For the last years scientific community has witnessed a rapid development of novel types of biomaterials, which properties made them applicable in numerous fields of medicine. Although nanosilver, well-known for its antimicrobial, anti-angiogenic, anti-inflammatory and anticancer activities, as well as hyaluronic acid, a natural polysaccharide playing a vital role in the modulation of tissue repair, signal transduction, angiogenesis, cell motility and cancer metastasis, are both thoroughly described in the literature, their complexes are still a novel topic. In this review we introduce the most recent research about the synthesis, properties, and potential applications of HA-nanosilver composites. We also make an attempt to explain the variety of mechanisms involved in their action. Finally, we present biocompatible and biodegradable complexes with bactericidal activity and low cytotoxicity, which properties suggest their suitability for the prophylaxis and therapy of chronic wounds, as well as analgetic therapies, anticancer strategies and the detection of chemical substances and malignant cells. Cited studies reveal that the usage of hyaluronic acid-silver nanocomposites appears to be efficient and safe in clinical practice.

An NIR-Triggered Au Nanocage Used for Photo-Thermo Therapy of Chronic Wound in Diabetic Rats Through Bacterial Membrane Destruction and Skin Cell Mitochondrial Protection

Bacterial infection and its severe oxidative stress reaction will cause damage to skin cell mitochondria, resulting in long-lasting wound healing and great pain to patients. Thus, delayed wound healing in diabetic patients with Staphylococcus aureus infection is a principal challenge worldwide. Therefore, novel biomaterials with multifunction of bacterial membrane destruction and skin cell mitochondrial protection are urgently needed to be developed to address this challenge. In this work, novel gold cage (AuNCs) modified with epigallocatechin gallate (EGCG) were prepared to treat delayed diabetic wounds. The results showed that Au-EGCG had a high and stable photothermal conversion efficiency under near-infrared irradiation, and the scavenging rate of Au-EGCG for S. aureus could reach 95%. The production of large amounts of reactive oxygen species (ROS) leads to the disruption of bacterial membranes, inducing bacterial lysis and apoptosis. Meanwhile, Au-EGCG fused into hydrogel (Au-EGCG@H) promoted the migration and proliferation of human umbilical cord endothelial cells, reduced cellular mitochondrial damage and oxidative stress in the presence of infection, and significantly increased the basic fibroblast growth factor expression and vascular endothelial growth factor. In addition, animal studies showed that wound closure was 97.2% after 12 days of treatment, and the healing of chronic diabetic wounds was significantly accelerated. Au-EGCG nanoplatforms were successfully prepared to promote cell migration and angiogenesis in diabetic rats while removing S. aureus, reducing oxidative stress in cells, and restoring impaired mitochondrial function. Au-EGCG provides an effective, biocompatible, and multifunctional therapeutic strategy for chronic diabetic wounds.

The membrane depolarization and increase intracellular calcium level produced by silver nanoclusters are responsible for bacterial death

This work highlights how our silver ultra nanoclusters (ARGIRIUM-SUNc) hand-made synthesized, are very useful as a bactericide and anti-biofilm agent. The Argirium-SUNc effective antibacterial concentrations are very low (< 1 ppm) as compared to the corresponding values reported in the literature. Different bacterial defense mechanisms are observed dependent on ARGIRIUM-SUNc concentrations. Biochemical investigations (volatilome) have been performed to understand the pathways involved in cell death. By using fluorescence techniques and cell viability measurements we show, for the first time, that membrane depolarization and calcium intracellular level are both primary events in bacteria death. The ARGIRIUM-SUNc determined eradication of different biofilm at a concentration as low as 0.6 ppm. This suggests that the effect of the nanoparticles follows a common mechanism in different bacteria. It is highly probable that the chemical constitution of the crosslinks could be a key target in the disrupting mechanism of our nanoparticles. Since the biofilms and their constituents are essential for bacterial survival in contact with humans, the silver nanoparticles represent a logical target for new antibacterial treatments.

Biogenic Silver Nanoparticles: What We Know and What Do We Need to Know?

