Physiologic actions of zinc related to inhibition of acid and alkali production by oral streptococci in suspensions and biofilms

Antimicrobial activity of Lactobacillus fermentum TcUESC01 against Streptococcus mutans UA159

Dental caries is a multifactorial chronic-infection disease, which starts with a bacterial biofilm formation caused mainly by Streptococcus mutans. The use of probiotics has shown numerous health benefits, including in the fight against oral diseases. Strains of Lactobacillus fermentum have already shown probiotic potential against S. mutans, but there are still few studies. Thus, the aim of our study was to evaluate the antimicrobial activity of the inoculum and metabolites produced by L. fermentum TcUESC01 against S. mutans UA159. For this, a growth curve of L. fermentum was performed and both the inoculum and the metabolites formed in the fermentation were tested against the growth of S. mutans UA159 in agar diffusion tests, and only its metabolites were tested to determine the minimum inhibitory concentration, minimal bactericidal concentration and inhibition of cell adhesion. Inhibition of biofilm formation, pH drop and proton permeability were also tested with the metabolites. The zone of inhibition began to be formed at 14 h and continued until 16 h. The inoculum containing L. fermentum also showed zone of inhibition. The MIC for the metabolites was 1280 mg/mL and the MBC was obtained with a concentration higher than the MIC equal to 5120 mg/mL. Half of the MIC concentration (640 mg/mL) was required to inhibit S. mutans adhesion to the surface of the microplates. In the biofilm analyzes, the treatment with the metabolites in the tested concentration was not able to reduce biomass, insoluble glucans and alkali soluble compared to the control biofilm (p > 0.05). The metabolites also did not affect acid production and acid tolerance of S. mutans cells in biofilms compared to saline group (p > 0.05). Lactic acid (50.38%) was the most abundant organic acid produced by L. fermentum. This is the first report showing that the metabolites produced by the Lactobacillus fermentum TcUESC01 have a potential to be used as an antimicrobial agent against S. mutans, showing anti-adherence and bactericidal activity against planktonic cells of S. mutans. Thus, further studies should be carried out in order to better understand the antimicrobial activity of metabolites of L. fermentum TCUESC01.

Zn2+-assisted photothermal therapy for rapid bacteria-killing using biodegradable humic acid encapsulated MOFs

Bacterial infection is seriously threatening human health all over the world, especially with the emergence of increasing drug-fast bacteria. It is urgent to develop a drug-free strategy to kill bacteria rapidly and efficiently. In this work, humic acid (HuA) encapsulated zeolitic imidazole framework-8 (ZIF-8) (HuA@ZIF-8) nanocomposites are synthesized by the in-situ growth of ZIF-8 on the surface of polyvinylpyrrolidone (PVP)-modified HuA. The synthesized nanocomposites possesses good photothermal effects, i.e., the temperature increased to 59.4 °C under the particle concentration of 1000 μg/mL with 10 min NIR irradiation. In addition, NIR irradiation can also control the release of Zn²⁺ from the composites. The good photothermal effects originate from HuA that can effectively absorb NIR light. The controlled release of Zn²⁺ is ascribed to the induced-dissociation of ZIF-8 under NIR light irradiation. The synergistic action of photothermal therapy and release of zinc ions contributes to the excellent antibacterial efficiency of HuA@ZIF-8 within a short time, i.e. 99.59 % and 99.37 % against Staphylococcus aureus and Escherichia coli with 20 min NIR irradiation, respectively. This work provides a promising strategy to develop a light-responsive platform with good biodegradability and low cost for rapid and effective sterilization.

A systematic review of the interaction and effects generated by antimicrobial metallic substituents in bone tissue engineering

Changes brought about by metal ions and metal nanoparticles within bacterial cells and the damage caused to the cellular membrane upon contact with negatively charged surface components.

Evaluation of a Zn-2Ag-1.8Au-0.2V Alloy for Absorbable Biocompatible Materials

Zinc (Zn) and Zn-based alloys have been proposed as a new generation of absorbable metals mainly owing to the moderate degradation behavior of zinc between magnesium and iron. Nonetheless, mechanical strength of pure Zn is relatively poor, making it insufficient for the majority of clinical applications. In this study, a novel Zn–2Ag–1.8Au–0.2V (wt.%) alloy (Zn–Ag–Au–V) was fabricated and investigated for use as a potential absorbable biocompatible material. Microstructural characterization indicated an effective grain-refining effect on the Zn alloy after a thermomechanical treatment. Compared to pure Zn, the Zn–Ag–Au–V alloy showed significantly enhanced mechanical properties, with a yield strength of 168 MPa, an ultimate tensile strength of 233 MPa, and an elongation of 17%. Immersion test indicated that the degradation rate of the Zn–Ag–Au–V alloy in Dulbecco’s phosphate buffered saline was approximately 7.34 ± 0.64 μm/year, thus being slightly lower than that of pure Zn. Biocompatibility tests with L929 and Saos-2 cells showed a moderate cytotoxicity, alloy extracts at 16.7%, and 10% concentration did not affect metabolic activity and cell proliferation. Plaque formation in vitro was reduced, the Zn–Ag–Au–V surface inhibited adhesion and biofilm formation by the early oral colonizer Streptococcus gordonii, indicating antibacterial properties of the alloy.

Systematical evolution on a Zn-Mg alloy potentially developed for biodegradable cardiovascular stents

To reduce the long-term side effects of permanent metallic stents, a new generation of cardiovascular stents called "biodegradable stents" is being extensively developed. Zinc has been considered as a promising candidate material for biodegradable cardiovascular stents due to its excellent biocompatibility and appropriate biodegradability. However, weak mechanical properties limit its further clinic application. In this study, hot extruded pure Zn and Zn-0.02 Mg alloy were prepared. Compared with pure Zn, Zn-0.02 Mg alloy showed more homogeneous microstructure, much smaller grain size and higher mechanical strength. Zn-0.02 Mg alloy presented uniform corrosion morphologies during the immersion process, and its corrosion rates was higher than that of pure Zn. Hemocompatibility results showed that the Zn-based alloy had extremely low hemolysis rate (0.74 ± 0.15%) and strong inhibitory effect on blood coagulation, platelet adhesion and aggregation. Zn-0.02 Mg alloy also exhibited excellent cytocompatibility. Its extracts could significantly promote the proliferation of endothelial cells. Moreover, the antibacterial activities of the Zn-based alloy were demonstrated by spread plate assay, live/dead viability assay and bacterial morphology observation. These results indicate that the extruded Zn-0.02 Mg alloy has a potential in biodegradable cardiovascular stents.

