Interaction of silver nanoparticles with serum proteins affects their antimicrobial activity in vivo

Layer-by-layer films of polysaccharides modified with polyethylene glycol and dextran

Layer-by-layer (LbL) films with enhanced resistance to protein adsorption were obtained on the basis of N-grafted copolymers of chitosan with polyethylene glycol (PEG) or dextran (DEX). The copolymers with the backbone molecular weight of 18 and 450 kDa, side chains of PEG of 5.0 and 0.9 kDa, DEX of 6.0 kDa and the degree of amine groups substitution χ_Sub as high as ∼0.25 were alternated with dextran sulfate (DS) to assemble up to 10 bilayer films. The film material contains 85±5% of water with virtually no effect of the copolymer structure. By utilizing the graft copolymers and applying suitable number of copolymer/DS bilayers to the surface, the mass of adsorbed fetal bovine serum proteins was decreased by 70-85% as compared to that on unmodified chitosan/DS film. In terms of overlapping side chains on the LbL surface the copolymers of PEG and DEX are equally effective in tailoring protein-resistant materials.

Silver nanoparticles as antimicrobial therapeutics: current perspectives and future challenges

Utility of silver metal in antimicrobial therapy is an accepted practice since ages that faded with time because of the identification of a few silver resistant strains in the contemporary era. A successive development of antibiotics soon followed. However, due to an indiscriminate and unregulated use coupled with poor legal control measures and a dearth of expertise in handling the critical episodes, the antibiotics era has already seen a steep decline in the past decades due to the evolution of multi-drug resistant 'superbugs' which pose a sizeable challenge to manage with. Due to limited options in the pipeline and no clear strategy in the forefront, the aspirations for novel, MDR focused drug discovery to target the 'superbugs' arose which once again led to the rise of AgNPs in antimicrobial research. In this review, we have focused on the green routes for the synthesis of AgNPs, the mode of microbial inhibition by AgNPs, synergistic effect of AgNPs with antibiotics and future challenges for the development of nano-silver-based therapeutics.

Superior Bactericidal Efficacy of Fucose-Functionalized Silver Nanoparticles against Pseudomonas aeruginosa PAO1 and Prevention of Its Colonization on Urinary Catheters

Pseudomonas aeruginosa, a Gram-negative rod-shaped bacterium is a notorious pathogen causing chronic infections. Its ability to form antibiotic-resistant biofilm has raised the need for the development of alternative treatment approaches. An ideal alternate can be silver nanoparticles known for their strong yet tunable bactericidal activity. However, their use in commercial in vivo medicine could not see the light of the day because of the unwanted toxicity of silver in the host cells at higher concentrations. Thus, strategies which can modulate the bacterial cell-silver nanoparticle interactions thereby reducing the amount of nanoparticles required to kill a typical number of bacterial cells are utmost welcomed. The current work showcases one such strategy by functionalizing the silver nanoparticles with l-fucose to increase their interactions with the LecB lectins present on P. aeruginosa PAO1. The advantage of this approach lies in the higher bactericidal and antibiofilm activity of fucose-functionalized silver nanoparticles (FNPs) as compared to the citrate-capped silver nanoparticles (CNPs) of similar size and concentrations. The superior bactericidal potential of FNPs as demonstrated by fluorescence-assisted cell sorting, confocal laser scanning microscopy, and transmission electron microscopy analyses may be attributed to the higher reactive oxygen species generation and oxidative membrane damage. Additionally, FNPs prevented the formation of biofilms by downregulating the expression of various virulence genes at lower concentrations as compared to CNPs. The practical applicability of the approach was demonstrated by preventing bacterial colonization on artificial silicone rubber surfaces. These results can be extrapolated in the treatment of catheter-associated urinary tract infections caused by P. aeruginosa. In conclusion, the present work strongly advocates the use of antivirulence targets and their corresponding binding residues for the augmentation of the bactericidal effect of silver nanoparticles.

Evaluation of E. coli inhibition by plain and polymer-coated silver nanoparticles

Escherichia coli causes various ailments such as septicemia, enteritis, foodborne illnesses, and urinary tract infections which are of concern in the public health field due to antibiotic resistance. Silver nanoparticles (AgNP) are known for their biocompatibility and antibacterial activity, and may prove to be an alternative method of treatment, especially as wound dressings. In this study, we compared the antibacterial efficacy of two polymer-coated silver nanoparticles either containing 10% Ag (Ag 10% + Polymer), or 99% Ag (AgPVP) in relation to plain uncoated silver nanoparticles (AgNP). Atomic force microscopy was used to characterize the nanoparticles, and their antibacterial efficacy was compared by the minimum inhibitory concentration (MIC) and bacterial growth curve assays, followed by molecular studies using scanning electron microscopy (SEM) and (qRT- PCR). AgNP inhibited the growth of E. coli only at 0.621 mg/mL, which was double the concentration required for both coated nanoparticles (0.312 mg/mL). Similarly, bacterial growth was impeded as early as 8 h at 0.156 mg/mL of both coated nanoparticles as compared to 0.312 mg/mL for plain AgNP. SEM data showed that nanoparticles damaged the cell membrane, resulting in bacterial cell lysis, expulsion of cellular contents, and complete disintegration of some cells. The expression of genes associated with the TCA cycle (aceF and frdB) and amino acid metabolism (gadB, metL, argC) were substantially downregulated in E. coli treated with nanoparticles. The reduction in the silver ion (Ag+) concentration of polymer-coated AgNP did not affect their antibacterial efficacy against E. coli.

