Bactericidal activity of Ag-zeolite mediated by reactive oxygen species under aerated conditions

Effect of Zeolite Incorporation on the Ion Release Properties of Silver-Reinforced Glass Ionomer Cement

BACKGROUND

Zeolite can release antimicrobial silver ions in a targeted and controlled manner for an extended time, selectively inhibiting the growth of pathogenic oral bacteria when added to dental materials. The objective of this study was to investigate the effect of the addition of zeolite to silver-reinforced glass ionomer cement on the release of silver ions over time.

METHODS

Five concentrations of silver-zeolite (0%, 0.5%, 1%, 2%, 4% wt) were incorporated into silver-reinforced GIC in the form of 10 mm × 2 mm circular disks (n = 5). The disks were incubated in deionized water at 37 °C and ion release from the samples was measured at 1, 2, 7, and 30 days after immersion by inductively coupled atomic emission spectroscopy.

RESULTS

Incorporating silver-zeolite increased silver ion release from silver-reinforced GIC disks compared to the control disks (p < 0.05), while incorporating zeolite alone had no effect. Higher concentrations of added silver-zeolite resulted in increased silver ion release. Sustained silver ion release was observed for up to 30 days.

CONCLUSION

Adding silver-zeolite to silver-reinforced GIC may enhance its extended antibacterial effect in the oral cavity.

Zeolite Properties, Methods of Synthesis, and Selected Applications

Zeolites, a group of minerals with unique properties, have been known for more than 250 years. However, it was the development of methods for hydrothermal synthesis of zeolites and their large-scale industrial applications (oil processing, agriculture, production of detergents and building materials, water treatment processes, etc.) that made them one of the most important materials of the 20th century, with great practical and research significance. The orderly, homogeneous crystalline and porous structure of zeolites, their susceptibility to various modifications, and their useful physicochemical properties contribute to the continuous expansion of their practical applications in both large-volume processes (ion exchange, adsorption, separation of mixture components, catalysis) and specialized ones (sensors). The following review of the knowledge available in the literature on zeolites aims to present the most important information on the properties, synthesis methods, and selected applications of this group of aluminosilicates. Special attention is given to the use of zeolites in agriculture and environmental protection.

Antimicrobial and Virus Adsorption Properties of Y-Zeolite Exchanged with Silver and Zinc Cations

The antimicrobial activity of silver and zinc exchanged cations in Y-zeolite (Ag/CBV-600, Zn/CBV-600) is evaluated against Staphylococcus aureus (gram (+)) and Escherichia coli (gram (-)) bacteria along with their adsorption capacity for viruses: brome mosaic virus (BMV), cowpea chlorotic mottle virus (CCMV), and the bacteriophage MS2. The physicochemical properties of synthesized nanomaterials are characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). According to the obtained results, the main species associated with the exchanged ions are Ag+ and Zn2+ cations with the concentration of around 1 atomic %. The incorporation of cations does not modify the Y-zeolite framework. The Ag/CBV-600 and Zn/CBV-600 materials show an inactivation of 90% for both gram (+) and gram (-) bacteria at 16 h at a relatively low concentration of nanomaterial (0.5 mg/mL). Moreover, the samples present good adsorption capacity for BMV, CCMV, and MS2 viruses showing adsorption higher than 40% after 2 h of interaction with the viruses. These prominent results allow the further usage of nanomaterials as an effective remedy to inhibit and reduce the spread of viruses such as SARS-CoV-2 or other gram (+) or gram (-) bacteria.

Universal Single-Step Approach to the Immobilization of Cyclodextrins in a Supercritical Medium for Capturing Drug, Dye, and Metal Nanoclusters

By utilizing nanoreactor-like structures, the immobilization of macromolecules such as calixarenes and cyclodextrins (CD) with bucket-like structures provides new possibilities for engineered surface-molecule systems. The practical use of any molecular system depends on the availability of a universal procedure for immobilizing molecules with torus-like structures on various surfaces while maintaining identical operating parameters. There are currently several steps, including toxic solvent-based approaches using modified β-CD to covalently attach to surfaces with multistep reactions. However, the existing multistep process results in molecular orientation, restricts the accessibility of the hydrophobic barrel of β-CD's for practical use, and is effectively unable to use the surfaces immobilized with β-CD for a variety of applications. In this study, it was demonstrated that β-CD attached to the oxide-based semiconductor and metal surfaces through a condensation reaction between the hydroxyl-terminated oxide-based semiconductor/metal oxide and β-CD in supercritical carbon dioxide (SCCO₂) as a medium. The primary benefit of SCCO₂-assisted grafting of unmodified β-CD on various oxide-based metal and semiconductor surfaces is that it is a simple, efficient, one-step process and that it is ligand-free, scalable, substrate-independent, and uses minimal energy. Various physical microscopy and chemical spectroscopic methods were used to analyze the grafted β-CD oligomers. The application of the grafted β-CD films was demonstrated by the immobilization of rhodamine B (RhB), a dye, and dopamine, a drug. The in situ nucleation and growth of silver nanoclusters (AgNCs) in the molecular systems were studied for antibacterial and tribological properties by utilizing the guest-host interaction ability of β-CD.