Air Abrasion With Bioactive Glass Eradicates Streptococcus mutans Biofilm From a Sandblasted and Acid-Etched Titanium Surface

Streptococcus mutans is able to form a high-affinity biofilm on material surfaces. S mutans has also been detected around infected implants. Bioactive glasses (BAGs) have been shown to possess antibacterial effects against S mutans and other microorganisms. This in vitro study was performed to investigate the influence of BAG air abrasion on S mutans biofilm on sandblasted and acid-etched titanium surfaces. Sandblasted and acid-etched commercially pure titanium discs were used as substrates for bacteria (n = 107). The discs were immersed in an S mutans solution and incubated for 21 hours to form an S mutans biofilm. Twenty colonized discs were subjected to air abrasion with Bioglass 45S5 (45S5 BAG), experimental zinc oxide containing BAG (Zn4 BAG), and inert glass. After the abrasion, the discs were incubated for 5 hours in an anaerobic chamber followed by an assessment of viable S mutans cells. Surface morphology was evaluation using scanning electron microscopy (n = 12). The thrombogenicity of the glass particle-abraded discs (n = 75) was evaluated spectrophotometrically using whole-blood clotting measurement at predetermined time points. Air abrasion with 45S5 and Zn4 BAG eradicated S mutans biofilm. Significantly fewer viable S mutans cells were found on discs abraded with the 45S5 or Zn4 BAGs compared with the inert glass (P < .001). No significant differences were found in thrombogenicity since blood clotting was achieved for all substrates at 40 minutes. Air abrasion with BAG particles is effective in the eradication of S mutans biofilm from sandblasted and acid-etched titanium surfaces. Zn4 and 45S5 BAGs had similar biofilm-eradicating effects, but Zn4 BAG could be more tissue friendly. In addition, the steady release of zinc ions from Zn4 may enhance bone regeneration around the titanium implant and may thus have the potential to be used in the treatment of peri-implantitis. The use of either BAGs did not enhance the speed of blood coagulation.

Inhibitory effect of zinc-containing desensitizer on bacterial biofilm formation and root dentin demineralization

This study compared the effect of a novel zinc containing, Caredyne Shield (CS), and a fluoroaluminocalciumsilicate-based, Nanoseal (NS) desensitizers on dentin tubule occlusion, inhibition of Streptococcus mutans (S. mutans) biofilm growth, and resistance to bacterial demineralization. Desensitizers were applied to simulated hypersensitive bovine dentin, with distilled water used as a control. S. mutans biofilms were grown on the surface of each specimen in an oral biofilm simulator. CS showed the least bacterial count and water insoluble glucan amount followed by NS. Transverse micro radiography revealed that both CS and NS showed significant reduction in mineral loss and lesion depth of the associated lesion. Scanning electron micrographs showed that the two desensitizers formed obvious depositions on the dentin surfaces, occlusion of tubules and mineral tag formation.

The Prospects for Biodegradable Zinc in Wound Closure Applications

Zinc is identified as a promising biodegradable metal along with magnesium and iron. In the last 5 years, considerable progress is made on understanding the mechanical properties, biodegradability, and biocompatibility of zinc and its alloys. A majority of these studies have focused on using zinc for absorbable cardiovascular and orthopedic device applications. However, it is likely that zinc is also suitable for other biomedical applications. In this work, the prospects for zinc in the fabrication of wound closure devices such as absorbable sutures, staples, and surgical tacks are critically assessed, with the aim of inspiring future research on biodegradable Zn for this medical application.

Titanium Dioxide Nanoparticles and Cetylpyridinium Chloride Enriched Glass-Ionomer Restorative Cement: A Comparative Study Assessing Compressive Strength and Antibacterial Activity

OBJECTIVE

To evaluate the addition of titanium dioxide (TiO₂) nanoparticles and cetylpyridinium chloride (CPC) on the compressive strength and antibacterial activity of conventional glass-ionomer cement (GIC).

STUDY DESIGN

TiO₂ nanoparticles enriched GIC was prepared by adding 3% TiO₂ nanoparticles (w/w) into the powder component of conventional GIC. CPC containing GIC was developed by incorporating 1% CPC (w/w) into conventional GIC powder. Samples were segregated into three groups: GIC with 3% TiO₂ nanoparticles, GIC with 1% CPC and unmodified conventional GIC. Compressive strength was assessed using the universal testing machine on cylindrical specimens made from each material. Antibacterial activity was assessed by measuring inhibition zones on Mitis Salivarius Bacitracin (MSB) agar inoculated with pure strain of Streptococcus mutans (S. mutans).

RESULTS

GIC containing TiO₂ nanoparticles exhibited significantly greater compressive strength as compared with CPC and conventional GIC groups (P < 0.01). However, there was no significant difference between the compressive strengths of CPC and conventional GIC group (P >0.05). Antibacterial activity was significantly greater for TiO₂ group than conventional GIC (P <0.05). CPC increased the antibacterial activity of conventional GIC, though not significantly.

CONCLUSION

The addition of 3% TiO₂ nanoparticles improves the compressive strength of GIC as well as its antibacterial activity against S. mutans.

Comparison of the Effects of Cytotoxicity and Antimicrobial Activities of Self-adhesive, Eugenol and Noneugenol Temporary and Traditional Cements on Gingiva and Pulp Living Cells

Aims and objectives:

The aim of this in vitro study was to investigate the antibacterial and cytotoxic effect of cements: zinc polycarboxylate, glass ionomer, self-adhesive resin cement, eugenol-containing and eugenol-free temporary cements.

Materials and methods:

The agar-diffusion test was carried out on 4 types of bacteria: Streptococcus mutans ( S. mutans; ATCC 35668), Streptococcus salivarius ( S. salivarius; ATCC 13419), Streptococcus sangius ( S. sangius; ATCC 10556), and Lactobacillus casei ( L. casei; ATCC 27139). Freshly prepared cement samples were placed on a brain heart infusion medium and left at 37°C for 24 hours in a CO2 incubator. Ampicillin disks of 10 mg were used as positive controls. Antimicrobial effects were determined using the zone of inhibition measurement in millimeters at 24 and 48 hours. Cytotoxicity was assessed through a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay (SERVA Electrophoresis GmbH, Heidelberg, Germany). To evaluate cell viability, an optical density microplate reader (Tecan™ Sunrise, Männedorf, Switzerland) was used at 24 and 48 hours at 570 and 630 nm, respectively.

Results:

Except the positive control group, the Adhesor luting cement showed a higher inhibitory effect on S. sangius and L. casei. RelyX Temp E temporary cement showed an inhibitory effect on S. sangius and L. casei, whereas the Cavex temporary cement showed an inhibitory effect on only S. sangius at 24 and 48 hours. At 100% concentration, Cavex temporary cement showed the least toxicity (23.6% pulp cell and 9.9% gingival cell) and highest cell viability (76.4% pulp cell and 90.1% gingival cell) at 24 hours. However, Meron, Adhesor, Panavia SA luting, and RelyX Temp E temporary cements showed the highest toxicity (above 94% gingival cell and 95% pulp cell) at 100% concentration.