Nanomaterial–microbe cross-talk: physicochemical principles and (patho)biological consequences

NPs’ characteristics impact their spontaneous binding to microbes, which may affect the (patho)biological identity of both NP and microbes.

Enhancing the antimicrobial and antibiofilm effectiveness of silver nanoparticles prepared by green synthesis

Water soluble catechin oligomers produce small (8.5 nm) silver nanoparticles with high antimicrobial and antibiofilm efficacy.

A new strategy for battling bacterial resistance: Turning potent, non-selective and potentially non-resistance-inducing biocides into selective ones

Antibiotic alternatives are in great need for combating antibiotic resistance. Selective delivery of a potent non-selective non-resistance-inducing biocide (C17) to MRSA was achieved by encapsulating it in solid lipid nanoparticles (SLNs) conjugated with a MRSA-specific antibody (termed as "Ab"). The C17-loaded Ab-conjugated SLNs (C17-SLN-Ab) demonstrated significantly better antimicrobial activity than its antibody free counterpart (C17-loaded SLN) and C17-loaded SLN with a non-specific IgG antibody. In a new MRSA/fibroblast co-culture assay, C17-SLN-Ab showed selective toxicity toward MRSA than fibroblast cells. C17-SLN-Ab possesses double selectivity, exhibiting higher toxicity to MRSA than to Pseudomonas aeruginosa. This same strategy was used to successfully increase C17's selectivity against E. coli K12 by switching the conjugated anti-MRSA antibody to an anti-E. coli antibody, demonstrating versatility of this new strategy. This proof-of-concept research can be extended to other non-selective antimicrobials, against which bacterial resistance is unlikely to develop, to generate a new group of promising antibiotic alternatives.

Potentiation of Tobramycin by Silver Nanoparticles against Pseudomonas aeruginosa Biofilms

Increasing antibiotic resistance among pathogenic bacterial species is a serious public health problem and has prompted research examining the antibacterial effects of alternative compounds and novel treatment strategies. Compounding this problem is the ability of many pathogenic bacteria to form biofilms during chronic infections. Importantly, these communities are often recalcitrant to antibiotic treatments that show effectiveness against acute infection. The antimicrobial properties of silver have been known for decades, but recently silver and silver-containing compounds have seen renewed interest as antimicrobial agents for treating bacterial infections. The goal of this study was to assess the ability of citrate-capped silver nanoparticles (AgNPs) of various sizes, alone and in combination with the aminoglycoside antibiotic tobramycin, to inhibit established Pseudomonas aeruginosa biofilms. Our results demonstrate that smaller 10-nm and 20-nm AgNPs were more effective at synergistically potentiating the activity of tobramycin. Visualization of biofilms treated with combinations of 10-nm AgNPs and tobramycin reveals that the synergistic bactericidal effect may be caused by disrupting cellular membranes. Minimum biofilm eradication concentration (MBEC) assays using clinical P. aeruginosa isolates shows that small AgNPs are more effective than larger AgNPs at inhibiting biofilms, but that the synergy effect is likely a strain-dependent phenomenon. These data suggest that small AgNPs synergistically potentiate the activity of tobramycin against P. aeruginosain vitro and may reveal a potential role for AgNP/antibiotic combinations in treating patients with chronic infections in a strain-specific manner.

Non-cytotoxic effect of green synthesized silver nanoparticles and its antibacterial activity

Silver nanoparticles (AgNPs) were green synthesized using ethanolic extract of fenugreek leaves and characterized using UV-Vis spectroscopy, Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), high resolution transmission electron microscopy HRTEM and energy dispersive X-ray analysis (EDX) techniques. The HRTEM results revealed the formation of highly stable, mono dispersed, spherical shaped AgNPs with the size ranging from 20 to 30nm. The presence of flavonoids and their interaction with the AgNPs were confirmed using FTIR. Antibacterial activities of the AgNPs were studied against pathogenic gram-positive Staphylococcus aureus (S. aureus) and gram negative Escherichia coli (E. coli) bacteria. The synthesized AgNPs displayed the enhancement of antibacterial activity against E. coli. The morphological changes in the bacterial cell membrane was observed using SEM analysis. Leakage of protein from the bacterial cells increased at every time intervals (2 and 4h). MTT assay was carried out for the AgNPs against human skin cell line (HaCaT). Interestingly, cytotoxicity of the synthesized AgNPs was less toxic to HaCaT cells as compared to bacteria cells, which suggests that the synthesized AgNPs by this method is eco-friendly in nature.

