Proteomic analysis of an Enterococcus faecalis mutant generated against the exposure to silver nanoparticles.

INTRODUCTION: Nanoparticles (NPs) have been widely studied as an alternative to antibiotic use due to their antimicrobial properties at lower concentrations. Enterococcus faecalis is a facultative Gram-positive microorganism inhabiting the gastrointestinal tract of humans and animals. It can also be present in other environments such as the oral cavity, water, sewage, soil and food. AIMS: We evaluated whether E. faecalis could develop resistance to silver NPs (AgNPs) after exposure to sublethal concentrations of the NPs. METHODS AND RESULTS: Proteomic analyses revealed that different pathways were activated during the acquired resistance under sublethal concentrations, and selected genes were validated by qPCR. CONCLUSIONS: The results of this study showed that E. faecalis is capable of generating resistance to AgNPs. SIGNIFICANCE AND IMPACT OF THE STUDY: To avoid the generation of resistance against AgNPs, future use of these NPs should be combined with other NPs prepared with different metals to prevent the dissemination of resistant strains.

Molecular Mechanisms of Bacterial Resistance to Metal and Metal Oxide Nanoparticles.

The increase in bacterial resistance to one or several antibiotics has become a global health problem. Recently, nanomaterials have become a tool against multidrug-resistant bacteria. The metal and metal oxide nanoparticles are one of the most studied nanomaterials against multidrug-resistant bacteria. Several in vitro studies report that metal nanoparticles have antimicrobial properties against a broad spectrum of bacterial species. However, until recently, the bacterial resistance mechanisms to the bactericidal action of the nanoparticles had not been investigated. Some of the recently reported resistance mechanisms include electrostatic repulsion, ion efflux pumps, expression of extracellular matrices, and the adaptation of biofilms and mutations. The objective of this review is to summarize the recent findings regarding the mechanisms used by bacteria to counteract the antimicrobial effects of nanoparticles.

Effect of Silver Nanoparticle-Added Pit and Fissure Sealant in the Prevention of Dental Caries in Children.

OBJECTIVE: The objective of this study was to evaluate the effects of pit and fissure sealant mixed with silver nanoparticles on dental caries, by means of monthly measurement of fluorescence with DIAGNOdent over six months. STUDY DESIGN: This study was divided in two phases: experimental and clinical. In the experimental phase, the adhesion and microleakage of the pit and fissure sealant experiment were evaluated. Two groups of 10 teeth, without serious carious lesions, were included. Conventional (group A) and silver nanoparticles (group B) were added to the pit and fissure sealant. For the clinical phase, a split-mouth study was performed on 40 children aged 6-10 years old with healthy, erupted permanent first molars. A conventional pit and fissure sealant or a silver nanoparticle-mixed sealant was randomly placed. Repeated measures analysis was performed. RESULTS: Conventional sealant presented an average microleakage of 30.6%, and the silver nanoparticle-mixed sealant showed 33.6% (P=NS). A three times greater reduction in fluorescence was found in the silver nanoparticles group compared to the conventional group (P<0.05). No sex- or age-based associations were found. CONCLUSIONS: The silver nanoparticle-mixed sealant reduced tooth demineralization significantly and likely increased remineralization, compared to the conventional sealant.

Anti-biofilm activity of silver nanoparticles against different microorganisms.

Biofilms confer protection from adverse environmental conditions and can be reservoirs for pathogenic organisms and sources of disease outbreaks, especially in medical devices. The goal of this research was to evaluate the anti-biofilm activities of silver nanoparticles (AgNPs) against several microorganisms of clinical interest. The antimicrobial activity of AgNPs was tested within biofilms generated under static conditions and also under high fluid shears conditions using a bioreactor. A 4-log reduction in the number of colony-forming units of Pseudomonas aeruginosa was recorded under turbulent fluid conditions in the CDC reactor on exposure to 100 mg ml(-1) of AgNPs. The antibacterial activity of AgNPs on various microbial strains grown on polycarbonate membranes is reported. In conclusion, AgNPs effectively prevent the formation of biofilms and kill bacteria in established biofilms, which suggests that AgNPs could be used for prevention and treatment of biofilm-related infections. Further research and development are necessary to translate this technology into therapeutic and preventive strategies.

Antibacterial activity, inflammatory response, coagulation and cytotoxicity effects of silver nanoparticles.