Conclusions:

Meron, Adhesor, Panavia SA luting, and RelyX Temp E temporary cements may have a cytotoxic potential. None of the cements showed an inhibitory effect on S. mutan and S. salivarius, whereas Adhesor luting cement has a higher inhibitory effect than that of S. sangius and L. casei.

Detection of Residual Excess Zinc Oxide–Based Cement With Laser Fluorescence (DIAGNOdent): In Vitro Evaluation

Because of its importance in the development of peri-implant mucositis and peri-implantitis, detection of residual excess cement (REC) is often the focus of studies addressing cement-retained implant-supported restorations. The purpose of this study was to evaluate the sensitivity and specificity of laser fluorescence (DIAGNOdent) for detecting residual excess zinc oxidebased cement around dental implants. In this in vitro study, 15 tissue-level implants were embedded in acrylic resin. To simulate gingiva around the implants, the transgingival part of each implant was covered with a gingival mask silicon material. Cement (Tempobond; 1 × 1 × 1 mm) was applied to 30 areas, 4 mm below the gingival-mimicking line using a custom-made template. A DIAGNOdent laser device was used by 2 independent examiners to evaluate the presence or absence of cement in a selected area. The examiners were allowed to probe the gingival sulcus (2-mm depth) 2 times with a 5-minute interval between tests. The residual cement was recognized by gently walking the device tip around the implant. A detection score less than 16 indicated an absence of cement, and scores of 16 or greater indicated the presence of excess luting agent in the implant sulcus. The sensitivity and specificity of DIAGNOdent to detect REC in the sulcus were 100% and 96.67%, respectively. Based on our findings, we propose that DIAGNOdent could be used to detect REC in the sulcus of cement-retained implant supported restorations.

The influence of alloying and fabrication techniques on the mechanical properties, biodegradability and biocompatibility of zinc: A comprehensive review

Zinc has been identified as one of the most promising biodegradable metals along with magnesium and iron. Zinc appears to address some of the core engineering problems associated with magnesium and iron when applied to biomedical implant applications; hence the increase in the amount of research investigations on the metal in the last few years. In this review, the current state-of-the-art on biodegradable Zn, including recent developments, current opportunities and future directions of research are discussed. The discussions are presented with a specific focus on reviewing the relationships that exist between mechanical properties, biodegradability, and biocompatibility of zinc with alloying and fabrication techniques. This work hopes to guide future studies on biodegradable Zn that will help in advancing this field of research. STATEMENT OF SIGNIFICANCE: (i) The review offers an up-to-date and comprehensive review of the influence of alloying and fabrication technique on mechanical properties, biodegradability and biocompatibility of Zn; (ii) the work cites the most relevant biodegradable Zn fabrication processes including additive manufacturing techniques; (iii) the review includes a listing of research gap and future research directions for the field of biodegradable Zn.

Study of potential biomedical application of sol-gel derived Zn-doped SiO2-hydroxypropyl cellulose nanohybrids

A series of Zn-doped hybrid materials based on silica from tetraethoxysilane (TEOS) and hydroxypropyl cellulose (HPC) were prepared by a sol-gel route. The structure, morphology and thermal behavior of synthesized hybrids were characterized by infrared (IR) spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), transmission electron microscopy (TEM) and differential thermal analysis with thermogravimetric analysis (DTA/TG). The obtained materials were investigated for a potential biomedical application. The antibacterial properties of hybrids were investigated by measuring the inhibition zones formed around the materials containing different zinc content in presence of reference strains of Gram-positive and Gram-negative bacteria. The biocompatibility tests showed no cytotoxicity and genotoxicity, as well as no changes in actin cytoskeleton organization for hybrids with Zn content below 5 wt%.

Bactericidal ZnO glass-filled thermoplastic polyurethane and polydimethyl siloxane composites to inhibit biofilm-associated infections

This study investigates a novel approach to controlling biofilms of the most frequent pathogens implicated in the etiology of biomaterials-associated infections. New bactericidal filler based on a non-toxic glass, belonging to B2O3-SiO2-Al2O3-Na2O-ZnO system, was used to formulate composites of the most widely used polymers in biomedical applications [i.e. thermoplastic polyurethane (TPU) and polydimethyl siloxane (PDMS)], with varying percentage by weight of the bactericidal glass (5, 15, 25, 35, 50%). Glass-filled polymer composites show dramatically restricted bacterial colonisation and biofilm formation. They exhibit time- and dose-dependent killing, with maximal action at 5 days. The highest activity was found against S.epidermidis biofilm (99% of reduction), one of the most common cause of nosocomial infections. The tensile properties of the obtained glass-filled composites are comparable with the literature data concerning polymeric biomaterials for medical implants and devices. In addition, all the materials presented in this research, revealed an excellent biocompatibility. This was disclosed by cell viability values above 70%, none alteration on erythrocyte membrane or cell functionality in contact with materials (haemolytic index 0-2%), and absence of interferences in blood coagulation (intrinsic, extrinsic and final pathways).

Bi-functional titanium-polydopamine-zinc coatings for infection inhibition and enhanced osseointegration

The ideal orthopedic implant coating is expected to both inhibit microbial infection and promote osseointegration. In this study, Zn ions were immobilized on a Ti substrate via a polydopamine (PDA) chemical surface modification to prepare Ti-PDA-Zn coatings. Scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscope (EDS), X-ray photoelectron spectroscopy (XPS), contact analysis system, and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used to analyze the morphology, composition, wettability, and zinc ions release of the coatings. The Ti-PDA-Zn coatings demonstrated excellent antibacterial activities in vitro against both Staphylococcus aureus and Escherichia coli. The coatings additionally displayed good biocompatibility, as confirmed by cytoskeletal observations and cell viability assays. Furthermore, the in vivo results confirmed the excellent antibacterial properties and improved osseointegration capability of the Ti-PDA-Zn coating in the presence of S. aureus. The present findings indicate that the Ti-PDA-Zn coatings prepared herein have potential application in orthopedic implantation.

The ideal orthopedic implant coating is expected to both inhibit microbial infection and promote osseointegration.