Polyvinylpyrrolidone-Capped Silver Nanoparticle Inhibits Infection of Carbapenem-Resistant Strain of Acinetobacter baumannii in the Human Pulmonary Epithelial Cell

Acinetobacter baumannii, an opportunistic ESKAPE pathogen, causes respiratory and urinary tract infections. Its prevalence increases gradually in the clinical setup. Pathogenicity of Acinetobacter is significantly influenced by its ability to infect and survive in human pulmonary cells. Therefore, it is important to study the infection of A. baumannii in human pulmonary host cell (A-549), monitoring surface interacting and internalized bacteria. It was found that during infection of A. baumannii, about 40% bacteria adhered to A-549, whereas 20% got internalized inside pulmonary cell and induces threefold increase in the reactive oxygen species production. We have synthesized polyvinylpyrrolidone (PVP)-capped AgNPs using chemical methods and tested its efficacy against carbapenem-resistant strain of A. baumannii. PVP-capped silver nanoparticles (PVP-AgNPs) (30 µM) have shown antibacterial activity against carbapenem-resistant strain of A. baumannii and this concentration does not have any cytotoxic effect on the human pulmonary cell line (IC₅₀ is 130 µM). Similarly, PVP-AgNPs treatment decreases 80% viability of intracellular bacteria, decreases adherence of A. baumannii to A-549 (40 to 2.2%), and decreases intracellular concentration (20 to 1.3%) of A. baumannii. This concludes that PVP-AgNPs can be developed as a substitute for carbapenem to control the infection caused by carbapenem-resistant A. baumannii.

Green synthesis of silver nanoparticles using Mentha pulegium and investigation of their antibacterial, antifungal and anticancer activity

A simple and eco-friendly method for efficient synthesis of stable colloidal silver nanoparticles (AgNPs) using Mentha pulegium extracts is described. A series of reactions was conducted using different types and concentrations of plant extract as well as metal ions to optimize the reaction conditions. AgNPs were characterized by using UV-vis spectroscopy, transmission electron microscopy, atomic force microscopy, dynamic light scattering, zetasizer, energy-dispersive X-ray spectroscopy (EDAX) and Fourier transform infrared spectroscopy (FTIR). At the optimized conditions, plate shaped AgNPs with zeta potential value of -15.7 and plasmon absorption maximum at 450 nm were obtained using high concentration of aqueous extract. Efficient adsorption of organic compounds on the nanoparticles was confirmed by FTIR and EDAX. The biogenic AgNPs displayed promising antibacterial activity on Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. The highest antibacterial activity of 25 µg mL-1 was obtained for all the strains using aqueous extract synthesized AgNPs. The aqueous extract synthesised AgNPs also showed considerable antifungal activity against fluconazole resistant Candida albicans. The cytotoxicity assay revealed considerable anticancer activity of AgNPs on HeLa and MCF-7 cancer cells. Overall results indicated high potential of M. pulegium extract to synthesis high quality AgNPs for biomedical applications.

Silver Nanoparticles Mediated by Costus afer Leaf Extract: Synthesis, Antibacterial, Antioxidant and Electrochemical Properties

Synthesis of metallic and semiconductor nanoparticles through physical and chemical routes has been extensively reported. However, green synthesized metal nanoparticles are currently in the limelight due to the simplicity, cost-effectiveness and eco-friendliness of their synthesis. This study explored the use of aqueous leaf extract of Costus afer in the synthesis of silver nanoparticles (CA-AgNPs). The optical and structural properties of the resulting silver nanoparticles were studied using UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red spectrophotometer (FTIR). TEM images of the silver nanoparticles confirmed the existence of monodispersed spherical nanoparticles with a mean size of 20 nm. The FTIR spectra affirmed the presence of phytochemicals from the Costus afer leaf extract on the surface of the silver nanoparticles. The electrochemical characterization of a CA-AgNPs/multiwalled carbon nanotubes (MWCNT)-modified electrode was carried out to confirm the charge transfer properties of the nanocomposites. The comparative study showed that the CA-AgNPs/MWCNT-modified electrode demonstrated faster charge transport behaviour. The anodic current density of the electrodes in Fe(CN)₆]4-/[Fe(CN)₆]3- redox probe follows the order: GCE/CA-Ag/MWCNT (550 mA/cm²) > GCE/MWCNT (270 mA/cm²) > GCE (80 mA/cm²) > GCE/CA-Ag (7.93 mA/cm²). The silver nanoparticles were evaluated for their antibacterial properties against Gram negative (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa) and Gram positive (Bacillus subtilis and Staphylococcus aureus) pathogens. The nanoparticles exhibited better inhibition of the bacterial strains compared to the precursors (leaf extract of Costus afer and silver nitrate). Furthermore, the ability of the nanoparticles to scavenge DPPH radicals at different concentrations was studied using the DPPH radical scavenging assay and compared to that of the leaf extract and ascorbic acid. The nanoparticles were better DPPH scavengers compared to the leaf extract and their antioxidant properties compared favorably the antioxidant results of ascorbic acid. The green approach to nanoparticles synthesis carried out in this research work is simple, non-polluting, inexpensive and non-hazardous.

