Chemical Structure of Stabilizing Layers of Negatively Charged Silver Nanoparticles as an Effector of Shifts in Soil Bacterial Microbiome under Short-Term Exposure

Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part I. Influence of Synthesis Parameters, Characterization, and Biomedical Studies

This study explores the green synthesis of silver nanoparticles (AgNPs) using Cymbopogon citratus (lemongrass) extract as a reducing agent. Synthesis was confirmed by a color change (light yellow to dark brown) under optimal conditions: 1.50 mM silver nitrate, 3.5% v/v extract, at 100 °C, with a pH of 9, and for 60 min. The AgNPs exhibited spherical morphology, a hydrodynamic diameter of 135.41 ± 49.30 nm, a zeta potential of -29.9 ± 1.4 mV, crystalline structure, and minimal aggregation. AgNPs showed significant antibacterial activity, particularly at >20 µg/well, with the zones of inhibition varying by bacterial strain. In vitro studies demonstrated anti-inflammatory, antidiabetic (α-glucosidase and α-amylase inhibition), and antioxidant activities, with AgNPs outperforming plant extract and nearing standard efficacy at higher concentrations. Cyto-toxicity studies indicated that AgNPs and plant extract were less toxic than doxorubicin but exhibited concentration-dependent effects on cancerous and non-cancerous cells. Eco-toxicity assays revealed that AgNPs were less acutely toxic than controls but posed risks with prolonged exposure. This work highlights the eco-friendly synthesis of AgNPs and their potential in biomedical applications, demonstrating efficacy in antibacterial and antioxidant activities.

The Impact of Nanoparticles and Molecular Forms of TiO2 on the Rhizosphere of Plants in the Example of Common Wheat (Triticum aestivum L.)-Shifts in Microbiome Structure and Predicted Microbial Metabolic Functions

This study investigated the effects of various titanium nanoparticles (TiO2NPs) on the structure, function, and trophic levels of the wheat rhizobiome. In contrast to the typically toxic effects of small nanoparticles (~10 nm), this research focused on molecular TiO2 and larger nanoparticles, as follows: medium-sized (68 nm, NPs1) and large (>100 nm, NPs2). The results demonstrated significant yet diverse impacts of different TiO2 forms on the rhizosphere microbiota. Large TiO2NPs2 and molecular TiO2 adversely affected the bacteriobiome and mycobiome, leading to an increase in autotrophic microbial groups. In contrast, medium-sized TiO2NPs1 shifted the microbiome toward chemoheterotrophy, promoting plant growth-associated bacteria, fungal saprotrophs, and potential phytopathogens, suggesting a beneficial r-strategy within the rhizosphere. Other treatments induced oligotrophic conditions, resulting in a less flexible rhizobiome with diminished root associations but an increased abundance of Trichoderma spp. Structural modelling revealed that even minor changes in operational taxonomic units (OTUs) could significantly alter the microbiota's metabolic potential. These findings highlight the importance of further research to optimize nanoparticle applications for sustainable agriculture.

Evaluating the Antibacterial Potential of Distinct Size Populations of Stabilized Zinc Nanoparticles

Engineered nanoparticles are precisely synthesized to exploit unique properties conferred by their small size and high surface area for environmental, biomedical, and agricultural applications. While these physical properties dictate functionality, they can also have various intended and unintended implications for biological systems. Both the particle size and shape influence cellular uptake. Because of zinc's antibacterial properties and role as a plant micronutrient, polyvinylpyrrolidone stabilized zinc nanoparticles (ZnNP) were selected for this study. Four synthesis methods were tested to produce distinct size populations of polymer-coated ZnNP, and all utilized water as the solvent to promote sustainable, green chemistry. The antibacterial activity of ZnNP was assessed in two agriculturally relevant bacteria strains: Escherichia coli and Bacillus cereus. To further examine the effects of ZnNP on bacterial cells, reactive oxygen species (ROS) generation was measured via hydrogen peroxide (H2O2) production. The bacteria's incubation temperature was also altered to assess bacterial growth and susceptibility after exposure to ZnNP. The ZnNP from the smaller size population inhibited the most growth across bacterial strains, assays, and incubation temperatures. Increased antibacterial effects and ROS production were observed after incubation at a higher temperature. These results indicate that the deliberately designed nanoparticles are potentially valuable in microbial control and offer promising solutions for the future of healthy agricultural systems.