Nanobiotechnology is considered to be one of the fastest emerging fields. It is still a relatively new and exciting area of research with considerable potential for development. Among the inorganic nanomaterials, biogenically synthesized silver nanoparticles (bio-AgNPs) have been frequently used due to their unique physicochemical properties that result not only from their shape and size but also from surface coatings of natural origin. These properties determine antibacterial, antifungal, antiprotozoal, anticancer, anti-inflammatory, and many more activities of bio-AgNPs. This review provides the current state of knowledge on the methods and mechanisms of biogenic synthesis of silver nanoparticles as well as their potential applications in different fields such as medicine, food, agriculture, and industries.

Recent Advances Toward the Use of Mesoporous Silica Nanoparticles for the Treatment of Bacterial Infections

It is a fact that the use of antibiotics is inducing a growing resistance on bacteria. This situation is not only the consequence of a drugs’ misuse, but a direct consequence of a widespread and continuous use. Current studies suggest that this effect could be reversed by using abandoned antibiotics to which bacteria have lost their resistance, but this is only a temporary solution that in near future would lead to new resistance problems. Fortunately, current nanotechnology offers a new life for old and new antibiotics, which could have significantly different pharmacokinetics when properly delivered; enabling new routes able to bypass acquired resistances. In this contribution, we will focus on the use of porous silica nanoparticles as functional carriers for the delivery of antibiotics and biocides in combination with additional features like membrane sensitizing and heavy metal-driven metabolic-disrupting therapies as two of the most interesting combination therapies.

Biospectroscopy and chemometrics as an analytical tool for comparing the antibacterial mechanism of silver nanoparticles with popular antibiotics against Escherichia coli

Despite the fact that silver nanoparticles (AgNPs) have been widely studied in medical and correlated fields, details on their mechanisms are yet to be fully understood. Herein we present the first study on the combination of infrared spectroscopy and chemometrics as an analytical tool to investigate the mechanism of action of AgNPs against Escherichia coli by comparison with popular and commercially available antibiotics. The rationale behind this study is that the selected antibiotics act on bacteria in specific and distinct manners (DNA, cell membrane, mitochondria, etc.). Hence, via multivariate analysis we were able to compare the spectra of bacteria treated with the antibiotics and AgNPs to determine the main target of the latter. Spectral comparison, exploratory analysis, clustering and classification based on infrared spectra were carried out for E. coli samples in the absence and presence (treated) of four widely known antibiotics (ampicillin, ciprofloxacin, gentamicin and sulfadiazine) as well as RA-AgNPs and ERA-AgNPs. Chemometrics models indicated an interesting similarity between infrared spectra from E. coli treated with sulfadiazine and AgNPs, in which vibrational modes associated to phosphate groups were found to be the most representative. This result suggests that both AgNPs and sulfadiazine affects DNA structural features and availability, but not necessarily through the same mechanism. This biospectroscopy-based approach opens an interesting possibility for the understanding over the mechanism of antibacterial activity of AgNPs.

Green Synthesized Silver Nanoparticles: Antibacterial and Anticancer Activities, Biocompatibility, and Analyses of Surface-Attached Proteins