Versatile Silver-Nanoparticle-Impregnated Membranes for Water Treatment: A Review

Increased affordability, smaller footprint, and high permeability quality that meets stringent water quality standards have accelerated the uptake of membranes in water treatment. Moreover, low pressure, gravity-based microfiltration (MF) and ultrafiltration (UF) membranes eliminate the use of electricity and pumps. However, MF and UF processes remove contaminants by size exclusion, based on membrane pore size. This limits their application in the removal of smaller matter or even harmful microorganisms. There is a need to enhance the membrane properties to meet needs such as adequate disinfection, flux amelioration, and reduced membrane fouling. To achieve these, the incorporation of nanoparticles with unique properties in membranes has potential. Herein, we review recent developments in the impregnation of polymeric and ceramic microfiltration and ultrafiltration membranes with silver nanoparticles that are applied in water treatment. We critically evaluated the potential of these membranes in enhanced antifouling, increased permeability quality and flux compared to uncoated membranes. Despite the intensive research in this area, most studies have been performed at laboratory scale for short periods of time. There is a need for studies that assess the long-term stability of the nanoparticles and the impact on disinfection and antifouling performance. These challenges are addressed in this study and future directions.

MIL-101 (Fe) @Ag Rapid Synergistic Antimicrobial and Biosafety Evaluation of Nanomaterials

Metal-organic frameworks (MOFs), which have become popular in recent years as excellent carriers of drugs and biomimetic materials, have provided new research ideas for fighting pathogenic bacterial infections. Although various antimicrobial metal ions can be added to MOFs with physical methods, such as impregnation, to inhibit bacterial multiplication, this is inefficient and has many problems, such as an uneven distribution of antimicrobial ions in the MOF and the need for the simultaneous addition of large doses of metal ions. Here, we report on the use of MIL-101(Fe)@Ag with efficient metal-ion release and strong antimicrobial efficiency for co-sterilization. Fe-based MIL-101(Fe) was synthesized, and then Ag+ was uniformly introduced into the MOF by the substitution of Ag+ for Fe3+. Scanning electron microscopy, powder X-ray diffraction (PXRD) Fourier transform infrared spectroscopy, and thermogravimetric analysis were used to investigate the synthesized MIL-101(Fe)@Ag. The characteristic peaks of MIL-101(Fe) and silver ions could be clearly seen in the PXRD pattern. Comparing the diffraction peaks of the simulated PXRD patterns clearly showed that MIL-101(Fe) was successfully constructed and silver ions were successfully loaded into MIL-101(Fe) to synthesize an MOF with a bimetallic structure, that is, the target product MIL-101(Fe)@Ag. The antibacterial mechanism of the MOF material was also investigated. MIL-101(Fe)@Ag exhibited low cytotoxicity, so it has potential applications in the biological field. Overall, MIL-101(Fe)@Ag is an easily fabricated structurally engineered nanocomposite with broad-spectrum bactericidal activity.

Applications of green technologies‐based approaches for food safety enhancement: A comprehensive review

Food is the basic necessity for life that always motivated man for its preservation and making it available for an extended period. Food scientists always tried to preserve it with minimum deterioration in quality by employing and investigating innovative preservation techniques. The food sector always remained in search of eco‐friendly and sustainable solutions to tackle food safety challenges. Green technologies (ozone, pulsed electric field, ohmic heating, photosensitization, ultraviolet radiations, high‐pressure processing, ultrasonic, nanotechnology) are in high demand owing to their eco‐friendly, rapid, efficient, and effective nature in controlling microbes with a negligible residual impact on food quality during processing. The use of green technologies would be a desirable substitute for conventionally available preservation techniques. This paper discusses different food preservation techniques with special reference to green technologies to minimize the deleterious impact on the environment and employs these innovative technologies to play role in enhancing the food safety.

A review on removal strategies of microorganisms from water environment using nanomaterials and their behavioural characteristics

Significant findings for microbial removal have led to expertise on several kinds of nanomaterials that made new paths for removing various biological contaminants in a variety of water resources in recent years. Furthermore, advancements in multifunctional nanocomposites synthesis pave the enhanced possibility for their use in water treatment system design. The adsorption towards microbial elimination has been reviewed and compared in this review article using four common kinds of nanomaterials: carbon materials, metal oxides, metal/metal oxides, polymeric metal oxide nanocomposites and their most important mechanistic behavior also discussed. We also describe and analyze recent findings on the effects of engineered nanomaterials on microbial communities in natural and artificial environments. Understanding the removal mechanistic strategy is crucial to improving the nanoparticles (NPs) efficiency and increasing their applicability against a variety of bacteria in various environmental conditions. Also, our study focused on their behavioral effects on microbial structure and functionality towards the removal. Future research opportunities connected to the use of nanomaterials in microbial control and inactivation with societal and health implications are also discussed. We also highlight a number of interesting research subjects that might be of futuristic interest to the scientific community.

Long term antifungal efficacy of silver-zinc zeolite nanoparticles incorporated in two soft denture liners - An in vitro assessment

Background

There is generally a lack of compliance in patients who report with oral candidiasis, as they are advised to temporarily stop wearing the prosthesis and are prescribed topical antifungals which are generally unpleasant to taste and follow a rigorous schedule. Furthermore, with the alarming evidence of drug resistance, there is a need for an enhanced drug and drug delivery system. The aim of the study was to determine the dose-dependent antifungal efficacy of silver-zinc zeolite nanoparticles (SZZ-NPs) when incorporated in two brands of soft denture liners against Candida albicans.