Ultra-small silver nanoparticles induced ROS activated Toll-pathway against Staphylococcus aureus disease in silkworm model

The present study investigated the therapeutic action of flavonoids loaded silver nanoparticles (FLV-Ag NPs) on a silkworm, Bombyx mori L., larvae infected by the S. aureus, where an in vivo model system was used. FLV-Ag NPs were synthesized using a Ricinus communis L. leaf extracted flavonoid mixture in various concentrations. The reduction reaction was performed under a simple sunlight exposure condition. In the reduction process, quercetin and kaempferol loadings were also found. They were confirmed by UV-visible, TEM, XRD, XPS, DLS and FTIR spectroscopic techniques. TEM confirmed that the synthesized NPs were monodispersed and with an average size of 5.8nm±0.04. Initially, those synthesized FLV-Ag NPs were tested against S. aureus in in vitro by comparing their potential inhibitory activity with only flavonoids mixture (FLVs) and pure silver nanoparticles (Ag NPs). Furthermore, these FLV-Ag NPs were used to treat S. aureus infected B. mori larvae and the therapeutic efficacy was measured. Our results demonstrate that the FLV-Ag NPs are effective in curing the S. aureus infection through the induced expression of antimicrobial peptide genes, the enhanced oxidative enzyme levels, and the promoted phagocytosis of S. aureus by the haemocytes in silkworm larvae. On the basis of these results, it is proposed that the mechanism of the antimicrobial activity of FLV-Ag NPs involves the NPs-insect fat body cell association and a reactive oxygen species-mediated Toll-pathway.

How can nanoparticles contribute to antituberculosis therapy?

Therapeutic approaches using nanoparticles are being successfully used in foods and in several fields of medicine, including infectious diseases. Regarding tuberculosis (TB) treatment, nanoparticles can be a useful strategy for two distinct applications: (i) for their intrinsic antimycobacterial activity; (ii) as vehicles for known antitubercular drugs to allow reduction of dose- and drug-associated side-effects and administration via user-friendly administration routes such as pulmonary or oral ones. Promising results were obtained in vitro and in animal Mycobacterium tuberculosis models and need now to be translated into clinical drug candidates. Such a prospect can provide an opportunity regarding the current limited therapeutic options for drug-resistant TB and the scarcity of novel antituberculosis drugs in the drug discovery pipeline.

Converting a Natural Protein Compartment into a Nanofactory for the Size-Constrained Synthesis of Antimicrobial Silver Nanoparticles

Engineered biological systems are used extensively for the production of high value and commodity organics. On the other hand, most inorganic nanomaterials are still synthesized via chemical routes. By engineering cellular compartments, functional nanoarchitectures can be produced under environmentally sustainable conditions. Encapsulins are a new class of microbial nanocompartments with promising applications in nanobiotechnology. Here, we engineer the Thermotoga maritima encapsulin EncTm to yield a designed compartment for the size-constrained synthesis of silver nanoparticles (Ag NPs). These Ag NPs exhibit uniform shape and size distributions as well as long-term stability. Ambient aqueous conditions can be used for Ag NP synthesis, while no reducing agents or solvents need to be added. The antimicrobial activity of the synthesized protein-coated or shell-free Ag NPs is superior to that of silver nitrate and citrate-capped Ag NPs. This study establishes encapsulins as an engineerable platform for the synthesis of biogenic functional nanomaterials.

Antimicrobial properties of biosynthesized silver nanoparticles studied by flow cytometry and related techniques

This work reports the effect of silver bionanoparticles (Bio(AgNPs) synthesized by Actinobacteria CGG 11n on selected Gram (+) and Gram (-) bacteria. Flow cytometry, classical antibiogram method and fluorescent microscopy approach was used for evaluation of antimicrobial activity of Bio(AgNPs) and their combination with antibiotics. Furthermore, the performed research specified the capacity of flow cytometry method as an alternative to the standard ones and as a complementary method to electromigration techniques. The study showed antibacterial activity of both BioAgNPs and the combination of antibiotics/BioAgNPs against all the tested bacteria strains in comparison with a diffusion, dilution and bioautographic methods. The synergistic effect of antibiotics/BioAgNPs combination (e.g. kanamycin, ampicillin, neomycin and streptomycin) was found to be more notable against Pseudomonas aeruginosa representing a prototype of multi-drug resistant "superbugs" for which effective therapeutic options are very limited.