The increasing number of multi-drug-resistant bacteria and cancer cases, that are a real threat to humankind, forces research world to develop new weapons to deal with it. Biogenic silver nanoparticles (AgNPs) are considered as a solution to this problem. Biosynthesis of AgNPs is regarded as a green, eco-friendly, low-priced process that provides small and biocompatible nanostructures with antimicrobial and anticancer activities and potential application in medicine. The biocompatibility of these nanoparticles is related to the coating with biomolecules of natural origin. The synthesis of AgNPs from actinobacterial strain was confirmed using UV-Vis spectroscopy while their morphology, crystalline structure, stability, and coating were characterized using, transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential and Fourier transform infrared spectroscopy (FTIR). Antibacterial activity of biogenic AgNPs was evaluated by determination of minimum inhibitory and minimum biocidal concentrations (MIC and MBC) against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. The potential mechanism of antibacterial action of AgNPs was determined by measurement of ATP level. Since the use of AgNPs in biomedical applications depend on their safety, the in vitro cytotoxicity of biosynthesized AgNPs on MCF-7 human breast cancer cell line and murine macrophage cell line RAW 264.7 using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, cell lactate dehydrogenase (LDH) release and measurement of reactive oxygen species (ROS) level were assessed. The nanoparticle protein capping agent that can be involved in reduction of silver ions to AgNPs and their stabilization was identified using LC-MS/MS. Nanoparticles were spherical in shape, small in size (mean 13.2 nm), showed crystalline nature, good stability (-18.7 mV) and presence of capping agents. They exhibited antibacterial activity (MIC of 8-128 μg ml^-1, MBC of 64-256 μg ml^-1) and significantly decreased ATP levels in bacterial cells after treatment with different concentrations of AgNPs. The in vitro analysis showed that the AgNPs demonstrated dose-dependent cytotoxicity against RAW 264.7 macrophages and MCF-7 breast cancer cells but higher against the latter than the former. Cell viability decrease was found to be 42.2-14.2 and 38.0-15.5% while LDH leakage 14.6-42.7% and 19.0-45.0%, respectively. IC₅₀ values calculated for MTT assay was found to be 16.3 and 12.0 μg ml^-1 and for LDH assay 102.3 and 76.2 μg ml^-1, respectively. Moreover, MCF-7 cells released a greater amount of ROS than RAW 264.7 macrophages during stimulation with all tested concentrations of AgNPs (1.47-3.13 and 1.02-2.58 fold increase, respectively). The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis revealed the presence of five protein bands at a molecular weight between 31.7 and 280.9 kDa. These proteins showed the highest homology to hypothetical proteins and porins from E. coli, Delftia sp. and Pseudomonas rhodesiae. Based on obtained results it can be concluded that biogenic AgNPs were capped with proteins and demonstrated potential as antimicrobial and anticancer agent.

Green Synthesized Silver Nanoparticles: Antibacterial and Anticancer Activities, Biocompatibility, and Analyses of Surface-Attached Proteins

The increasing number of multi-drug-resistant bacteria and cancer cases, that are a real threat to humankind, forces research world to develop new weapons to deal with it. Biogenic silver nanoparticles (AgNPs) are considered as a solution to this problem. Biosynthesis of AgNPs is regarded as a green, eco-friendly, low-priced process that provides small and biocompatible nanostructures with antimicrobial and anticancer activities and potential application in medicine. The biocompatibility of these nanoparticles is related to the coating with biomolecules of natural origin. The synthesis of AgNPs from actinobacterial strain was confirmed using UV-Vis spectroscopy while their morphology, crystalline structure, stability, and coating were characterized using, transmission electron microscopy (TEM), X-ray diffraction (XRD), Zeta potential and Fourier transform infrared spectroscopy (FTIR). Antibacterial activity of biogenic AgNPs was evaluated by determination of minimum inhibitory and minimum biocidal concentrations (MIC and MBC) against Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. The potential mechanism of antibacterial action of AgNPs was determined by measurement of ATP level. Since the use of AgNPs in biomedical applications depend on their safety, the in vitro cytotoxicity of biosynthesized AgNPs on MCF-7 human breast cancer cell line and murine macrophage cell line RAW 264.7 using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, cell lactate dehydrogenase (LDH) release and measurement of reactive oxygen species (ROS) level were assessed. The nanoparticle protein capping agent that can be involved in reduction of silver ions to AgNPs and their stabilization was identified using LC-MS/MS. Nanoparticles were spherical in shape, small in size (mean 13.2 nm), showed crystalline nature, good stability (-18.7 mV) and presence of capping agents. They exhibited antibacterial activity (MIC of 8-128 μg ml-1, MBC of 64-256 μg ml-1) and significantly decreased ATP levels in bacterial cells after treatment with different concentrations of AgNPs. The in vitro analysis showed that the AgNPs demonstrated dose-dependent cytotoxicity against RAW 264.7 macrophages and MCF-7 breast cancer cells but higher against the latter than the former. Cell viability decrease was found to be 42.2-14.2 and 38.0-15.5% while LDH leakage 14.6-42.7% and 19.0-45.0%, respectively. IC50 values calculated for MTT assay was found to be 16.3 and 12.0 μg ml-1 and for LDH assay 102.3 and 76.2 μg ml-1, respectively. Moreover, MCF-7 cells released a greater amount of ROS than RAW 264.7 macrophages during stimulation with all tested concentrations of AgNPs (1.47-3.13 and 1.02-2.58 fold increase, respectively). The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis revealed the presence of five protein bands at a molecular weight between 31.7 and 280.9 kDa. These proteins showed the highest homology to hypothetical proteins and porins from E. coli, Delftia sp. and Pseudomonas rhodesiae. Based on obtained results it can be concluded that biogenic AgNPs were capped with proteins and demonstrated potential as antimicrobial and anticancer agent.