Not the Silver Bullet: Uncovering the Unexpected Limited Impacts of Silver-Containing Showerheads on the Drinking Water Microbiome

The incidence of waterborne disease outbreaks in the United States attributed to drinking water-associated pathogens that can cause infections in the immunocompromised DWPIs (e.g., Legionella pneumophila, nontuberculous mycobacteria (NTM), and Pseudomonas aeruginosa, among others) appears to be increasing. An emerging technology adopted to reduce DWPIs are point-of-use devices, such as showerheads that contain silver, a known antimicrobial material. In this study, we evaluate the effect of silver-containing showerheads on DWPI density and the broader microbiome in shower water under real-use conditions in a full-scale shower system, considering three different silver-modified showerhead designs: (i) silver mesh within the showerhead, (ii) silver-coated copper mesh in the head and hose, and (iii) silver-embedded polymer composite compared to conventional plastic and metal showerheads. We found no significant difference in targeted DWPI transcriptional activity in collected water across silver and nonsilver shower head designs. Yet, the presence of silver and how it was incorporated in the showerhead influenced the metal concentrations, microbial rare taxa, and microbiome functionality. Microbial dynamics were also influenced by the showerhead age (i.e., time after installation). The results of this study provide valuable information for consumers and building managers to consider when choosing a showerhead meant to reduce microorganisms in shower water.

Multidrug resistance and phylogenetic analyses of Pseudomonas aeruginosa based on the 16S rRNA gene of isolates recovered from clinical samples and their susceptibility to silver-nanoparticle

Background

Pseudomonas aeruginosa is a highly antimicrobial-resistant pathogen with a very narrow range of effective antibacterial agents. Therefore, finding alternative compounds is highly required, such as silver nanoparticles (AgNPs).

Aim

The current study was conducted to identify the multidrug resistance (MDR) profile and perform a phylogenetic analysis on P. aeruginosa isolates recovered from clinical samples (human, cows, cats, and fish) and to study their susceptibility to AgNPs.

Methods

40 samples were subjected to conventional cultivation and biochemical analyses to identify P. aeruginosa. Moreover, these isolates were tested for their antibiotic resistance profile and their response to AgNPs using disk diffusion methods. PCR and Sanger-based sequencing were performed using the 16S rRNA gene as a target.

Results

The results showed that all isolates were resistant to cefixime and sensitive to meropenem. Conversely, the AgNPs were effective in producing larger zones of inhibition. The PCR revealed amplification of the target, and the sequencing and phylogenetic tree of four isolates revealed close similarity with global human sequences from different regions.

Conclusion

The study reveals the MDR characteristics of P. aeruginosa. The isolates are highly susceptible to silver nanoparticles.

Metallic nanoparticle actions on the outer layer structure and properties of Bacillus cereus and Staphylococcus epidermidis

Although the antimicrobial activity of nanoparticles (NPs) penetrating inside the cell is widely recognised, the toxicity of large NPs (>10 nm) that cannot be translocated across bacterial membranes remains unclear. Therefore, this study was performed to elucidate the direct effects of Ag-NPs, Cu-NPs, ZnO-NPs and TiO2-NPs on relative membrane potential, permeability, hydrophobicity, structural changes within chemical compounds at the molecular level and the distribution of NPs on the surfaces of the bacteria Bacillus cereus and Staphylococcus epidermidis. Overall analysis of the results indicated the different impacts of individual NPs on the measured parameters in both strains depending on their type and concentration. B. cereus proved to be more resistant to the action of NPs than S. epidermidis. Generally, Cu-NPs showed the most substantial toxic effect on both strains; however, Ag-NPs exhibited negligible toxicity. All NPs had a strong affinity for cell surfaces and showed strain-dependent characteristic dispersion. ATR-FTIR analysis explained the distinctive interactions of NPs with bacterial functional groups, leading to macromolecular structural modifications. The results presented provide new and solid evidence for the current understanding of the interactions of metallic NPs with bacterial membranes.