Materials and Methods

A total of 72 samples were made to determine the in vitro antifungal efficacy of SZZ-NPs and fluconazole by measuring the mean inhibition diameter (MID). Two concentrations of SZZ-NPs were compared (0.5%, 2% w/w) with fluconazole 5%w/w which is routinely prescribed. The antifungals were incorporated in two types of commercially available soft denture liners (Visco gel, GC soft denture liner). The MIDs were measured at day 1, day 7, day 15, and day 30. The values obtained (P < 0.001) were analyzed with one-way ANOVA, Tukey's post hoc, and independent t-test.

Results

A statistically significant difference (P < 0.001) was noted among all the antifungal agents at all the time intervals tested. The anti-fungal efficacy of SSZ-NPs 2% w/w incorporated in GC soft denture liner was significantly superior (P < 0.001) to all groups tested and it retained its antifungal efficacy even on day 30 (MID: 18.33 ± 2.44).

Conclusion

SZZ-NPs 0.5%w/w, 2%w/w, and fluconazole 5%w/w can be incorporated with soft denture liners against C. albicans. Fluconazole 5%w/w is the recommended choice for short-term antifungal efficacy, while SZZ-NPs 2%w/w is recommended when long-term antifungal efficacy is needed. GC soft denture liner was the recommended choice.

Preparation and characterization of glucose-conjugated super-paramagnetic iron oxide nanoparticles (G-SPIONs) for removal of Edwardsiella tarda and Aeromonas hydrophila from water

The present research was conducted to prepare efficient G-SPIONs by co-precipitation to remove Edwardsiella tarda and Aeromonas hydrophila from the aqueous solution. The synthesized G-SPIONs were characterized by UV-Vis spectrophotometer, DLS, FEG-TEM, FT-IR, XRD, and VSM analysis. The results showed that the synthesized G-SPIONs had super-paramagnetic properties (58.31 emu/g) and spherical shape (16 ± 3 nm). The antibacterial activity was assessed in sterilized distilled water at different G-SPIONs concentrations viz. 0, 1.5, 3, 6, 12, 24, 48, 120, and 240 mg/L against E. tarda and A. hydrophila with various bacterial loads viz. 1 × 10³ , 1 × 10⁴ , 1 × 10⁵ , 1 × 10⁶ , and 1 × 10⁷  CFU/ml at different time intervals 15, 30, 45, and 60 min. At a lower bacterial load of E. tarda and A. hydrophila 1 × 10³ -1 × 10⁴  CFU/ml, 100% bacterial load was removed by 15 min exposure with NPs concentration 6-48 mg/L and 1.5-6 mg/L, respectively. Cent percent bacterial removal was observed in both the bacterial species even at higher bacterial load (1 × 10⁵ -1 × 10⁷  CFU/ml) by increasing exposure time (15-60 min) and nanoparticle concentration as well (24-240 mg/L). At an initial bacterial load of E. tarda and A. hydrophila (1 × 10³ -1 × 10⁷  CFU/ml), the EC₅₀ ranged between 0.01-6.51 mg/L and 0.02-3.84 mg/L, respectively, after 15-60 min exposure. Thus, it is concluded that the antibacterial effect of G-SPIONs depends on concentration and exposure time. Hence, G-SPIONs can be used as an antibacterial/biocidal agent to treat Edwardsiellosis and Aeromonosis disease in aquaculture.

Antimicrobial carbon-dot–stabilized silver nanoparticles

Carbon-dot–stabilized silver nanoparticles (CD–AgNPs) with high stability and low toxicity exhibit good antibacterial activity and broad-spectrum performance.

Selective strategies for antibacterial regulation of nanomaterials

Recalcitrant bacterial infection, as a worldwide challenge, causes large problems for human health and is attracting great attention. The excessive antibiotic-dependent treatment of infections is prone to induce antibiotic resistance. A variety of unique nanomaterials provide an excellent toolkit for killing bacteria and preventing drug resistance. It is of great importance to summarize the design rules of nanomaterials for inhibiting the growth of pathogenic bacteria. We completed a review involving the strategies for regulating antibacterial nanomaterials. First, we discuss the antibacterial manipulation of nanomaterials, including the interaction between the nanomaterial and the bacteria, the damage of the bacterial structure, and the inactivation of biomolecules. Next, we identify six main factors for controlling the antibacterial activity of nanomaterials, including their element composition, size dimensions, surface charge, surface topography, shape selection and modification density. Every factor possesses a preferable standard for maximizing antibacterial activity, providing universal rules for antibacterial regulation of nanomaterials. We hope this comprehensive review will help researchers to precisely design and synthesize nanomaterials, developing intelligent antibacterial agents to address bacterial infections.

This review builds universal design rules for the antibacterial regulation of nanomaterials.