Antimicrobial resistance due to the content of potentially toxic metals in soil and fertilizing products

Potentially toxic metals (PTM), along with PTM-resistant bacteria and PTM-resistance genes, may be introduced into soil and water through sewage systems, direct excretion, land application of biosolids (organic matter recycled from sewage, especially for use in agriculture) or animal manures as fertilizers, and irrigation with wastewater or treated effluents. In this review article, we have evaluated whether the content of arsenic (As), cadmium (Cd), chromium (CrIII + CrVI), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn) in soil and fertilizing products play a role in the development, spreading, and persistence of bacterial resistance to these elements, as well as cross- or co-resistance to antimicrobial agents. Several of the articles included in this review reported the development of resistance against PTM in both sewage and manure. Although PTM like As, Hg, Co, Cd, Pb, and Ni may be present in the fertilizing products, the concentration may be low since they occur due to pollution. In contrast, trace metals like Cu and Zn are actively added to animal feed in many countries. In several studies, several different bacterial species were shown to have a reduced susceptibility towards several PTM, simultaneously. However, neither the source of resistant bacteria nor the minimum co-selective concentration (MCC) for resistance induction are known. Co- or cross-resistance against highly important antimicrobials and critically important antimicrobials were identified in some of the bacterial isolates. This suggest that there is a genetic linkage or direct genetic causality between genetic determinants to these widely divergent antimicrobials, and metal resistance. Data regarding the routes and frequencies of transmission of AMR from bacteria of environmental origin to bacteria of animal and human origin were sparse. Due to the lack of such data, it is difficult to estimate the probability of development, transmission, and persistence of PTM resistance. Abbreviations: PTM: potentially toxic metals; AMR: antimicrobial resistance; ARG: antimicrobial resistance gene; MCC: minimum co-selective concentration; MDR: multidrug resistance; ARB: antimicrobial resistant bacteria; HGT: horizontal gene transfer; MIC: minimum inhibitory concentration.

Penetration of an antimicrobial zinc-sugar alcohol complex into Streptococcus mutans biofilms

Mature biofilms are highly resistant to antimicrobial agents due to the presence of extracellular polymeric substances (EPS), which inhibit the penetration of external molecules. In this study, we developed a coordination compound consisting of zinc chloride and erythritol that exhibits penetrating and bactericidal activity against Streptococcus mutans biofilms. An in vitro biofilm model was established in microplates, and bactericidal activity against biofilms was evaluated using an Alamar blue assay. The cause of the antimicrobial activity of the zinc-erythritol mixture on mature biofilms was demonstrated using fast atom bombardment-mass spectrometry, confocal laser scanning microscopy and atomic force microscopy. We demonstrated that zinc chloride spontaneously formed cationic complexes with erythritol in water. The zinc-erythritol complexes reduced intra- and inter-molecular interactions between bacterial exopolysaccharides, a major component of EPS. This activity was confirmed by measuring the attenuation of the hardness of dried polysaccharides isolated from S. mutans biofilms. The reduction in the interactions between polysaccharides allowed the complexes to penetrate into biofilms and kill the embedded bacteria. While approximately 13% of biofilm-associated microbes were killed by a 10 min treatment with 6.6 mM zinc chloride, 45% were killed when a solution containing 19.8 mM erythritol and 6.6 mM zinc chloride was used. This strategy of leveraging the coordination properties of metal ions with sugar alcohols provides a simple way to effectively remove mature biofilms using only conventional substances without the need for intricate chemical synthesis processes.

A systematic review on antibacterial activity of zinc against Streptococcus mutans

OBJECTIVES

The aim of this study was to systematically review the growth inhibition effectiveness of zinc against Streptococcus mutans. The main question was, "Does the zinc inhibit the growth of oral Streptococcus mutans in vitro?

METHODS

Literature search on PubMed, Medline, and science direct databases was carried out for in vitro studies published in English from 1990 to 2016, and the reported outcomes of minimum inhibitory concentration (MIC), minimum bactericidal concentrations (MBC), zone of inhibition (ZOI) and bacterial count method using colony forming unit (CFU) were used to assess the antibacterial effectiveness of zinc.

RESULTS

Seventeen studies were included in this review. Seven studies reported MIC and MBC. Four studies reported ZOI, and eight studies reported CFU. MIC values using zinc chloride and zinc oxide nanoparticles were ranged from 0.025 to 0.2 mM and 0.390 to 500 ± 306.18 µg/ml respectively. MBC values using zinc oxide nanoparticles have ranged from 3.125 to 500 µg/ml. ZOI ranged from no inhibition zone to 21 ± 1.4 mm using 23.1% zinc oxide. A considerable reduction in the bacterial count was reported after adding zinc. However, only two studies have reported no inhibitory effect of zinc.

CONCLUSION

This review indicated a significant growth inhibition effectiveness of zinc even at lower concentrations which indicate it's safely to be used in oral health products.

Bio-sourced phosphoprotein-based synthesis of silver-doped macroporous zinc phosphates and their antibacterial properties

The usual sources of phosphorus for metal phosphates are obtained from phosphate rocks, of which resources are depleted. As a substitute for these mineral sources, an original method of synthesis has been developed to prepare macroporous zinc phosphates using casein phosphoprotein. This bio-sourced reactant plays during the synthesis the roles of both a phosphorus source and a reducing agent for silver nanoparticles. Thus, zinc phosphates loaded with different Ag contents (up to 6.4 wt%) are prepared via hydrothermal treatment at 100 °C. Silver nanoparticles co-crystallized with hopeite, Zn3(PO4)2 and/or Zn2P2O7. In addition, casein induces porosity within the zinc phosphate framework and provides macropores (diameter of >50 nm) during calcination. The antibacterial properties against Escherichia coli K12 bacteria of Ag-containing and Ag-free porous zinc phosphates (calcined at 750 °C) were also tested for the first time.

Effect of incorporation of zinc oxide nanoparticles on mechanical properties of conventional glass ionomer cements

Aim:

The aim of this study is to investigate the physical properties of conventional and resin-modified glass ionomer cements (GICs) compared to GICs supplemented with zinc oxide (ZnO) nanofiller particles at 5% (w/w).

Methods:

In this in vitro study, ZnO nanoparticles of different morphologies (nanospherical, nanorod, and nanoflower) were incorporated to glass ionomer powder. The samples were subjected to the flexural strength (n = 20) and surface hardness test (n = 12) using a universal testing machine and a Vickers hardness machine, respectively. Surface analysis and crystal structure of samples were performed with scanning electron microscope and X-radiation diffraction, respectively. The data were analyzed using one-way ANOVA, Shapiro–Wilk, and Tukey's tests (P < 0.05).

Results:

Flexural strength of glass ionomer containing nanoparticles was not significantly different from the control group (P > 0.05). The surface hardness of the glass ionomer containing nanospherical or nanoflower ZnO was significantly lower than the control group (P < 0.05). However, the surface hardness of glass ionomer containing nanorod ZnO was not significantly different from the control group (P = 0.868).

Conclusions:

Incorporation of nanospherical and nanoflower ZnO to glass ionomer decreased their surface hardness, without any changes on their flexural strength. Incorporation of nanorod ZnO particles caused no effect on the mechanical properties.