The impact of various forms of silver nanoparticles on the rhizosphere of wheat (Triticum aestivum L.) - Shifts in microbiome structure and predicted microbial metabolic functions

The study investigated the effects of different silver nanoparticles (AgNPs) on the soil microbiome and wheat growth. For comparison purposes, a commercial fungicide and silver nitrate (AgNO3) were used. The results revealed three distinct groups of nanoparticles based on their impacts. Small-size AgNPs (10 nm) with a negative charge, as well as fungicide had limited effects on the microbiome, similar to the no-treatment control. Bigger in size (30-60 nm) and a negative charge AgNPs showed the most beneficial effects on soil microbiota shifts. These AgNPs increased the abundance of bacteria with beneficial traits such as nitrogen-fixing, urease, protease, and lignin degradation bacteria. The third type of AgNPs had a positive charge of nanostructure and influenced specific microbial populations, increasing the abundance of anaerobic and autotrophic groups of microorganisms, which could be assessed as a harmful shift for plants growth promotions and was similar to the AgNO3 treatment. Overall, the study emphasized the potential of AgNPs in agriculture not only as biocidal. The conducted study proved that AgNPs with bigger size/negative charge, used in low concentration can have a surprisingly stimulating effect on the positive characteristics of the rhizosphere microbiome. Moreover, the surface charge of AgNPs is a significant factor affecting microbial activity of wheat rhizosphere soil, which in this treatment is significantly similar to the AgNO3 treatment.

Nanosilver: An Old Antibacterial Agent with Great Promise in the Fight against Antibiotic Resistance

Antibiotic resistance in bacteria is a major problem worldwide that costs 55 billion USD annually for extended hospitalization, resource utilization, and additional treatment expenditures in the United States. This review examines the roles and forms of silver (e.g., bulk Ag, silver salts (AgNO3), and colloidal Ag) from antiquity to the present, and its eventual incorporation as silver nanoparticles (AgNPs) in numerous antibacterial consumer products and biomedical applications. The AgNP fabrication methods, physicochemical properties, and antibacterial mechanisms in Gram-positive and Gram-negative bacterial models are covered. The emphasis is on the problematic ESKAPE pathogens and the antibiotic-resistant pathogens of the greatest human health concern according to the World Health Organization. This review delineates the differences between each bacterial model, the role of the physicochemical properties of AgNPs in the interaction with pathogens, and the subsequent damage of AgNPs and Ag+ released by AgNPs on structural cellular components. In closing, the processes of antibiotic resistance attainment and how novel AgNP-antibiotic conjugates may synergistically reduce the growth of antibiotic-resistant pathogens are presented in light of promising examples, where antibiotic efficacy alone is decreased.

Silver Is Not Equal to Silver: Synthesis and Evaluation of Silver Nanoparticles with Low Biological Activity, and Their Incorporation into C12Alanine-Based Hydrogel

A new type of silver nanoparticles (AgNPs) was prepared and comprehensively studied. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) analyses indicated that 24 nm AgNPs with narrow size distribution were obtained while Z-potential confirms their good stability. The composites of the obtained AgNPs with nontoxic-nature-inspired hydrogel were formed upon cooling of the aqueous solution AgNPs and C₁₂Ala. The thermal gravimetric analysis (TGA) and the differential scanning calorimetry (DSC) do not show significant shifts in the characteristic temperature peaks for pure and silver-enriched gels, which indicates that AgNPs do not strongly interact with C₁₂Ala fibers, which was also confirmed by SEM. Both AgNPs alone and in the assembly with the gelator C₁₂Ala were almost biologically passive against bacteria, fungus, cancer, and nontumor human cells, as well as zebra-fish embryos. These studies proved that the new inactive AgNPs-doped hydrogels have potential for the application in therapy as drug delivery media.