Review on Silver Nanoparticles as a Novel Class of Antibacterial Solutions

Nanomaterials represent a promising novel class of materials to be used as antibacterial solutions. Inhomogeneity of synthesis and characterization methods, as well as resulting variate physical and chemical properties make selection of proper nanostructure difficult when designing antimicrobial experiments. Present study focuses on the already existing evidence regarding silver nanoparticles and their antibacterial applications, with focus on various modulatory factors of reported antimicrobial efficiency. Present paper focuses on synthesis and characterization methods, factors modulating antibacterial efficiency, laboratory quantification procedures, as well as up–to-date knowledge on mechanisms of antibacterial action for silver nanoparticles. Moreover, challenges and future prospects for antimicrobial applications of silver nanoparticles are reviewed and discussed.

Silver nanoparticles-induced H2O2 triggers apoptosis-like death and is associated with dinF in Escherichia coli

Silver nanoparticles (AgNPs) are the most widely used nanomaterials as antimicrobial agents. AgNPs have been shown to inhibit the growth of and induce apoptosis-like death in Escherichia coli. However, the precise mechanism of AgNPs-induced apoptosis-like death and association with DNA damage-inducible protein F (dinF), a gene of SOS response, is unknown. Here, AgNPs-contributing depletion of intracellular glutathione levels and deactivation of glutathione peroxidase were shown. This step, indicating disruption of the antioxidant system, resulted in overall oxidative stress. Furthermore, DNA oxidation was accompanied, leading to DNA fragmentation. In addition, AgNPs appeared to induce apoptosis-like death via the SOS response. We used sodium pyruvate - an H₂O₂ quencher - to study the contribution of H₂O₂, which showed attenuation of AgNPs-induced DNA damage, SOS response, and apoptosis-like death. In dinF mutant, the strain showed a higher degree of DNA damage and apoptotic features. In conclusion, AgNPs mediate apoptosis-like cell death by H₂O₂-induced oxidative DNA damage. Furthermore, our result demonstrates that dinF participates in this process, which further supports that AgNPs induces SOS response. Our findings may contribute to expanding the new applications of AgNP-based nanomaterials in biomedical fields.

Biomedical Applications of Reactive Oxygen Species Generation by Metal Nanoparticles

The design, synthesis and characterization of new nanomaterials represents one of the most dynamic and transversal aspects of nanotechnology applications in the biomedical field. New synthetic and engineering improvements allow the design of a wide range of biocompatible nanostructured materials (NSMs) and nanoparticles (NPs) which, with or without additional chemical and/or biomolecular surface modifications, are more frequently employed in applications for successful diagnostic, drug delivery and therapeutic procedures. Metal-based nanoparticles (MNPs) including metal NPs, metal oxide NPs, quantum dots (QDs) and magnetic NPs, thanks to their physical and chemical properties have gained much traction for their functional use in biomedicine. In this review it is highlighted how the generation of reactive oxygen species (ROS), which in many respects could be considered a negative aspect of the interaction of MNPs with biological matter, may be a surprising nanotechnology weapon. From the exchange of knowledge between branches such as materials science, nanotechnology, engineering, biochemistry and medicine, researchers and clinicians are setting and standardizing treatments by tuning ROS production to induce cancer or microbial cell death.

Ångstrom-scale silver particle-embedded carbomer gel promotes wound healing by inhibiting bacterial colonization and inflammation

Poor wound healing after diabetes or extensive burn remains a challenging problem. Recently, we presented a physical approach to fabricate ultrasmall silver particles from Ångstrom scale to nanoscale and determined the antitumor efficacy of Ångstrom-scale silver particles (AgÅPs) in the smallest size range. Here we used the medium-sized AgÅPs (65.9 ± 31.6 Å) to prepare carbomer gel incorporated with these larger AgÅPs (L-AgÅPs-gel) and demonstrated the potent broad-spectrum antibacterial activity of L-AgÅPs-gel without obvious toxicity on wound healing-related cells. Induction of reactive oxygen species contributed to L-AgÅPs-gel-induced bacterial death. Topical application of L-AgÅPs-gel to mouse skin triggered much stronger effects than the commercial silver nanoparticles (AgNPs)-gel to prevent bacterial colonization, reduce inflammation, and accelerate diabetic and burn wound healing. L-AgÅPs were distributed locally in skin without inducing systemic toxicities. This study suggests that L-AgÅPs-gel represents an effective and safe antibacterial and anti-inflammatory material for wound therapy.