The incorporation of nanoparticles (NPs) in industrial and biomedical applications has increased significantly in recent years, yet their hazardous and toxic effects have not been studied extensively. Here, we studied the effects of 24 nm silver NPs (AgNPs) on a panel of bacteria isolated from medical devices used in a hospital intensive care unit. The cytotoxic effects were evaluated in macrophages and the expression of the inflammatory cytokines IL-6, IL-10 and TNF-α were quantified. The effects of NPs on coagulation were tested in vitro in plasma-based assays. We demonstrated that 24 nm AgNPs were effective in suppressing the growth of clinically relevant bacteria with moderate to high levels of antibiotic resistance. The NPs had a moderate inhibitory effect when coagulation was initiated through the intrinsic pathway. However, these NPs are cytotoxic to macrophages and are able to elicit an inflammatory response. Thus, beneficial and potential harmful effects of 24 nm AgNPs on biomedical devices must be weighed in further studies in vivo. From the Clinical Editor: The authors of this study demonstrate that gallic acid reduced 24 nm Ag NPs are effective in suppressing growth of clinically relevant antibiotic resistant bacteria. However, these NPs also exhibit cytotoxic properties to macrophages and may trigger an inflammatory response. Thus, the balance of beneficial and potential harmful effects must be weighed carefully in further studies.

Reusability in visible light of titanate nanotubes for the removal of organic pollutants: role of calcination temperature.

Titanate nanotubes (NTs) were synthesised by the hydrothermal method and later calcined at temperatures between 100-500°C. The calcined NTs were characterised and evaluated in the physicochemical adsorption of the safranin dye and photocatalytic degradation of caffeine. The materials calcined at low temperatures displayed a tubular structure and the H2Ti3O7 crystalline phase, which was transformed into anatase nanoparticles at 400°C. The NTs treated at 100°C showed the highest adsorption capacity (94%). Safranin was adsorbed through an ion-exchange mechanism, following the Langmuir isotherm and a pseudo-second-order kinetic model. While NTs calcined at lower temperatures were better for adsorption, the photocatalytic degradation of caffeine increased in samples calcined at higher temperatures with a maximum removal of 72%. The photocatalytic behaviour of the NT samples confirmed that the crystalline anatase structure in conjunction with structural OH groups enhanced the photocatalytic activity. The addition of isopropanol as a scavenger confirmed the important role played by the •OH radicals in the photocatalytic process. NTs calcined at 300°C were efficient for both adsorption and photocatalytic processes. Due to its efficiency, this sample was reused after dye adsorption for the photocatalytic degradation of caffeine under visible light due to its enhanced absorbance in the visible region. This research work shows the potential of NTs for wastewater purification.

Synergistic bactericidal activity of Ag-TiO2 nanoparticles in both light and dark conditions.

High-throughput screening was employed to evaluate bactericidal activities of hybrid Ag-TiO2 nanoparticles comprising variations in TiO2 crystalline phase, Ag content, and synthesis method. Hybrid Ag-TiO2 nanoparticles were prepared by either wet-impregnation or UV photo deposition onto both Degussa P25 and DuPont R902 TiO2 nanoparticles. The presence of Ag was confirmed by ICP, TEM, and XRD analysis. The size of Ag nanoparticles formed on anatase/rutile P25 TiO2 nanoparticles was smaller than those formed on pure rutile R902. When activated by UV light, all hybrid Ag-TiO2 nanoparticles exhibited stronger bactericidal activity than UV alone, Ag/UV, or UV/TiO2. For experiments conducted in the dark, bactericidal activity of Ag-TiO2 nanoparticles was greater than either bare TiO2 (inert) or pure Ag nanoparticles, suggesting that the hybrid materials produced a synergistic antibacterial effect unrelated to photoactivity. Moreover, less Ag(+) dissolved from Ag-TiO2 nanoparticles than from Ag nanoparticles, indicating the antibacterial activities of Ag-TiO2 was not only caused by releasing of toxic metal ions. It is clear that nanotechnology can produce more effective bactericides; however, the challenge remains to identify practical ways to take advantage of these exciting new material properties.

In vitro cytotoxicity of silver nanoparticles on human periodontal fibroblasts.

UNLABELLED: Silver nanoparticles (NNPs) are extensively used for all kinds of antimicrobial applications in medical research. Their efficacy has been demonstrated against Streptococcus mutans, which is associated with dental caries. However their cytotoxic effects on human periodontal tissue are not completely understood. OBJECTIVE: The aim of this study was to evaluate the possible toxic cellular effects of different concentrations and sizes of silver nanoparticles, less than 10 nm, 15-20 nm, and 80-100 nm, respectively, on human periodontal fibroblasts. STUDY DESIGN: Primary culture cells isolated from human periodontal tissue were exposed to 0-1,000 microM silver nanoparticles of each size for 24-, 72-, and 168-hour periods. Cytotoxicity was evaluated with a nonradioactive, soluble MTS/PMS assay. RESULTS: The results demonstrated that silver nanoparticles of less than 20 nm increased cytotoxicity in human periodontal fibroblasts in a dose- and time-dependent manner. CONCLUSION: The 80-100-nm-sized nanoparticles did not modify the viability of human primary culture cells.