Preparation and Antimicrobial Activity of Antibacterial Silver-Loaded Polyphosphazene Microspheres

Poly(cyclotriphosphazene-co-4,4'-diaminodiphenyl ether) (PPO) microspheres were prepared via a precipitation polymerization method, using hexachlorocyclotriphosphazene (HCCP) and 4,4'-diaminodiphenyl ether (ODA) as monomers. Silver-loaded PPO (PPOA) microspheres were generated by the in situ loading of silver nanoparticles onto the surface by Ag⁺ reduction. Our results showed that PPOA microspheres were successfully prepared with a relatively uniform distribution of silver nanoparticles on microsphere surfaces. PPOA microspheres had good thermal stability and excellent antibacterial activity towards Escherichia coli and Staphylococcus aureus. Furthermore, PPOA microspheres exhibited lower cytotoxicity when compared to citrate-modified silver nanoparticles (c-Ag), and good sustained release properties. Our data indicated that polyphosphazene-based PPOA microspheres are promising antibacterial agents in the biological materials field.

Microbial mortality behavior promoted by silver (Ag+/Ago)-modified zeolite-rich tuffs for water disinfection

BACKGROUND

In developing countries, death due to diseases caused by fecal-oral ingestion can be avoided by taking action on drinking water issues. Adequate access to water treatment systems to reduce infections is a critical cause. Silver has been used as an antibacterial product, including biomedical applications. Therefore, in this paper, the effect of the chemical speciation of silver from silver-modified zeolite-rich tuffs on the mortality of Escherichia coli (E. coli), Streptococcus faecalis (S. faecalis) and Candida albicans (C. albicans) suspended in aqueous solution was investigated for disinfection purposes.

METHODS

The following aspects were considered to develop the investigation: a) the technique to prepare the modified zeolitic materials, either with ionic silver or silver nanoparticles, which were obtained in two ways: one, with grapefruit extract and the second, by using non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates; b) the response of the prokaryotes (bacteria) and eukaryote (yeast) microorganisms to disinfectant agents in batch systems; c) the disinfection processes as a function of time to obtain kinetics parameters; and d) the kinetics of the silver release from the silver-modified zeolite-rich tuffs, considering the models of Higuchi and Korsmeyer. The zeolitic materials were characterized by low-vacuum scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

RESULTS

The non-thermal plasma reduced ionic silver is more efficient at generating silver compounds with several oxidation states, which are essential during the microbial inhibition process. For the bacterial (E. coli and S. faecalis), the materials with nanoparticles were efficient to inactivate them. However, the yeast (C. albicans) reaches the total inactivation when the zeolitic material contains ionic silver in the crystalline network.

CONCLUSION

The E. coli, S. faecalis and C. albicans survival behavior suspended in aqueous solutions after contact with Ag-modified natural zeolites depends on the chemical speciation of the silver present in these materials, Ag⁺¹ in the case of OAg_iZ or nanoparticles of Ag^o promoted by the grapefruit extract (OAg_npTZ), as well as by non-thermal plasma generated in a dielectric barrier discharge reactor of parallel plates (OAg_npPZ). In general, the concentration of silver in the aqueous solution after the disinfection process cannot exceed the recommended levels established for international organizations. The OAg_npPZ is a potential microbicide agent against E. coli and C. albicans, and the OAg_{n pT}Z for F. faecalis.Graphical abstractARTWORK.

Pollution, Toxicity and Carcinogenicity of Organic Dyes and their Catalytic Bio-Remediation

Water pollution due to waste effluents of the textile industry is seriously causing various health problems in humans. Water pollution with pathogenic bacteria, especially Escherichia coli (E. coli) and other microbes is due to the mixing of fecal material with drinking water, industrial and domestic sewage, pasture and agricultural runoff. Among the chemical pollutants, organic dyes due to toxic nature, are one of the major contaminants of industrial wastewater. Adequate sanitation services and drinking quality water would eliminate 200 million cases of diarrhea, which results in 2.1 million less deaths caused by diarrheal disease due to E. coli each year. Nanotechnology is an excellent platform as compared to conventional treatment methods of water treatment and remediation from microorganisms and organic dyes. In the current study, toxicity and carcinogenicity of the organic dyes have been studied as well as the remediation/inactivation of dyes and microorganism has been discussed. Remediation by biological, physical and chemical methods has been reviewed critically. A physical process like adsorption is cost-effective, but can't degrade dyes. Biological methods were considered to be ecofriendly and cost-effective. Microbiological degradation of dyes is cost-effective, eco-friendly and alternative to the chemical reduction. Besides, certain enzymes especially horseradish peroxidase are used as versatile catalysts in a number of industrial processes. Moreover, this document has been prepared by gathering recent research works related to the dyes and microbial pollution elimination from water sources by using heterogeneous photocatalysts, metal nanoparticles catalysts, metal oxides and enzymes.