Production and Characterization of Superhydrophobic and Antibacterial Coated Fabrics Utilizing ZnO Nanocatalyst

Dirt and microorganisms are the major problems in textiles which can generate unpleasant odor during their growth. Here, zinc oxide (ZnO) nanoparticles prepared by sol-gel method were loaded on the cotton fabrics using spin coating technique to enhance their antimicrobial properties and water repellency. The effects of ZnO precursor concentration, precursor solution pH, number of coating runs, and Mg doping percent on the structures, morphologies, and water contact angles (WCA) of the ZnO-coated fabrics were addressed. At 0.5 M concentration and pH7, more homogeneous and smaller ZnO nanoparticles were grown along the preferred (0 0 2) direction and uniformly distributed on the fabric with a crystallite size 17.98 nm and dislocation density 3.09 × 10-3 dislocation/nm2. The substitution of Zn 2+ with Mg 2+ ions slightly shifted the (002) peak position to a higher angle. Also, the zeta potential and particle size distribution were measured for ZnO nanoparticle suspension. A superhydrophobic WCA = 154° was measured for the fabric that coated at 0.5 M precursor solution, pH 7, 20 runs and 0% Mg doping. Moreover, the antibacterial activities of the ZnO-coated fabric were investigated against some gram-positive and gram-negative bacteria such as Salmonella typhimurium, Klebsiella pneumonia, Escherichia coli, and Bacillus subtilis.

Electro-chemical deposition of nano hydroxyapatite-zinc coating on titanium metal substrate

BACKGROUND

Titanium is an inert metal that does not induce osteogenesis and has no antibacterial properties; it is proposed that hydroxyapatite coating can enhance its bioactivity, while zinc can contribute to antibacterial properties and improve osseointegration.

AIMS

A nano-sized hydroxyapatite-zinc coating was deposited on commercially pure titanium using an electro-chemical process, in order to increase its surface roughness and enhance adhesion properties.

METHODS

The hydroxyapatite-zinc coating was attained using an electro-chemical deposition in a solution composed of a naturally derived calcium carbonate, di-ammonium hydrogen phosphate, with a pure zinc metal as the anode and titanium as the cathode. The applied voltage was -2.5 for 2 h at a temperature of 85 °C. The resultant coating was characterized for its surface morphology and chemical composition using a scanning electron microscope (SEM), energy dispersive x-ray spectroscope (EDS), and Fourier transform infrared (FT-IR) spectrometer. The coated specimens were also evaluated for their surface roughness and adhesion quality.

RESULTS

Hydroxyapatite-zinc coating had shown rosette-shaped, homogenous structure with nano-size distribution, as confirmed by SEM analysis. FT-IR and EDS proved that coatings are composed of hydroxyapatite (HA) and zinc. The surface roughness assessment revealed that the coating procedure had significantly increased average roughness (Ra) than the control, while the adhesive tape test demonstrated a high-quality adhesive coat with no laceration on tape removal.

CONCLUSIONS

The developed in vitro electro-chemical method can be employed for the deposition of an even thickness of nano HA-Zn adhered coatings on titanium substrate and increases its surface roughness significantly.

Antibacterial and bioactive coatings on titanium implant surfaces

Various surface modifications have been tried for enhancing osseointegration of the dental implants like mechanical and/or chemical treatments and deposition of calcium phosphate coatings. The objective of this research was to develop calcium-phosphate based thin coatings with antibacterial and bioactive properties for potential application in dental implants. Titanium (Ti) discs were immersed in different calcifying solutions: CaP (positive control), F-CaP, Zn-CaP, and FZn-CaP and incubated for 24 h. Negative control was uncoated Ti discs. Coated surfaces were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Antibacterial properties were tested using Porphyromonas gingivalis because of its strong association with periodontal and peri-implant infections. Bacterial adhesion and colonization were studied at different timepoints. The coated surfaces had compositional characteristics similar to that of bone mineral and they inhibited the growth, colonization and adherence of P. gingivalis, resulted in reduced thickness of biofilms and bacterial inhibition in the culture medium as compared to the positive and negative controls (p < 0.05). There was no significant difference between the experimental groups (p > 0.05). It has been previously demonstrated that these coatings have excellent in vitro bioactivity (formed carbonate hydroxyapatite when immersed in a simulated body fluid). Such coatings can enhance osseointegration and prevent infection in implants, thereby improving the success rates of implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2218-2227, 2017.

Transition Metal Homeostasis in Streptococcus pyogenes and Streptococcus pneumoniae

Trace metals such as Fe, Mn, Zn and Cu are essential for various biological functions including proper innate immune function. The host immune system has complicated and coordinated mechanisms in place to either starve and/or overload invading pathogens with various metals to combat the infection. Here, we discuss the roles of Fe, Mn and Zn in terms of nutritional immunity, and also the roles of Cu and Zn in metal overload in relation to the physiology and pathogenesis of two human streptococcal species, Streptococcus pneumoniae and Streptococcus pyogenes. S. pneumoniae is a major human pathogen that is carried asymptomatically in the nasopharynx by up to 70% of the population; however, transition to internal sites can cause a range of diseases such as pneumonia, otitis media, meningitis and bacteraemia. S. pyogenes is a human pathogen responsible for diseases ranging from pharyngitis and impetigo, to severe invasive infections. Both species have overlapping capacity with respect to metal acquisition, export and regulation and how metal homeostasis relates to their virulence and ability to invade and survive within the host. It is becoming more apparent that metals have an important role to play in the control of infection, and with further investigations, it could lead to the potential use of metals in novel antimicrobial therapies.

Research on a Zn-Cu alloy as a biodegradable material for potential vascular stents application

Zn-based alloys have been viewed as new potential materials for biodegradable implants, such as cardiovascular stents, mainly in consideration of their lower corrosion rate when compared with that of Mg alloys. In this study we developed a new Zinc-4wt.%Copper (Zn-4Cu) alloy as a biodegradable material. Hot extrusion was applied to Zn-4Cu to refine the microstructure and consequently improve its mechanical properties and corrosion resistance. After extrusion, dendritic CuZn5 phases were broken and distributed along the extrusion direction. The grains were refined obviously due to dynamical recrystallization. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the as-extruded alloy are 250±10MPa, 270±10MPa and 51±2%, respectively. The corrosion rate of the as-extruded alloy in Hank's solution is about 9.41(±1.34)μmyear(-1). In vitro evaluation shows that Zn-4Cu presents acceptable toxicity to human endothelial cells, and could effectively inhibit bacteria adhesion and biofilm formation. The present study indicates that the as-extruded Zn-4Cu alloy exhibits excellent strength and ductility, uniform and slow degradation, good biocompatibility and significant antibacterial effect, which make it an excellent candidate material for biodegradable implants, especially for cardiovascular stents application.

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.