Photo-induced biosynthesis of silver nanoparticles from aqueous extract of Dunaliella salina and their anticancer potential

The synthesis of silver nanoparticles (AgNPs) via green route, using biological entities is an area of interest, because one of the potential applications in the nanomedicine. In the present study, we have developed photo-induced, ecofriendly, low cost method for biosynthesis of the stable silver nanoparticles using aqueous extract of Dunaliella salina (AED) which act as both reducing as well as stabilizing agent. Biosynthesis of the AgNPs was optimized as: sunlight exposure (30min), AED (5% (v/v)) and AgNO₃ (4mM). Biosynthesis of AgNPs was monitored by using UV-Vis spectroscopy which exhibited sharp SPR band at 430nm after 30min of bright sunlight exposure. SEM and TEM analyses confirmed the presence of spherical AgNPs with average size of 15.26nm. Crystalline nature of AgNPs was confirmed by SAED and XRD analyses where Braggs reflection pattern at (111), (200), (220) and (311) corresponded to face centered cubic crystal lattice of metallic silver. FTIR analysis revealed the involvement of various functional groups present in AED. AFM analysis confirmed the average surface roughness of synthesized AgNPs as 8.48nm. AgNPs were also screened for anticancer potential using assay of calcein AM/PI, Annexin/PI and cancer biomarkers against cancer cell line (MCF-7), while normal cell line (MCF-10A) were kept as control. Interestingly, anticancer potential was comparable to the known anticancer drug (Cisplatin), and was not detrimental to the normal cell line. Therefore, such green synthesized AgNPs may be explored as anticancer agent.

Governing factors affecting the impacts of silver nanoparticles on wastewater treatment

Silver nanoparticles (nanosilver or AgNPs) enter municipal wastewater from various sources, raising concerns about their potential adverse effects on wastewater treatment processes. We argue that the biological effects of silver nanoparticles at environmentally realistic concentrations (μgL^-1 or lower) on the performance of a full-scale municipal water resource recovery facility (WRRF) are minimal. Reactor configuration is a critical factor that reduces or even mutes the toxicity of silver nanoparticles towards wastewater microbes in a full-scale WRRF. Municipal sewage collection networks transform silver nanoparticles into silver(I)-complexes/precipitates with low ecotoxicity, and preliminary/primary treatment processes in front of biological treatment utilities partially remove silver nanoparticles to sludge. Microbial functional redundancy and microbial adaptability to silver nanoparticles also greatly alleviate the adverse effects of silver nanoparticles on the performance of a full-scale WRRF. Silver nanoparticles in a lab-scale bioreactor without a sewage collection system and/or a preliminary/primary treatment process, in contrast to being in a full scale system, may deteriorate the reactor performance at relatively high concentrations (e.g., mgL^-1 levels or higher). However, in many cases, silver nanoparticles have minimal impacts on lab-scale bioreactors, such as sequencing batch bioreactors (SBRs), especially when at relatively low concentrations (e.g., less than 1mgL^-1). The susceptibility of wastewater microbes to silver nanoparticles is species-specific. In general, silver nanoparticles have higher toxicity towards nitrifying bacteria than heterotrophic bacteria.

"Smart" nickel oxide based core-shell nanoparticles for combined chemo and photodynamic cancer therapy

We report "smart" nickel oxide nanoparticles (NOPs) as multimodal cancer therapy agent. Water-dispersible and light-sensitive NiO core was synthesized with folic acid (FA) connected bovine serum albumin (BSA) shell on entrapped doxorubicin (DOX). The entrapped drug from NOP-DOX@BSA-FA was released in a sustained way (64 hours, pH=5.5, dark conditions) while a robust release was found under red light exposure (in 1/2 hour under λmax=655 nm, 50 mW/cm(2), at pH=5.5). The cell viability, thiobarbituric acid reactive substances and diphenylisobenzofuran assays conducted under light and dark conditions revealed a high photodynamic therapy potential of our construct. Furthermore, we found that the combined effect of DOX and NOPs from NOP-DOX@BSA-FA resulted in cell death approximately eightfold high compared to free DOX. We propose that NOP-DOX@BSA-FA is a potential photodynamic therapy agent and a collective drug delivery system for the systemic administration of cancer chemotherapeutics resulting in combination therapy.

Current applications of nanoparticles in infectious diseases

For decades infections have been treated easily with drugs. However, in the 21st century, they may become lethal again owing to the development of antimicrobial resistance. Pathogens can become resistant by means of different mechanisms, such as increasing the time they spend in the intracellular environment, where drugs are unable to reach therapeutic levels. Moreover, drugs are also subject to certain problems that decrease their efficacy. This requires the use of high doses, and frequent administrations must be implemented, causing adverse side effects or toxicity. The use of nanoparticle systems can help to overcome such problems and increase drug efficacy. Accordingly, there is considerable current interest in their use as antimicrobial agents against different pathogens like bacteria, virus, fungi or parasites, multidrug-resistant strains and biofilms; as targeting vectors towards specific tissues; as vaccines and as theranostic systems. This review begins with an overview of the different types and characteristics of nanoparticles used to deliver drugs to the target, followed by a review of current research and clinical trials addressing the use of nanoparticles within the field of infectious diseases.