Effect of surface characteristics on the antibacterial properties of titanium dioxide nanotubes produced in aqueous electrolytes with carboxymethyl cellulose.

Nanotubular structures were produced on a commercially pure titanium surface by anodization in an aqueous electrolyte that contained carboxymethyl cellulose and sodium fluoride. The internal diameters obtained were about 100, 48, and 9.5 nm, respectively. Several heat treatments at 200, 350, and 600°C were made to produce nanotubes with different titanium dioxide polymorphs (anatase, rutile). All tested surfaces were superhydrophilic, this behavior was maintained after at least 30 days, regardless of the heat treatment. Although in previous works the nanotube features effect on the bacteria behavior had been studied; this item still unclear. For the best of our knowledge, the effect of small internal diameters (about 10 nm) with and without heat treatment and with and without ultraviolet (UV) irradiation on the bacteria strains comportment has not been reported. From our results, both the internal diameter and the postanodized treatments have an effect on the bacteria strains comportment. All nanotubular coatings UV treated and heat treated at 350 and 600°C; despite they have different inner diameters, inhibit the bacteria growth of both Staphylococcus aureus and Pseudomonas aeruginosa strains. The nanotubular coatings obtained at 20 V and heat treated at 350°C produced the lower bacteria adhesion against both strains evaluated.

Atomic force microscopy observation of the enamel roughness and depth profile after phosphoric acid etching.

The aim was to compare the enamel surface roughness (ESR) and absolute depth profile (ADP) (mean peak-to-valley height) by atomic force microscopy (AFM) before and after using four different phosphoric acids. A total of 160 enamel samples from 40 upper premolars were prepared. The inclusion criterion was that the teeth have healthy enamel. Exclusion criteria included any of the following conditions: facial restorations, caries lesions, enamel hypoplasia and dental fluorosis. Evaluations of the ESR and ADP were carried out by AFM. The Mann-Whitney U-test was used to compare continuous variables and the Wilcoxon test was used to analyze the differences between before and after etching. There were statistically significant differences (P

Synthesis, characterization, and evaluation of antimicrobial and cytotoxic effect of silver and titanium nanoparticles.

Microbial resistance represents a challenge for the scientific community to develop new bioactive compounds. Nosocomial infections represent an enormous emerging problem, especially in patients with ambulatory treatment, which requires that they wear medical devices for an extended period of time. In this work, an evaluation of the antimicrobial activity of both silver and titanium nanoparticles was carried out against a panel of selected pathogenic and opportunistic microorganisms, some of them commonly associated with device-associated infections. Cytotoxicity assays monitoring DNA damage and cell viability were evaluated using human-derived monocyte cell lines. We show that silver-coated nanoparticles having a size of 20-25 nm were the most effective among all the nanoparticles assayed against the tested microorganisms. In addition, these nanoparticles showed no significant cytotoxicity, suggesting their use as antimicrobial additives in the process of fabrication of ambulatory and nonambulatory medical devices. FROM THE CLINICAL EDITOR: In this study, antimicrobial activity of silver and titanium nanoparticles was evaluated against a panel of selected pathogenic and opportunistic microorganisms. Silver-coated nanoparticles of 20-25 nm size were the most effective among all the nanoparticles without significant cytotoxicity, suggesting their use as antimicrobial additives in the process of fabrication of ambulatory and nonambulatory medical devices.

In vitro determination of the chromatic effect of a silver nanoparticles solution linked to the gantrez S-97 copolymer on tooth enamel.

Silver nanoparticles (NNPs), alone or in combination with the bioadhesive Gantrez S-97, have demonstrated their efficacy against Streptococcus mutans; however, it is not known if this combination changes the color of teeth. The aim of this work was to measure the color changes occurring after the use of a Gantrez-NNP combination on enamel tooth blocks. Two study groups were randomly formed: enamel blocks brushed with (a) the Gantrez-NNP combination and (b) conventional toothpaste, for 1 minute once daily for 4 weeks, then rinsed with distilled water and placed in thymol solution. Color changes in the enamel blocks were measured using a Minolta colorimeter CR300. Analysis of mixed models was performed with R 2.10.1 at a 95% confidence level, using the nonlinear mixed effects (NLME) package. The results showed that there were no color changes over time, only a high luminosity equal in both groups. Our study showed that the use of the Gantrez-NNP combination is safe with respect to dental esthetics in the control of S. mutans.