New insight into fates of sulfonamide and tetracycline resistance genes and resistant bacteria during anaerobic digestion of manure at thermophilic and mesophilic temperatures

This study investigated the variations in antibiotic (sulfonamide and tetracycline) resistance genes (ARGs) and resistant bacteria (ARB) during manure anaerobic digestion (AD) at 35 ℃ and 55 ℃, and discussed the mechanisms of variations in ARGs. The AD lasted for 60 days, five ARGs and intI1 each decreased in abundance after AD at the thermophilic temperature, while only half decreased at the mesophilic temperature. On days 10, 30, and 60, sulfonamide and tetracycline ARB were screened on selective media. During thermophilic AD, ARB numbers reduced by 4-log CFUs per gram dry manure, but only by approximately 1-log CFU at the mesophilic temperature. However, ARB composition analysis showed that at either temperature, no significant reduction in identified ARB species was observed. Furthermore, 72 ARB clones were randomly selected to detect the ARGs they harbored, and the results showed that each ARG was harbored by various hosts, and no definitive link existed between ARGs and bacterial species. In addition, by comparison with the identified host by culture method, the host prediction results based on the correlation analysis between ARGs and the bacterial community was proven to be unreliable. Overall, these findings indicated that relationships between ARB and ARGs were intricate.

Nanotechnologies in Food Science: Applications, Recent Trends, and Future Perspectives

Nanotechnology is a key advanced technology enabling contribution, development, and sustainable impact on food, medicine, and agriculture sectors. Nanomaterials have potential to lead qualitative and quantitative production of healthier, safer, and high-quality functional foods which are perishable or semi-perishable in nature. Nanotechnologies are superior than conventional food processing technologies with increased shelf life of food products, preventing contamination, and production of enhanced food quality. This comprehensive review on nanotechnologies for functional food development describes the current trends and future perspectives of advanced nanomaterials in food sector considering processing, packaging, security, and storage. Applications of nanotechnologies enhance the food bioavailability, taste, texture, and consistency, achieved through modification of particle size, possible cluster formation, and surface charge of food nanomaterials. In addition, the nanodelivery-mediated nutraceuticals, synergistic action of nanomaterials in food protection, and the application of nanosensors in smart food packaging for monitoring the quality of the stored foods and the common methods employed for assessing the impact of nanomaterials in biological systems are also discussed.

Antimicrobial Properties of Encapsulated Antimicrobial Natural Plant Products for Ready-to-Eat Carrots

The antimicrobial activity of natural antimicrobials (fruit extracts, essential oils and derivates), was assessed against six bacteria species (E. coli O157:H7, L. monocytogenes, S. Typhimurium, B. subtilis, E. faecium and S. aureus), two molds (A. flavus and P. chrysogenum) and a yeast (C. albicans) using disk diffusion method. Then, the antimicrobial compounds having high inhibitory capacity were evaluated for the determination of their minimum inhibitory, bactericidal and fungicidal concentration (MIC, MBC and MFC respectively). Total phenols and flavonoids content, radical scavenging activity and ferric reducing antioxidant power of selected compounds were also evaluated. Based on in vitro assays, five antimicrobial compounds were selected for their lowest effective concentration. Results showed that, most of these antimicrobial compounds had a high concentration of total phenols and flavonoids and a good anti-oxidant and anti-radical activity. In situ study showed that natural antimicrobials mix, applied on the carrot surface, reduced significantly the count of the initial mesophilic total flora (TMF), molds and yeasts and allowed an extension of the shelf-life of carrots by two days as compared to the control. However, the chemical treatment (mix of peroxyacetic acid and hydrogen peroxide) showed antifungal activity and a slight reduction of TMF.

P. Oliveira R, Stoševski I, Krstić J, Hercigonja R, Miljanić Š, Santos DMF, Šljukić B. Evaluation of silver-incorporating zeolites as bifunctional electrocatalysts for direct borohydride fuel cells

Low cost zeolites with incorporated silver show high activity for both oxygen reduction and borohydride oxidation reaction.

Selective proteolysis by matrix metalloproteinases of photo-oxidised dermal extracellular matrix proteins

Photodamage in chronically sun-exposed skin manifests clinically as deep wrinkles and histologically as extensive remodelling of the dermal extracellular matrix (ECM) and in particular, the elastic fibre system. We have shown previously that loss of fibrillin microfibrils, a key elastic fibre component, is a hallmark of early photodamage and that these ECM assemblies are susceptible in vitro to physiologically attainable doses of ultraviolet radiation (UVR). Here, we test the hypotheses that UVR-mediated photo-oxidation is the primary driver of fibrillin microfibril and fibronectin degradation and that prior UVR exposure will enhance the subsequent proteolytic activity of UVR-upregulated matrix metalloproteinases (MMPs). We confirmed that UVB (280-315 nm) irradiation in vitro induced structural changes to both fibrillin microfibrils and fibronectin and these changes were largely reactive oxygen species (ROS)-driven, with increased ROS lifetime (D₂O) enhancing protein damage and depleted O₂ conditions abrogating it. Furthermore, we show that although exposure to UVR alone increased microfibril structural heterogeneity, exposure to purified MMPs (1, -3, -7 and - 9) alone had minimal effect on microfibril bead-to-bead periodicity; however, microfibril suspensions exposed to UVR and then MMPs were more structurally homogenous. In contrast, the susceptibly of fibronectin to proteases was unaffected by prior UVR exposure. These observations suggest that both direct photon absorption and indirect production of ROS are important mediators of ECM remodelling in photodamage. We also show that fibrillin microfibrils are relatively resistant to proteolysis by MMPs -1, -3, -7 and - 9 but that these MMPs may selectively remove damaged microfibril assemblies. These latter observations have implications for predicting the mechanisms of tissue remodelling and targeted repair.