Using adjuvants and environmental factors to modulate the activity of antimicrobial peptides

The increase in antibiotic resistant and multi-drug resistant bacterial infections has serious implications for the future of health care. The difficulty in finding both new microbial targets and new drugs against existing targets adds to the concern. The use of combination and adjuvant therapies are potential strategies to counter this threat. Antimicrobial peptides (AMPs) are a promising class of antibiotics (ABs), particularly for topical and surface applications. Efforts have been directed toward a number of strategies, including the use of conventional ABs combined with AMPs, and the use of potentiating agents to increase the performance of AMPs. This review focuses on combination strategies such as adjuvants and the manipulation of environmental variables to improve the efficacy of AMPs as potential therapeutic agents. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Synergistic effect of a biodegradable Mg–Zn alloy on osteogenic activity and anti-biofilm ability: an in vitro and in vivo study

It is desirable for orthopaedic implants to possess good osteointegration and anti-biofilm ability simultaneously for the prevention of implant associated infections and promotion of osteointegration.

Calcium fluoride nanoparticles induced suppression of Streptococcus mutans biofilm: an in vitro and in vivo approach

Biofilm formation on the tooth surface is the root cause of dental caries and periodontal diseases. Streptococcus mutans is known to produce biofilm which is one of the primary causes of dental caries. Acid production and acid tolerance along with exopolysaccharide (EPS) formation are major virulence factors of S. mutans biofilm. In the current study, calcium fluoride nanoparticles (CaF2-NPs) were evaluated for their effect on the biofilm forming ability of S. mutans in vivo and in vitro. The in vitro studies revealed 89 % and 90 % reduction in biofilm formation and EPS production, respectively. Moreover, acid production and acid tolerance abilities of S. mutans were also reduced considerably in the presence of CaF2-NPs. Confocal laser scanning microscopy and transmission electron microscopy images were in accordance with the other results indicating inhibition of biofilm without affecting bacterial viability. The qRT-PCR gene expression analysis showed significant downregulation of various virulence genes (vicR, gtfC, ftf, spaP, comDE) associated with biofilm formation. Furthermore, CaF2-NPs were found to substantially decrease the caries in treated rat groups as compared to the untreated groups in in vivo studies. Scanning electron micrographs of rat's teeth further validated our results. These findings suggest that the CaF2-NPs may be used as a potential antibiofilm applicant against S. mutans and may be applied as a topical agent to reduce dental caries.

Addition of Zn to the ternary Mg-Ca-Sr alloys significantly improves their antibacterial property

Most of the magnesium (Mg) alloys possess excellent biocompatibility, mechanical property and biodegradability in orthopedic applications. However, these alloys may suffer from bacterial infections due to their insufficient antibacterial capability. In order to reduce the post-surgical infections, a series of biocompatible Mg-1Ca-0.5Sr-xZn (x=0, 2, 4, 6) alloys were fabricated with the addition of antibacterial Zn with variable content and evaluated in terms of their biocompatibility and antibacterial property. The in vitro corrosion study showed that Mg-1Ca-0.5Sr-6Zn alloys exhibited a higher hydrogen evolution volume after 100 h immersion and resulted in a higher pH value of the immersion solution. Our work indicated that Zn-containing Mg alloys exhibited good biocompatibility with high cell viability. The antibacterial studies reveal that the number of bacteria adhered on all of these Mg alloy samples diminished remarkably compared to the Ti-6Al-4V control group. We also found that the proliferation of the bacteria was inhibited by these Mg alloys extracts. Among the prepared alloys, Mg-1Ca-0.5Sr-6Zn alloy not only exhibited a strong antibacterial effect, but also promoted the proliferation of MC3T3-E1 osteoblasts, suggesting that it is a promising alloy with both good antibacterial property and good biocompatibility for use as an orthopedic implant.

Enhanced antibacterial properties, biocompatibility, and corrosion resistance of degradable Mg-Nd-Zn-Zr alloy

Magnesium (Mg), a potential biodegradable material, has recently received increasing attention due to its unique antibacterial property. However, rapid corrosion in the physiological environment and potential toxicity limit clinical applications. In order to improve the corrosion resistance meanwhile not compromise the antibacterial activity, a novel Mg alloy, Mg-Nd-Zn-Zr (Hereafter, denoted as JDBM), is fabricated by alloying with neodymium (Nd), zinc (Zn), zirconium (Zr). pH value, Mg ion concentration, corrosion rate and electrochemical test show that the corrosion resistance of JDBM is enhanced. A systematic investigation of the in vitro and in vivo antibacterial capability of JDBM is performed. The results of microbiological counting, CLSM, SEM in vitro, and microbiological cultures, histopathology in vivo consistently show JDBM enhanced the antibacterial activity. In addition, the significantly improved cytocompatibility is observed from JDBM. The results suggest that JDBM effectively enhances the corrosion resistance, biocompatibility and antimicrobial properties of Mg by alloying with the proper amount of Zn, Zr and Nd.

Killing mechanism of stable N-halamine cross-linked polymethacrylamide nanoparticles that selectively target bacteria

Increased resistance of bacteria to disinfection and antimicrobial treatment poses a serious public health threat worldwide. This has prompted the search for agents that can inhibit both bacterial growth and withstand harsh conditions (e.g., high organic loads). In the current study, N-halamine-derivatized cross-linked polymethacrylamide nanoparticles (NPs) were synthesized by copolymerization of the monomer methacrylamide (MAA) and the cross-linker monomer N,N-methylenebis(acrylamide) (MBAA) and were subsequently loaded with oxidative chlorine using sodium hypochlorite (NaOCl). The chlorinated NPs demonstrated remarkable stability and durability to organic reagents and to repetitive bacterial loading cycles as compared with the common disinfectant NaOCl (bleach), which was extremely labile under these conditions. The antibacterial mechanism of the cross-linked P(MAA-MBAA)-Cl NPs was found to involve generation of reactive oxygen species (ROS) only upon exposure to organic media. Importantly, ROS were not generated upon suspension in water, revealing that the mode of action is target-specific. Further, a unique and specific interaction of the chlorinated NPs with Staphylococcus aureus was discovered, whereby these microorganisms were all specifically targeted and marked for destruction. This bacterial encircling was achieved without using a targeting module (e.g., an antibody or a ligand) and represents a highly beneficial, natural property of the P(MAA-MBAA)-Cl nanostructures. Our findings provide insights into the mechanism of action of P(MAA-MBAA)-Cl NPs and demonstrate the superior efficacy of the NPs over bleach (i.e., stability, specificity, and targeting). This work underscores the potential of developing sustainable P(MAA-MBAA)-Cl NP-based devices for inhibiting bacterial colonization and growth.

The antimicrobial sensitivity of Streptococcus mutans and Streptococcus sangius to colloidal solutions of different nanoparticles applied as mouthwashes

Background:

Metal nanoparticles have been recently applied in dentistry because of their antibacterial properties. This study aimed to evaluate antibacterial effects of colloidal solutions containing zinc oxide (ZnO), copper oxide (CuO), titanium dioxide (TiO₂) and silver (Ag) nanoparticles on Streptococcus mutans and Streptococcus sangius and compare the results with those of chlorhexidine and sodium fluoride mouthrinses.