Bactericidal capacity of silver nanoparticles associated with Gantrez S-97 on Streptococcus mutans.

UNLABELLED: Dental caries is a worldwide public health problem. S mutans plays an important role in the etiology of caries. There have been studies that showed the antimicrobial properties of silver nanoparticles are an effective agent to diminish S. mutans. The objective of this study was to evaluate the bactericidal and bacteriostatic effects of silver nanoparticles in addition to the Gantrez S-27 copolymer, on S mutans. METHOD: We performed an in vitro experimental study using the liquid microdilution method in order to find the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) with the subcultures obtained. The mixture was obtained by preparing 98 microg/mL of silver nanoparticles (10(3)mol) with Gantrez S-27 2%, in distilled water The readings were performed 24 hours after incubation and on 3 consecutive days. The results showed an average MTC of 6.12 microg /mL and MBC of 6.12 microg /mL. CONCLUSION: The addition of Gantrez 2% to silver nanoparticles does not alter its antimicrobial effect.

Therapeutic Use of Silver Nanoparticles in the Prevention and Arrest of Dental Caries.

Dental caries is one of the major diseases of the oral cavity affecting humans worldwide. Different alternatives have been used for its control, but its incidence and prevalence are still high. On the other hand, silver has been used for centuries due to its antimicrobial properties. With advances in nanotechnology, the use and research in nanomaterials has increased, recently, and silver nanoparticles have become an essential part of the dental practice, giving materials physical and chemical improvements in their properties, used for their antibacterial capacity preventing and arresting dental caries. The objective of this review was to examine the use of silver nanoparticles, in the treatment of dental caries in the remineralization of teeth hard tissues, as well as the antimicrobial potential, cytotoxicity, and long-term effectiveness.

Effective control of biofilms by photothermal therapy using a gold nanorod hydrogel.

Biofilms are matrices synthesized by bacteria containing polysaccharides, DNA, and proteins. The development of biofilms in infectious processes can induce a chronic inflammatory response that may progress to the destruction of tissues. The treatment of biofilms is difficult because they serve as a bacterial mechanism of defense and high doses of antibiotics are necessary to treat these infections with limited positive results. It has been demonstrated that photothermal therapy using gold nanorods (AuNRs) is an attractive treatment because of its anti-biofilm activity. The purpose of this work was to generate a novel chitosan-based hydrogel embedded with AuNRs to evaluate its anti-biofilm activity. AuNRs were synthesized by the seed-mediated growth method and mixed with the chitosan-based hydrogel. Hydrogels were characterized and tested against two bacterial strains by irradiating the produced biofilm in the presence of the nanoformulation with a laser adjusted at the near infrared spectrum. In addition, the safety of the nanoformulation was assessed with normal human gingival fibroblasts. Results showed that a significant bacterial killing was measured when biofilms were exposed to an increase of 10°C for a short time of 2 min. Moreover, no cytotoxicity was measured when normal gingival fibroblasts were exposed to the nanoformulation using the bactericidal conditions. The development of the reported formulation can be used as a direct application to treat periodontal diseases or biofilm-produced bacteria that colonize the oral cavity.

Atmospheric Corrosion, Antibacterial Properties, and Toxicity of Silver Nanoparticles Synthesized by Two Different Routes.

Silver nanoparticles (AgNPs) have been widely employed or incorporated into different materials in biological application, due to their antibacterial properties. Therefore, antimicrobial capacity and cytotoxicity have been highly studied. However, most of these reports do not consider the possible corrosion of the nanomaterials during their exposure to atmospheric conditions since AgNPs undergo a transformation when they come in contact with a particular environment. Derived from this, the functionality and properties of the nanoparticles could decrease noticeably. The most common silver corrosion process occurs by the interaction of AgNPs with sulfur species (H2S) present in the atmospheric air, forming a corrosion layer of silver sulfide around the AgNPs, thus inhibiting the release of the ions responsible for the antimicrobial activity. In this work, AgNPs were synthesized using two different methods: one of them was based on a plant extract (Brickellia cavanillesii), and the other one is the well-known method using sodium borohydride (NaBH4). Chemical stability, corrosion, antibacterial activity, and toxic activity were evaluated for both sets of prepared samples, before and after exposition to atmospheric air for three months. The structural characterization of the samples, in terms of crystallinity, chemical composition, and morphology, evidenced the formation of link structures with nanobridges of Ag2S for non- "green" AgNPs after the air exposition and the intact preservation of silver core for the "green" sample. The antibacterial activity showed a clear improvement in the antimicrobial properties of silver in relation to the "green" functionalization, particle size control, and size reduction, as well as the preservation of the properties after air exposition by the effective "green" protection. The cytotoxicity effect of the different AgNPs against mononuclear cells showed a notable increment in the cell viability by the "green" functionalization.