Advances in concrete materials for sewer systems affected by microbial induced concrete corrosion: A review

Microbial induced concrete corrosion (MICC) is recognized as one of the main degradation mechanisms of subsurface infrastructure worldwide, raising the demand for sustainable construction materials in corrosive environments. This review aims to summarize the key research progress acquired during the last decade regarding the understanding of MICC reaction mechanisms and the development of durable materials from an interdisciplinary perspective. Special focus was laid on aspects governing concrete - micoorganisms interaction since being the central process steering biogenic acid corrosion. The insufficient knowledge regarding the latter is proposed as a central reason for insufficient progress in tailored material development for aggressive wastewater systems. To date no cement-based material exists, suitable to withstand the aggressive conditions related to MICC over its entire service life. Research is in particular needed on the impact of physiochemical material parameters on microbial community structure, growth characteristics and limitations within individual concrete speciation. Herein an interdisciplinary approach is presented by combining results from material sciences, microbiology, mineralogy and hydrochemistry to stimulate the development of novel and sustainable materials and mitigation strategies for MICC. For instance, the application of antibacteriostatic agents is introduced as an effective instrument to limit microbial growth on concrete surfaces in aggressive sewer environments. Additionally, geopolymer concretes are introduced as highly resistent in acid environments, thus representing a possible green alternative to conventional cement-based construction materials.

The Detailed Bactericidal Process of Ferric Oxide Nanoparticles on E. coli

While nanoparticles exert bactericidal effects through the generation of reactive oxygen species (ROS), the processes of the internalization of and the direct physical damage caused by iron oxide nanoparticles are not completely clear. We hypothesize that direct physical or mechanical damage of the cell membrane and cytoplasmic integrity by nanoparticles is another major cause of bacterial death besides ROS. The aim of this study is to investigate the process of the internalization of iron oxide nanoparticles, and to evaluate the effect of direct physical or mechanical damage on bacterial cell growth and death. The results demonstrate that iron oxide nanoparticles not only inhibited E. coli cell growth, but also caused bacterial cell death. Iron oxide nanoparticles produced significantly elevated ROS levels in bacteria. Transmission electronic microscopy demonstrated that iron oxide nanoparticles were internalized into and condensed the cytoplasm. Strikingly, we observed that the internalized nanoparticles caused intracellular vacuole formation, instead of simply adsorbing thereon; and formed clusters on the bacterial surface and tore up the outer cell membrane to release cytoplasm. This is the first time that the exact process of the internalization of iron oxide nanoparticles has been observed. We speculate that the intracellular vacuole formation and direct physical or mechanical damage caused by the iron oxide nanoparticles caused the bactericidal effect, along with the effects of ROS.

Essential oils and metal ions as alternative antimicrobial agents: a focus on tea tree oil and silver

The increasing occurrence of hospital-acquired infections and the emerging problems posed by antibiotic-resistant microbial strains have both contributed to the escalating cost of treatment. The presence of infection at the wound site can potentially stall the healing process at the inflammatory stage, leading to the development of a chronic wound. Traditional wound treatment regimes can no longer cope with the complications posed by antibiotic-resistant strains; hence, there is a need to explore the use of alternative antimicrobial agents. Pre-antibiotic compounds, including heavy metal ions and essential oils, have been re-investigated for their potential use as effective antimicrobial agents. Essential oils have potent antimicrobial, antifungal, antiviral, anti-inflammatory, antioxidant and other beneficial therapeutic properties. Similarly, heavy metal ions have also been used as disinfecting agents because of their broad spectrum activities. Both of these alternative antimicrobials interact with many different intracellular components, thereby resulting in the disruption of vital cell functions and eventually cell death. This review will discuss the application of essential oils and heavy metal ions, particularly tea tree oil and silver ions, as alternative antimicrobial agents for the treatment of chronic, infected wounds.

Study of photodynamic activity of Au@SiO2 core-shell nanoparticles in vitro

Metal-semiconductor core-shell type Au@SiO2 nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, HR-TEM and EDAX techniques. The resulting modified core-shell nanoparticles shows that the formation of singlet oxygen, which was confirmed by ESR technique. The photohemolysis studies were carried out under two different experimental conditions. It is observed that the photohemolysis increases with concentration as well as light dose. Cell viability of the core-shell nanoparticles against HeLa cell lines were studied by MTT assay method. The outcomes of the present study indicate that, the Au@SiO2 core-shell nanoparticles are extremely stable with a very high photodynamic efficiency under visible light illumination.

Antimicrobial activity of silver loaded MnO2 nanomaterials with different crystal phases against Escherichia coli

Silver-loaded MnO2 nanomaterials (Ag/MnO2), including Ag/α-MnO2, Ag/β-MnO2, Ag/γ-MnO2 and Ag/δ-MnO2 nanorods, were prepared with hydrothermal and impregnation methods. The bactericidal activities of four types of Ag/MnO2 nanomaterials against Escherichia coli were investigated and an inactivation mechanism involving Ag(+) and reactive oxygen species (ROS) was also proposed. The bactericidal activities of Ag/MnO2 depended on the MnO2 crystal phase. Among these nanomaterials, Ag/β-MnO2 showed the highest bactericidal activity. There was a 6-log decrease in E. coli survival number after treatment with Ag/β-MnO2 for 120min. The results of 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping measurements by electron spin resonance indicate OH and O2‾ formation with addition of Ag/β-MnO2, Ag/γ-MnO2 or Ag/δ-MnO2. The strongest peak of OH appeared for Ag/β-MnO2, while no OH or O2‾ signal was found over Ag/α-MnO2. Through analysis of electron spin resonance (ESR) and Ag(+) elution results, it could be deduced that the toxicity of Ag(+) eluted from Ag/MnO2 nanomaterials and ROS played the main roles during the bactericidal process. Silver showed the highest dispersion on the surface of β-MnO2, which promoted ROS formation and the increase of bactericidal activity. Experimental results also indicated that Ag/MnO2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane.