Materials and Methods:

After adding nanoparticles to a water-based solution, six groups were prepared. Groups I to IV included colloidal solutions containing nanoZnO, nanoCuO, nanoTiO₂ and nanoAg, respectively. Groups V and VI consisted of 2.0% sodium fluoride and 0.2% chlorhexidine mouthwashes, respectively as controls. We used serial dilution method to find minimum inhibitory concentrations (MICs) and with subcultures obtained minimum bactericidal concentrations (MBCs) of the solutions against S. mutans and S. sangius. The data were analyzed by analysis of variance and Duncan test and P < 0.05 was considered as significant.

Results:

The sodium fluoride mouthrinse did not show any antibacterial effect. The nanoTiO₂-containing solution had the lowest MIC against both microorganisms and also displayed the lowest MBC against S. mutans (P < 0.05). The colloidal solutions containing nanoTiO₂ and nanoZnO showed the lowest MBC against S. sangius (P < 0.05). On the other hand, chlorhexidine showed the highest MIC and MBC against both streptococci (P < 0.05).

Conclusion:

The nanoTiO₂-containing mouthwash proved to be an effective antimicrobial agent and thus it can be considered as an alternative to chlorhexidine or sodium fluoride mouthrinses in the oral cavity provided the lack of cytotoxic and genotoxic effects on biologic tissues.

The bifunctional regulation of interconnected Zn-incorporated ZrO2 nanoarrays in antibiosis and osteogenesis

Bifunctional regulation in antibiosis and osteogenesis is obtained using well-organized Zn-incorporated ZrO₂ nanoarrays with interconnected internal space.

α-Mangostin disrupts the development of Streptococcus mutans biofilms and facilitates its mechanical removal

α-Mangostin (αMG) has been reported to be an effective antimicrobial agent against planktonic cells of Streptococcus mutans, a biofilm-forming and acid-producing cariogenic organism. However, its anti-biofilm activity remains to be determined. We examined whether αMG, a xanthone purified from Garcinia mangostana L grown in Vietnam, disrupts the development, acidogenicity, and/or the mechanical stability of S. mutans biofilms. Treatment regimens simulating those experienced clinically (twice-daily, 60 s exposure each) were used to assess the bioactivity of αMG using a saliva-coated hydroxyapatite (sHA) biofilm model. Topical applications of early-formed biofilms with αMG (150 µM) effectively reduced further biomass accumulation and disrupted the 3D architecture of S. mutans biofilms. Biofilms treated with αMG had lower amounts of extracellular insoluble and intracellular iodophilic polysaccharides (30-45%) than those treated with vehicle control (P<0.05), while the number of viable bacterial counts was unaffected. Furthermore, αMG treatments significantly compromised the mechanical stability of the biofilm, facilitating its removal from the sHA surface when subjected to a constant shear stress of 0.809 N/m2 (>3-fold biofilm detachment from sHA vs. vehicle-treated biofilms; P<0.05). Moreover, acid production by S. mutans biofilms was disrupted following αMG treatments (vs. vehicle-control, P<0.05). The activity of enzymes associated with glucan synthesis, acid production, and acid tolerance (glucosyltransferases B and C, phosphotransferase-PTS system, and F1F0-ATPase) were significantly inhibited by αMG. The expression of manL, encoding a key component of the mannose PTS, and gtfB were slightly repressed by αMG treatment (P<0.05), while the expression of atpD (encoding F-ATPase) and gtfC genes was unaffected. Hence, this study reveals that brief exposures to αMG can disrupt the development and structural integrity of S. mutans biofilms, at least in part via inhibition of key enzymatic systems associated with exopolysaccharide synthesis and acidogenicity. αMG could be an effective anti-virulence additive for the control and/or removal of cariogenic biofilms.

Deletion of the znuA virulence factor attenuates Actinobacillus pleuropneumoniae and confers protection against homologous or heterologous strain challenge

The znuA gene is known to be important for growth and survival in Escherichia coli, Haemophilus spp., Neisseria gonorrhoeae, and Pasteurella multocida under low Zn(2+) conditions. This gene is also present in Actinobacillus pleuropneumoniae serotype 1; therefore, the aim of this study was to investigate the existence of a similar role for the znuA gene in the growth and virulence of this organism. A precisely defined ΔznuA deletion mutant of A. pleuropneumoniae was constructed based on the sequence of the wild-type SLW01 using transconjugation and counterselection. This mutation was found to be lethal in low-Zn(2+) medium. Furthermore, the ΔznuA mutant strain exhibited attenuated virulence (≥22-fold) as well as reduced mortality and morbidity in a murine (Balb/C) model of infection. The majority of the bacteria were cleared from the lungs within 2 weeks. The ΔznuA mutant strain caused no adverse effects in pigs at doses of up to 1.0×10(9) CFU/mL. The ΔznuA mutant strain induced a significant immune response and conferred 80% and 100% protection on immunised pigs against challenge with A. pleuropneumoniae strains belonging to homologous or heterologous serovars, respectively, compared to the blank controls. The data obtained in this study indicate the potential of the mutant ΔznuA strain for development as a live vaccine capable of inducing reliable cross-serovar protection following intratracheal immunisation.

Withania somnifera attenuates acid production, acid tolerance and extra-cellular polysaccharide formation of Streptococcus mutans biofilms

Withania somnifera (Ashwagandha) is a plant of the Solanaceae family. It has been widely used as a remedy for a variety of ailments in India and Nepal. The plant has also been used as a controlling agent for dental diseases. The aim of the present study was to evaluate the activity of the methanol extract of W. somnifera against the physiological ability of cariogenic biofilms and to identify the components of the extract. To determine the activity of the extract, assays for sucrose-dependent bacterial adherence, glycolytic acid production, acid tolerance, and extracellular polysaccharide formation were performed using Streptococcus mutans biofilms. The viability change of S. mutans biofilms cells was also determined. A phytochemical analysis of the extract was performed using TLC and LC/MS/MS. The extract showed inhibitory effects on sucrose-dependent bacterial adherence (≥ 100 μg/ml), glycolytic acid production (≥ 300 μg/ml), acid tolerance (≥ 300 μg/ml), and extracellular polysaccharide formation (≥ 300 μg/ml) of S. mutans biofilms. However, the extract did not alter the viability of S. mutans biofilms cells in all concentrations tested. Based on the phytochemical analysis, the activity of the extract may be related to the presence of alkaloids, anthrones, coumarines, anthraquinones, terpenoids, flavonoids, and steroid lactones (withanolide A, withaferin A, withanolide B, withanoside IV, and 12-deoxy withastramonolide). These data indicate that W. somnifera may be a potential agent for restraining the physiological ability of cariogenic biofilms.