A new Ag-nanostructured hydroxyapatite porous scaffold: Antibacterial effect and cytotoxicity study

We report a new chemical method for the functionalization of Mg-hydroxyapatite (Mg-HA) scaffold with Ag nanoparticles (Ag NPs) integrating in one step both the synthesis of the Ag NPs and their nano-structuring into the HA matrix (Ag-Mg-HA scaffold). This method exploits a green photochemical synthesis and allows the direct growth of Ag NPs on the Mg-HA surface. The surface structure of Ag-Mg-HA scaffold, investigated by scanning electron microscopy, shows no significant changes in the morphology upon Ag NPs incorporation. The presence of Ag was confirmed by EDX analysis. TEM and spectroscopic investigations show Ag NPs spherical shaped with a mean diameter of about 20 nm exhibiting the typical plasmon absorption band with maximum at 420 nm. The antibacterial properties of Ag-Mg-HA scaffolds were tested against two bacterial strains, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The results show excellent antibacterial properties achieving up to 99% and 100% reduction of colonies for both bacteria cultures after 24 h of incubation and 100% of reduction after 48 h of incubation. The cytotoxicity of Ag-Mg-HA was also in deep investigated assessing both cell proliferation and differentiation using hADSCs (human Adipose Derived Stem Cells) and testing data point at 0, 7, 14 and 24 days. The results show cytotoxic effect with cell proliferation decreasing up to 90% at 24 days and osteogenic differentiation inhibition. The observed cytotoxicity can be probable ascribed to the oxidative stress by ROS. Indeed, considering the effectiveness of the nanofunctionalization method and the excellent antibacterial properties showed by the Ag-Mg-HA scaffold, future works will be devoted to create nanofunctionalized scaffold satisfying both antimicrobial and osteo-regenerative properties.

Biogenic Silver Nanoparticles: Assessment of Their Cytotoxicity, Genotoxicity and Study of Capping Proteins

The development of nanotechnology in the last two decades has led to the use of silver nanoparticles (AgNPs) in various biomedical applications, including antimicrobial, anti-inflammatory, and anticancer therapies. However, the potential of the medical application of AgNPs depends on the safety of their use. In this work, we assessed the in vitro cytotoxicity and genotoxicity of silver nanoparticles and identified biomolecules covering AgNPs synthesized from actinobacterial strain SH11. The cytotoxicity of AgNPs against MCF-7 human breast cancer cell line and murine macrophage cell line RAW 264.7 was studied by MTT assay, cell LDH (lactate dehydrogenase) release, and the measurement of ROS (reactive oxygen species) level while genotoxicity in Salmonella typhimurium cells was testing using the Ames test. The in vitro analysis showed that the tested nanoparticles demonstrated dose-dependent cytotoxicity against RAW 264.6 macrophages and MCF-7 breast cancer cells. Moreover, biosynthesized AgNPs did not show a mutagenic effect of S. typhimurium. The analyses and identification of biomolecules present on the surface of silver nanoparticles showed that they were associated with proteins. The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis revealed the presence of 34 and 43 kDa protein bands. The identification of proteins performed by using LC-MS/MS (liquid chromatography with tandem mass spectrometry) demonstrated their highest homology to bacterial porins. Capping biomolecules of natural origin may be involved in the synthesis process of AgNPs or may be responsible for their stabilization. Moreover, the presence of natural proteins on the surface of bionanoparticles eliminates the postproduction steps of capping which is necessary for chemical synthesis to obtain the stable nanostructures required for application in medicine.