Antibiofilm action of a toluidine blue O-silver nanoparticle conjugate on Streptococcus mutans: a mechanism of type I photodynamic therapy

The objective of this study was to evaluate the anti-biofilm efficacy of photodynamic therapy by conjugating a photosensitizer (TBO) with silver nanoparticles (AgNP). Streptococcus mutans was exposed to laser light (630 nm) for 70 s (9.1 J cm(-2)) in the presence of a toluidine blue O-silver nanoparticle conjugate (TBO-AgNP). The results showed a reduction in the viability of bacterial cells by 4 log10. The crystal violet assay, confocal laser scanning microscopy and scanning electron microscopy revealed that the TBO-AgNP conjugates inhibited biofilm formation, increased the uptake of propidium iodide and leakage of the cellular constituents, respectively. Fluorescence spectroscopic studies confirmed the generation of OH(•) as a major reactive oxygen species, indicating type I phototoxicity. Both the conjugates down-regulated the expression of biofilm related genes compared to TBO alone. Hence TBO-AgNP conjugates were found to be more phototoxic against S. mutans biofilm than TBO alone.

Infiltration of Matrix-Non-producers Weakens the Salmonella Biofilm and Impairs Its Antimicrobial Tolerance and Pathogenicity

Bacterial biofilms display a collective lifestyle, wherein the cells secrete extracellular polymeric substances (EPS) that helps in adhesion, aggregation, stability, and to protect the bacteria from antimicrobials. We asked whether the EPS could act as a public good for the biofilm and observed that infiltration of cells that do not produce matrix components weakened the biofilm of Salmonella enterica serovar Typhimurium. EPS production was costly for the producing cells, as indicated by a significant reduction in the fitness of wild type (WT) cells during competitive planktonic growth relative to the non-producers. Infiltration frequency of non-producers in the biofilm showed a concomitant decrease in overall productivity. It was apparent in the confocal images that the non-producing cells benefit from the EPS produced by the Wild Type (WT) to stay in the biofilm. The biofilm containing non-producing cells were more significantly susceptible to sodium hypochlorite and ciprofloxacin treatment than the WT biofilm. Biofilm infiltrated with non-producers delayed the pathogenesis, as tested in a murine model. The cell types were spatially assorted, with non-producers being edged out in the biofilm. However, cellulose was found to act as a barrier to keep the non-producers away from the WT microcolony. Our results show that the infiltration of non-cooperating cell types can substantially weaken the biofilm making it vulnerable to antibacterials and delay their pathogenesis. Cellulose, a component of EPS, was shown to play a pivotal role of acting as the main public good, and to edge-out the non-producers away from the cooperating microcolony.

Effects of silver nanoparticles on neonatal testis development in mice

Background

Metal nanoparticles (MNPs) play an important role in consumer products. An increasing use of MNPs has raised concerns about potential risks for human health. Therefore, in vivo tests of MNPs are urgently required. Using mice as a model animal, the aim of the present study was designed to investigate the effect of biologically synthesized silver nanoparticles (AgNPs) on spermatogenesis in neonatal mice.

Methods

AgNPs were synthesized using Bacillus funiculus. The prepared nanoparticles were characterized using various analytical techniques such as UV–visible spectroscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, and transmission electron microscopy. The prepared AgNPs were used to investigate testis development in neonatal mice. Institute of Cancer Research neonatal male mice were used in all experiments and were treated with different doses (0, 1, and 5 mg/kg) of AgNPs five times (interval of 3 days from postnatal day [PND] 8–21) by abdominal subcutaneous injection.

Results

The results showed that the sperm abnormalities such as quality and quantity were significantly increased by the synthesized AgNPs. The diameter of the convoluted tubules shrank significantly in mice treated with AgNPs on PND28 and PND42. The results of reverse transcription-quantitative polymerase chain reaction indicated that the E1f1ay, Gsta4, and Fdx1 genes were up-regulated, and the Amh, Cx43, and Claudin-11 genes were down-regulated in response to AgNPs exposure on PND28; however, these genes recovered at PND60. AgNPs had no effect on the recombination levels of chromosomes in germ cells.

Conclusion

These results demonstrated the adverse effects of AgNPs on the male reproductive tract, particularly spermatogenesis and the quality of sperm. This study suggests that the development of nanomaterials should be safer and non-toxic to the living organisms and the potential reprotoxicity of AgNPs should be investigated more carefully.

Silver nanoparticle protein corona and toxicity: a mini-review

Silver nanoparticles are one of the most important materials in the nanotechnology industry. Additionally, the protein corona is emerging as a key entity at the nanobiointerface; thus, a comprehensive understanding of the interactions between proteins and silver nanoparticles is imperative. Therefore, literature reporting studies involving both single molecule protein coronas (i.e., bovine and human serum albumin, tubulin, ubiquitin and hyaluronic-binding protein) and complex protein coronas (i.e., fetal bovine serum and yeast extract proteins) were selected to demonstrate the effects of protein coronas on silver nanoparticle cytotoxicity and antimicrobial activity. There is evidence that distinct and differential protein components may yield a "protein corona signature" that is related to the size and/or surface curvature of the silver nanoparticles. Therefore, the formation of silver nanoparticle protein coronas together with the biological response to these coronas (i.e., oxidative stress, inflammation and cytotoxicity) as well as other cellular biophysicochemical mechanisms (i.e., endocytosis, biotransformation and biodistribution) will be important for nanomedicine and nanotoxicology. Researchers may benefit from the information contained herein to improve biotechnological applications of silver nanoparticles and to address related safety concerns. In summary, the main aim of this mini-review is to highlight the relationship between the formation of silver nanoparticle protein coronas and toxicity.