Escherichia coli under Ionic Silver Stress: An Integrative Approach to Explore Transcriptional, Physiological and Biochemical Responses

For a better understanding of the systemic effect of sub-lethal micromolar concentrations of ionic silver on Escherichia coli, we performed a multi-level characterization of cells under Ag⁺-mediated stress using an integrative biology approach combining physiological, biochemical and transcriptomic data. Physiological parameters, namely bacterial growth and survival after Ag⁺ exposure, were first quantified and related to the accumulation of intracellular silver, probed for the first time by nano secondary ion mass spectroscopy at sub-micrometer lateral resolution. Modifications in E. coli biochemical composition were evaluated under Ag⁺-mediated stress by in situ synchrotron Fourier-transform infrared microspectroscopy and a comprehensive transcriptome response was also determined. Using multivariate statistics, correlations between the physiological parameters, the extracellular concentration of AgNO₃ and the intracellular silver content, gene expression profiles and micro-spectroscopic data were investigated. We identified Ag⁺-dependent regulation of gene expression required for growth (e.g. transporter genes, transcriptional regulators, ribosomal proteins), for ionic silver transport and detoxification (e.g. copA, cueO, mgtA, nhaR) and for coping with various types of stress (dnaK, pspA, metA,R, oxidoreductase genes). The silver-induced shortening of the acyl chain of fatty acids, mostly encountered in cell membrane, was highlighted by microspectroscopy and correlated with the down-regulated expression of genes involved in fatty acid transport (fadL) and synthesis/modification of lipid A (lpxA and arnA). The increase in the disordered secondary structure of proteins in the presence of Ag⁺ was assessed through the conformational shift shown for amides I and II, and further correlated with the up-regulated expression of peptidase (hfq) and chaperone (dnaJ), and regulation of transpeptidase expression (ycfS and ycbB). Interestingly, as these transpeptidases act on the structural integrity of the cell wall, regulation of their expression may explain the morphological damage reported under Ag⁺-mediated stress. This result clearly demonstrates that the cell membrane is a key target of ionic silver.

Dynamic Mechanisms of the Bactericidal Action of an Al2O3-TiO2-Ag Granular Material on an Escherichia coli Strain

The bactericidal activity of an Al2O3-TiO2-Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al2O3-TiO2-Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (10(5) genomic units·ml(-1)) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced.

A multi-parametric approach assessing microbial viability and organic matter characteristics during managed aquifer recharge

Soil column (SC) experiments were conducted to investigate the feasibility of using silver nanoparticles (AgNPs) as microbial inhibitors; the microbial viability affecting the degradation of pharmaceutically active compounds (PhACs) and the characteristics of organic matter during managed aquifer recharge were specifically evaluated. Natural surface water samples treated with AgNPs (0, 2.5, 5, and 10 mg L(-1)) were continually fed into the soil columns for 2 years. The adverse impact of AgNPs on the cell membrane integrity and microbial enzymatic activity was quantitatively determined using flow cytometry and adenosine triphosphate analysis. The increase in AgNP concentration in the feed water (up to 10 mg L(-1)) resulted in a corresponding deterioration in the performance of the managed aquifer recharge (MAR), with respect to the removal of organic carbon, oxidation of nitrogenous compounds, and PhAC attenuation. The fluorescence excitation-emission matrices of feed water and treated water showed the favorable removal of protein-like substances compared to humic-like substances regardless of the AgNP concentrations; however, the extent of removed fractions decreased noticeably when the microbial viability was lowered via AgNP treatment. The biological oxidation of organic nitrogen was almost completely inhibited when 10 mg L(-1) AgNP was added during soil passage. The attenuation of bezafibrate, ketoprofen, diclofenac, clofibric acid, and gemfibrozil was strongly associated with the significant deterioration in biodegradation as a result of AgNP activity.

DNA/Ag Nanoparticles as Antibacterial Agents against Gram-Negative Bacteria

Silver (Ag) nanoparticles were produced using DNA extracted from salmon milt as templates. Particles spherical in shape with an average diameter smaller than 10 nm were obtained. The nanoparticles consisted of Ag as the core with an outermost thin layer of DNA. The DNA/Ag hybrid nanoparticles were immobilized over the surface of cotton based fabrics and their antibacterial efficiency was evaluated using E. coli as the typical Gram-negative bacteria. The antibacterial experiments were performed according to the Antibacterial Standard of Japanese Association for the Functional Evaluation of Textiles. The fabrics modified with DNA/Ag nanoparticles showed a high enough inhibitory and killing efficiency against E. coli at a concentration of Ag ≥ 10 ppm.