Both silver ions and silver nanoparticles facilitate the horizontal transfer of plasmid-mediated antibiotic resistance genes

Antibiotic resistance in bacteria is a growing threat to global human health. Horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) is recognized as the primary contributor to antibiotic resistance dissemination. Silver nanoparticles (AgNPs) are widely used in personal care products as antimicrobial agents. While heavy metals are known to induce antibiotic resistance in bacteria, it is not known whether AgNPs in the environment can stimulate the HGT of ARGs. Here, we report that both AgNPs and ionic silver Ag⁺, at environmentally relevant and sub-lethal concentrations, facilitate the conjugative transfer of plasmid-borne ARGs across bacterial genera (from the donor Escherichia coli K-12 LE392 to the recipient Pseudomonas putida KT2440). The underlying mechanisms of the Ag⁺- or AgNPs-promoted HGT were unveiled by detecting oxidative stress and cell membrane permeability, combined with genome-wide RNA sequencing and proteomic analyses. It was found that both Ag⁺ and AgNPs exposure induced various bacterial responses that included reactive oxygen species (ROS) generation, membrane damage and the SOS response. This study exposes the potential ecological risks of environmental levels of AgNPs and Ag⁺ for promoting the spread of ARGs and highlights concerns regarding the management of nanoparticles and heavy metals.

Advances in Magnetic Noble Metal/Iron-Based Oxide Hybrid Nanoparticles as Biomedical Devices

The study of the noble metal magnetic hybrid nanoparticles is a really promising topic from both the scientific and the technological points of views, with applications in several fields. Iron oxide materials which are hybridized with noble metal nanoparticles (NPs) have attracted increasing interest among researchers because of their cooperative effects on combined magnetic, electronic, photonic, and catalytic activities. This review article contains a summary of magnetic noble metal/iron oxide nanoparticle systems potentially useful in practical biomedical applications. Among the applications, engineered devices for both medical diagnosis and treatments were considered. The preparation to produce different structures, as blends or core-shell structures, of several nanometric systems was also considered. Several characterization techniques available to describe the structure, morphology and different kinds of properties of hybrid nanoparticles are also included in this review.

Biosynthesized silver nanoparticles: Decoding their mechanism of action in Staphylococcus aureus and Escherichia coli

The oxidative stress generation in bacteria by the presence of antibiotics (in this case silver nanoparticles (AgNPs)) is already widely known. Previously, we demonstrated that AgNPs generate oxidative stress in Staphylococcus aureus and Escherichia coli mediated by the increase of reactive oxygen species (ROS). In this work we are demonstrating the consequences of the oxidative stress by the presence of AgNPs; these bacterial strains increased the levels of oxidized proteins and lipids. In addition, it was possible to determine which reactive oxygen species are mainly responsible for the oxidative damage to macromolecules. Also, we found that the bacterial DNA was fragmented and the membrane potential was modified. This increase in the levels of ROS found in both, S. aureus and E. coli, was associated with the oxidation of different types of important macromolecules for the normal functioning of cell, so the oxidative stress would be one of the mechanisms by which the AgNPs would exert their toxicity in both strains, one Gram positive and the other Gram negative of great clinical relevance.

Review of the effects of silver nanoparticle exposure on gut bacteria

Gut bacteria are involved in regulating several important physiological functions in the host, and intestinal dysbacteriosis plays an important role in several human diseases, including intestinal, metabolic and autoimmune disorders. Although silver nanoparticles (AgNPs) are increasingly being incorporated into medical and consumer products due to their unique physicochemical properties, studies have indicated their potential to affect adversely the gut bacteria. In this review, we focus on the biotoxicological effects of AgNPs entering the gastrointestinal tract and the relationship of these effects with important nanoscale properties. We discuss in detail the mechanisms underlying the bactericidal toxicity effects of AgNPs and explore the relationships between AgNPs, gut bacteria and disease. Finally, we highlight the need to focus on the negative effects of AgNPs usage to facilitate appropriate development of these particles.

Potential antibacterial mechanism of silver nanoparticles and the optimization of orthopedic implants by advanced modification technologies

Infection, as a common postoperative complication of orthopedic surgery, is the main reason leading to implant failure. Silver nanoparticles (AgNPs) are considered as a promising antibacterial agent and always used to modify orthopedic implants to prevent infection. To optimize the implants in a reasonable manner, it is critical for us to know the specific antibacterial mechanism, which is still unclear. In this review, we analyzed the potential antibacterial mechanisms of AgNPs, and the influences of AgNPs on osteogenic-related cells, including cellular adhesion, proliferation, and differentiation, were also discussed. In addition, methods to enhance biocompatibility of AgNPs as well as advanced implants modifications technologies were also summarized.