Multidimensional effects of biologically synthesized silver nanoparticles in Helicobacter pylori, Helicobacter felis, and human lung (L132) and lung carcinoma A549 cells

Silver nanoparticles (AgNPs) are prominent group of nanomaterials and are recognized for their diverse applications in various health sectors. This study aimed to synthesize the AgNPs using the leaf extract of Artemisia princeps as a bio-reductant. Furthermore, we evaluated the multidimensional effect of the biologically synthesized AgNPs in Helicobacter pylori, Helicobacter felis, and human lung (L132) and lung carcinoma (A549) cells. UV-visible (UV-vis) spectroscopy confirmed the synthesis of AgNPs. X-ray diffraction (XRD) indicated that the AgNPs are specifically indexed to a crystal structure. The results from Fourier transform infrared spectroscopy (FTIR) indicate that biomolecules are involved in the synthesis and stabilization of AgNPs. Dynamic light scattering (DLS) studies showed the average size distribution of the particle between 10 and 40 nm, and transmission electron microscopy (TEM) confirmed that the AgNPs were significantly well separated and spherical with an average size of 20 nm. AgNPs caused dose-dependent decrease in cell viability and biofilm formation and increase in reactive oxygen species (ROS) generation and DNA fragmentation in H. pylori and H. felis. Furthermore, AgNPs induced mitochondrial-mediated apoptosis in A549 cells; conversely, AgNPs had no significant effects on L132 cells. The results from this study suggest that AgNPs could cause cell-specific apoptosis in mammalian cells. Our findings demonstrate that this environmentally friendly method for the synthesis of AgNPs and that the prepared AgNPs have multidimensional effects such as anti-bacterial and anti-biofilm activity against H. pylori and H. felis and also cytotoxic effects against human cancer cells. This report describes comprehensively the effects of AgNPs on bacteria and mammalian cells. We believe that biologically synthesized AgNPs will open a new avenue towards various biotechnological and biomedical applications in the near future.

Inhalation of silver nanomaterials--seeing the risks

Demand for silver engineered nanomaterials (ENMs) is increasing rapidly in optoelectronic and in health and medical applications due to their antibacterial, thermal, electrical conductive, and other properties. The continued commercial up-scaling of ENM production and application needs to be accompanied by an understanding of the occupational health, public safety and environmental implications of these materials. There have been numerous in vitro studies and some in vivo studies of ENM toxicity but their results are frequently inconclusive. Some of the variability between studies has arisen due to a lack of consistency between experimental models, since small differences between test materials can markedly alter their behaviour. In addition, the propensity for the physicochemistry of silver ENMs to alter, sometimes quite radically, depending on the environment they encounter, can profoundly alter their bioreactivity. Consequently, it is important to accurately characterise the materials before use, at the point of exposure and at the nanomaterial-tissue, or "nanobio", interface, to be able to appreciate their environmental impact. This paper reviews current literature on the pulmonary effects of silver nanomaterials. We focus our review on describing whether, and by which mechanisms, the chemistry and structure of these materials can be linked to their bioreactivity in the respiratory system. In particular, the mechanisms by which the physicochemical properties (e.g., aggregation state, morphology and chemistry) of silver nanomaterials change in various biological milieu (i.e., relevant proteins, lipids and other molecules, and biofluids, such as lung surfactant) and affect subsequent interactions with and within cells will be discussed, in the context not only of what is measured but also of what can be visualized.

Silver polyvinyl pyrrolidone nanoparticles exhibit a capsular polysaccharide influenced bactericidal effect against Streptococcus pneumoniae

Streptococcus pneumoniae remains a leading cause of morbidity and mortality worldwide. The highly adaptive nature of S. pneumoniae exemplifies the need for next generation antimicrobials designed to avoid high level resistance. Metal based nanomaterials fit this criterion. Our study examined the antimicrobial activity of gold nanospheres, silver coated polyvinyl pyrrolidone (AgPVP), and titanium dioxide (TiO₂) against various serotypes of S. pneumoniae. Twenty nanometer spherical AgPVP demonstrated the highest level of killing among the tested materials. AgPVP (0.6 mg/mL) was able to kill pneumococcal serotypes 2, 3, 4, and 19F within 4 h of exposure. Detailed analysis of cultures during exposure to AgPVP showed that both the metal ions and the solid nanoparticles participate in the killing of the pneumococcus. The bactericidal effect of AgPVP was lessened in the absence of the pneumococcal capsular polysaccharide. Capsule negative strains, JD908 and RX1, were only susceptible to AgPVP at concentrations at least 33% higher than their respective capsule expressing counterparts. These findings suggest that mechanisms of killing used by nanomaterials are not serotype dependent and that the capsular polysaccharide participates in the inhibition. In the near future these mechanisms will be examined as targets for novel antimicrobials.