Preparation and assessment of antimicrobial properties of bimetallic materials based on NaY zeolite

ZnAg–Y was the most active material tested against the bacteria Escherichia coli and the yeast Saccharomyces cerevisiae as indicator strains.

Optimizing the design and synthesis of supported silver nanoparticles for low cost water disinfection

Silver nanoparticles (AgNPs) were successfully synthesized and impregnated on silica using chemical reduction methods. XPS and Ag K-edge XANES analysis revealed that the impregnation of AgNPs onto silica using a chitosan + sodium borohydride (NaBH4) method results in higher silver loading and Ag(0)/Ag(I) ratio compared to that obtained using NH3 + NaBH4/glucose methods. The effects of the dosage of chitosan on silver loading, Ag(I) release, and bactericidal activities of AgNP-impregnated silica were investigated, with results showing that, at high dosages of chitosan, Ag(I) released from AgNP-impregnated silica plays an important role in disinfection, while AgNP-mediated bactericidal action dominates at low dosages of chitosan. To further decrease the manufacturing cost, partially oxidized "black rice husk ash" containing substantial residual carbon was applied as AgNP support and found to lead to a greater degree of silver impregnation and to exhibit a longer disinfection lifetime than that of lower carbon content silica supports. On the basis of these findings, it is clear that considerable scope exists for careful optimization in the design and production of AgNP-based bactericidal materials for water treatment purposes.

A new silver based composite material for SPA water disinfection

A new composite material based on alumina (Al2O3) modified by two surface nanocoatings - titanium dioxide (TiO2) and silver (Ag) - was studied for spa water disinfection. Regarding the most common microorganisms in bathing waters, two non-pathogenic bacteria Escherichia coli (Gram-negative) and Staphylococcus epidermidis (Gram positive) were selected as surrogates for bacterial contamination. The bactericidal properties of the Al2O3-TiO2-Ag material were demonstrated under various operating conditions encountered in spa water (temperature: 22-37 °C, presence of salt: CaCO3 or CaCl2, high oxygen content, etc.). Total removal of 10(8) CFU mL(-1) of bacteria was obtained in less than 10 min with 16 g L(-1) of material. Best results were observed for both conditions: a temperature of 37 °C and under aerobic condition; this latest favouring Reactive Oxygen Species (ROS) generation. The CaCO3 salt had no impact on the bactericidal activity of the composite material and CaCl2 considerably stabilized the silver desorption from the material surface thanks to the formation of AgCl precipitate. Preliminary tests of the Al2O3-TiO2-Ag bactericidal behaviour in a continuous water flow confirmed that 2 g L(-1) of material eliminated more than 90% of a 2.0 × 10(8) CFU mL(-1) bacterial mixture after one water treatment recycle and reached the disinfection standard recommended by EPA (coliform removal = 6 log) within 22 h.

Silver-zeolite combined to polyphenol-rich extracts of Ascophyllum nodosum: potential active role in prevention of periodontal diseases

The purpose of this study was to evaluate various biological effects of silver-zeolite and a polyphenol-rich extract of A. nodosum (ASCOP) to prevent and/or treat biofilm-related oral diseases. Porphyromonas gingivalis and Streptococcus gordonii contribute to the biofilm formation associated with chronic periodontitis. In this study, we evaluated in vitro antibacterial and anti-biofilm effects of silver-zeolite (Ag-zeolite) combined to ASCOP on P. gingivalis and S. gordonii growth and biofilm formation capacity. We also studied the anti-inflammatory and antioxidant capacities of ASCOP in cell culture models. While Ag-zeolite combined with ASCOP was ineffective against the growth of S. gordonii, it showed a strong bactericidal effect on P. gingivalis growth. Ag-zeolite combined with ASCOP was able to completely inhibit S. gordonii monospecies biofilm formation as well as to reduce the formation of a bi-species S. gordonii/P. gingivalis biofilm. ASCOP alone was ineffective towards the growth and/or biofilm formation of S. gordonii and P. gingivalis while it significantly reduced the secretion of inflammatory cytokines (TNFα and IL-6) by LPS-stimulated human like-macrophages. It also exhibited antioxidant properties and decreased LPS induced lipid peroxidation in gingival epithelial cells. These findings support promising use of these products in future preventive or therapeutic strategies against periodontal diseases.

Comparison of antibacterial activities of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles

Core-shell type Ag@TiO2 nanoparticles were prepared by one pot simultaneous reduction of AgNO3 and hydrolysis of Ti (IV) isopropoxide and Ag@SiO2 core-shell nanoparticles were prepared by Stober's method. They were characterized by absorption, XRD, and HR-TEM techniques. XRD patterns show the presence of anatase form of TiO2 and amorphous form of SiO2 and the noble metal (Ag). High resolution transmission electron microscopy measurements revealed that their size is below 50 nm. The antibacterial properties of Ag@TiO2 and Ag@SiO2 core-shell nanoparticles against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were examined by the agar diffusion method. As a result E. coli and S. aureus were shown to be substantially inhibited by Ag@TiO2 and Ag@SiO2 core-shell nanoparticles. These results demonstrated that TiO2 and SiO2 supported on the surface of Ag NPs without aggregation was proved to have enhanced antibacterial activity.