Synthesis of TiO2 nanotubes with ZnO nanoparticles to achieve antibacterial properties and stem cell compatibility

To endow titanium (Ti) with antibacterial properties, different concentrations of zinc oxide (ZnO) nanoparticles were decorated on anodized titanium dioxide (TiO2) nanotubes by a simple hydrothermal treatment method. The particle sizes of ZnO, which were evenly distributed and tightly adherent to the walls of the Ti nanotubes, ranged from 20-50 nm. Results from this study showed that Zn was released from the TiO2 nanotubes in a constant, slow, and biologically inspired manner. Importantly, the results showed that the ZnO decorated TiO2 nanotubular samples inhibited Streptococcus mutants and Porphyromonas gingivalis growth compared to control unmodified Ti samples. Specifically, S. mutants and P. gingivalis growth were both reduced 45-85% on the ZnO decorated Ti samples compared to Ti controls after 7 days of culture. When examining the mechanism of action, it has been further found for the first time that the ZnO decorated Ti samples inhibited the expression of Streptococcus mutans bacterial adhesion genes. Lastly, the results showed that the same samples which decreased bacterial growth the most (0.015 M precursor Zn(NO3)2 samples) did not inhibit mesenchymal stem cell growth compared to Ti controls for up to 7 days. In summary, results from this study showed that compared to plain TiO2 nanotubes, TiO2 decorated with 0.015 M ZnO provided unprecedented antibacterial properties while maintaining the stem cell proliferation capacity necessary for enhancing the use of Ti in numerous medical applications, particularly in dentistry.

In vitro antibacterial capacity and cytocompatibility of SiO2-CaO-P2O5 meso-macroporous glass scaffolds enriched with ZnO

Zn²⁺ ions exhibit osteogenic, angiogenic and antimicrobial properties. For this reason, they are often added in small amounts to bioceramics being investigated for bone tissue engineering. In this paper, the cytocompatibility and antibacterial properties of 80% SiO₂-15% CaO-5% P₂O₅ (mol%) mesoporous bioactive glass (MBG) scaffolds substituted with 4.0% and 7.0% of ZnO were studied and compared with the Zn-free scaffold. Cell proliferation, morphology, differentiation and cytotoxic effects of Zn²⁺ ions released from the samples were examined by culturing human osteoblast-like cells (HOS) osteoblasts both in the presence of sample extracts and on the scaffold surface. The bacterial inhibition capacity of the scaffolds was explored by using Gram-positive Stapylococcus aureus bacteria, responsible for numerous infections in orthopedic surgery, to simulate a severe infection. Our results show that the Zn-MBG scaffolds possess a hierarchical meso-macropore structure suitable for osteoblast growth. Furthermore, the amount of Zn²⁺ released from the scaffold with 4.0% ZnO was found to be more favorable for HOS cell development than that released from the scaffold including 7.0% ZnO. Zn²⁺ released to the medium from both scaffolds exhibited antibacterial properties against S. aureus. Thus, the cytocompatibility and the antibacterial ability exhibited by the MBG scaffold containing 4.0% ZnO make it a suitable candidate for bone regeneration applications.

Additivity and synergy between an antimicrobial peptide and inhibitory ions

Recently we described the pH dependence of activity for a family of cationic antimicrobial peptides (CAMPs) selected from a combinatorial library. In the current work we report on the effects of toxic ions (Cu(2+), Zn(2+), and F(-)) and the chelator EDTA on the activity profiles of one member of this family, the 12-residue cationic antimicrobial peptide *ARVA, against a panel of microorganisms. All four ions exhibited either synergy or additivity with *ARVA for all organisms tested with the exception of *ARVA combined with NaF against Candida albicans which exhibited indifference. CuCl2 and ZnCl2 exhibited synergy with *ARVA against both the Gram negative Pseudomonas aeruginosa and the Gram positive Staphylococcus aureus as well as strong additivity against Escherichia coli at submillimolar concentrations. The chelator EDTA was synergistic with *ARVA against the two Gram negative organisms but showed only simple additivity with S. aureus and C. albicans despite their much lower MICs with EDTA. This effect may be related to the known differences in the divalent ion binding properties of the Gram negative LPS layer as compared to the peptidoglycan layer of the Gram positive organism. Unlike the other ions, NaF showed only additivity or indifference when combined with *ARVA and required much higher concentrations for activity. The yeast C. albicans did not show synergy or strong additivity with any of the inhibitory compounds tested. The effects of toxic ions and chelators observed here have important implications for applications using CAMPs and for the design of novel formulations involving CAMPs. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

The bacterial adhesion on and the cytotoxicity of various dental cements used for implant-supported fixed restorations

OBJECTIVE

Bacterial adhesion on and cytotoxicity of eight luting agents used for implant-supported restorations were investigated.

MATERIALS AND METHOD

Surface roughness (Ra), surface free energy (SFE) values and three-dimensional images by atomic-force microscopy of circular specimens were determined. Bacterial suspensions of Streptococcus sanguinis and Streptococcus epidermidis were incubated at 37°C for 2 h. Adhering bacteria were examined with fluorescence dye CytoX-Violet, stained with 4',6-diamidino-2-phenylindole (DAPI) and visualized by fluorescence-microscopy. Cytotoxicity-testing was done with WST-1-tests (water soluble tetrazolium). No significant differences, neither with regard to Ra nor regarding SFE were determined.

RESULTS

Adherence of S. sanguinis was less on titanium, TempBondNE and TempBond. TempBond, TempBondNE, RelyX Unicem and Implantlink Semi Classic presented low amounts of S. epidermidis. WST-testing showed high cytotoxic potential of Harvard, Aqualox, TempBondNE and TempBond. No combination of low adherent bacteria with low cytotoxicity was found.

CONCLUSION

From a biological in-vitro perspective, none of the cements may be recommended for implant-supported restorations.

Antibacterial property expressed by a novel calcium phosphate glass

We have developed a calcium phosphate glass (CPG) doped with Zn(2+) or F(-) or combined Zn(2+) and F(-) ions, which are naturally found in the human body and play a dual role in bone formation and antibacterial activity. Previously, we have demonstrated that this family of CPGs has superior osteoconductive and resorbable properties in vivo. This study aimed to investigate the antibacterial property of CPGs incorporating Zn(2+) and/or F(-) . We used Streptococcus mutans as a model organism because it is one of the major human oral pathogens and an early colonizer, and it has been associated with several oral infections, such as dental caries, periodontitis, and peri-implantitis. CPGs of 0.01 and 0.05 g were incubated with S. mutans for 0, 2, 4, and 6 h. Serial dilutions were plated in triplicate and colony forming units were determined. The antimicrobial effect of CPG incorporating Zn(2+) or F(-) was greater than CPG incorporating both these ions. CPG without doping produced a moderate antimicrobial effect. This family of CPGs, previously shown to promote new bone formation in vivo, is demonstrated to have superior bactericidal properties.