The antimicrobial sensitivity of Streptococcus mutans to nanoparticles of silver, zinc oxide, and gold.

Dental caries is a worldwide public health problem for which Streptococcus mutans has been identified as the possible infectious etiology. In recent years nanotechnology has permitted the development of new properties of materials. The objective of this study was to compare the bactericidal and bacteriostatic effects of nanoparticles of silver, zinc oxide, and gold on S. mutans. We used the liquid dilution method to find the minimum inhibitory concentrations (MICs) and with subcultures obtained the minimum bactericidal concentrations (MBCs). For silver the results showed an average MIC of 4.86 +/- 2.71 microg/mL and MBC of 6.25 microg/mL; for zinc the MIC was 500 +/- 306.18 muicrog/mL and MBC of 500 microg/mL; the gold nanoparticles demonstrated an effect only at an initial concentration of 197 mug/mL. We established a higher antimicrobial effect against S. mutans of silver nanoparticles at lower concentrations than gold or zinc, which would allow achieving important clinical effects with a reduced toxicity.

Cytotoxic and Bactericidal Effect of Silver Nanoparticles Obtained by Green Synthesis Method Using Annona muricata Aqueous Extract and Functionalized with 5-Fluorouracil.

Nanomaterials obtained by green synthesis technologies have been widely studied in recent years owing to constitute cost-effective and environmental-friendly methods. In addition, there are several works that report the simultaneous performance of the reducer agent as a functionalizing agent, modifying the properties of the nanomaterial. As a simple and economical synthesis methodology, this work presents a method to synthesize silver nanoparticles (AgNPs) using Annona muricata aqueous extract and functionalized with 5-fluorouracil (5-FU). The processes of reduction, nucleation, and functionalization of the nanoparticles were analyzed by UV-Vis absorption spectroscopy, and it was found that they are the function of the contact time of the metal ions with the extract. The structural characterization was carried out by transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD). The antibacterial properties of the synthetized nanomaterials were tested using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli growth.

Clinical features, diagnosis and treatment of acute primary headaches at an emergency center: why are we still neglecting the evidence?

In order to analyze the clinical features, approach and treatment of patients with acute primary headaches seen at the Clinics Hospital of the Federal University of Uberlândia (HC-UFU) throughout 2005, the medical charts of 109 patients were evaluated through a standardized questionnaire as to age, gender, main diagnosis, characteristics of the headache attacks, diagnostic tests and treatment. Probable migraine was the most common type of primary headache (47.7%), followed by probable tension-type headache (37.6%), unspecified headache (11.9%), and headache not elsewhere classified (2.8%). As to characteristics of the crisis, the location of the pain was described in 86.2% of the patients. The most commonly used drugs for treatment of acute headache attacks were dipyrone (74.5%), tenoxicam (31.8%), diazepam (20.9%), dimenhydrate (10.9%), and metochlopramide (9.9%). The data collected are in agreement with those reported in literature. In most cases, treatment was not what is recommended by consensus or clinical studies with appropriate methodology. Therefore, we suggest the introduction of a specific acute headache management protocol which could facilitate the diagnosis, treatment and management of these patients.

Effects of silver nanoparticles on the bonding of three adhesive systems to fluorotic enamel.

The objective was to evaluate the effect of adding silver nanoparticles into three commercial adhesive systems (Excite™, Adper Prompt L-Pop™ and AdheSE™). Nanoparticles were prepared by a chemical method then mixed with the commercial adhesive systems. This was later applied to the fluorotic enamel, and then micro-tensile bond strength, contact angle measurements and scanning electron microscopy observations were conducted. The commercial adhesive systems achieved the lowest micro-tensile bond strength (Excite™: 11.0±2.1, Adper Prompt L-Pop™: 14.0±5.4 and AdheSE™: 16.0±3.0 MPa) with the highest adhesive failure mode related with the highest contact angle (46.0±0.6º, 30.0±0.5º and 28.0±0.4º respectively). The bond strength achieved in all the experimental adhesive systems (19.0±5.4, 20.0±4.0 and 19.0±3.5 MPa respectively) was statistically higher (p<0.05) than the control and showed the highest cohesive failures related to the lowest contact angle. Adding silver nanoparticles in order to decrease the contact angle improve the adhesive system wetting and its bond strength.