Oxidative stress mediated cytotoxicity of biologically synthesized silver nanoparticles in human lung epithelial adenocarcinoma cell line

The goal of the present study was to investigate the toxicity of biologically prepared small size of silver nanoparticles in human lung epithelial adenocarcinoma cells A549. Herein, we describe a facile method for the synthesis of silver nanoparticles by treating the supernatant from a culture of Escherichia coli with silver nitrate. The formation of silver nanoparticles was characterized using various analytical techniques. The results from UV-visible (UV-vis) spectroscopy and X-ray diffraction analysis show a characteristic strong resonance centered at 420 nm and a single crystalline nature, respectively. Fourier transform infrared spectroscopy confirmed the possible bio-molecules responsible for the reduction of silver from silver nitrate into nanoparticles. The particle size analyzer and transmission electron microscopy results suggest that silver nanoparticles are spherical in shape with an average diameter of 15 nm. The results derived from in vitro studies showed a concentration-dependent decrease in cell viability when A549 cells were exposed to silver nanoparticles. This decrease in cell viability corresponded to increased leakage of lactate dehydrogenase (LDH), increased intracellular reactive oxygen species generation (ROS), and decreased mitochondrial transmembrane potential (MTP). Furthermore, uptake and intracellular localization of silver nanoparticles were observed and were accompanied by accumulation of autophagosomes and autolysosomes in A549 cells. The results indicate that silver nanoparticles play a significant role in apoptosis. Interestingly, biologically synthesized silver nanoparticles showed more potent cytotoxicity at the concentrations tested compared to that shown by chemically synthesized silver nanoparticles. Therefore, our results demonstrated that human lung epithelial A549 cells could provide a valuable model to assess the cytotoxicity of silver nanoparticles.

Green Synthesis of Silver Nanoparticles: Structural Features and In Vivo and In Vitro Therapeutic Effects against Helicobacter pylori Induced Gastritis

This study evaluates in vivo and in vitro anti-Helicobacter pylori (H. pylori) efficacy of silver nanoparticles (Ag-NPs) prepared via a cost-effective green chemistry route wherein Peganum harmala L. seeds extract was used as a reducing and capping agent. The structural features, as elucidated by surface plasmon resonance spectrophotometry, transmission electron microscopy, and powder X-ray diffraction spectroscopy, revealed the Ag-NPs synthesized to be polydispersed in nature and spherical in shape with 5–40 nm size. A typical Ag-NPs suspension (S₅), with size being 15 nm, when tested in vitro against forty-two local isolates and two reference strains, showed a considerable anti-H. pylori activity. In case of in vivo trial against H. pylori induced gastritis, after oral administration of 16 mg/kg body weight of S₅ for seven days, a complete clearance was recorded in male albino rates. In comparative time-killing kinetics, S₅ exhibited dose- and time-dependent anti-H. pylori activity that was almost similar to tetracycline and clarithromycin, less than amoxicillin, but higher than metronidazole. Furthermore, S₅ was found to be an equally effective anti-H. pylori agent at low (≤4) and high pH with no drug resistance observed even up to 10 repeated exposures while a significant drug resistance was recorded for most of the standard drugs employed. The present results revealed the potential of the synthesized Ag-NPs as safer bactericidal agents for the treatment of H. pylori induced gastritis.

Synergy of silver nanoparticles and aztreonam against Pseudomonas aeruginosa PAO1 biofilms

Pathogenic bacterial biofilms, such as those found in the lungs of patients with cystic fibrosis (CF), exhibit increased antimicrobial resistance, due in part to the inherent architecture of the biofilm community. The protection provided by the biofilm limits antimicrobial dispersion and penetration and reduces the efficacy of antibiotics that normally inhibit planktonic cell growth. Thus, alternative antimicrobial strategies are required to combat persistent infections. The antimicrobial properties of silver have been known for decades, but silver and silver-containing compounds have recently seen renewed interest as antimicrobial agents for treating bacterial infections. The goal of this study was to assess the efficacy of citrate-capped silver nanoparticles (AgNPs) of various sizes, alone and in combination with the monobactam antibiotic aztreonam, to inhibit Pseudomonas aeruginosa PAO1 biofilms. Among the different sizes of AgNPs examined, 10-nm nanoparticles were most effective in inhibiting the recovery of P. aeruginosa biofilm cultures and showed synergy of inhibition when combined with sub-MIC levels of aztreonam. Visualization of biofilms treated with combinations of 10-nm AgNPs and aztreonam indicated that the synergistic bactericidal effects are likely caused by better penetration of the small AgNPs into the biofilm matrix, which enhances the deleterious effects of aztreonam against the cell envelope of P. aeruginosa within the biofilms. These data suggest that small AgNPs synergistically enhance the antimicrobial effects of aztreonam against P. aeruginosa in vitro, and they reveal a potential role for combinations of small AgNPs and antibiotics in treating patients with chronic infections.