Antibiofilm and membrane-damaging potential of cuprous oxide nanoparticles against Staphylococcus aureus with reduced susceptibility to vancomycin

Silk fibroin-based coating with pH-dependent controlled release of Cu2+ for removal of implant bacterial infections

The implantation of medical devices is frequently accompanied by the invasion of bacteria, which may lead to implant failure. Therefore, an intelligent and responsive coating seems particularly essential in hindering implant-associated infections. Herein, a self-defensive antimicrobial coating, accompanied by silk fibroin as a valve, was successfully prepared on the titanium (Ti-Cu@SF) for pH-controlled release of Cu2+. The results showed that the layer could set free massive Cu2+ to strive against E. coli and S. aureus for self-defense when exposed to a slightly acidic condition. By contrary, a little Cu2+ was released in the physiological situation, which could avoid damage to the normal cells and showed excellent in vitro pH-dependent antibiosis. Besides, in vivo experiment confirmed that Ti-Cu@SF could work as an antibacterial material to kill S. aureus keenly and display negligible toxicity in vivo. Consequently, the design provided support for endowing the layer with outstanding biocompatibility and addressing the issue of bacterial infection during the implantation of Ti substrates.

Synthesis of Cu2O Nanoparticles by Ellipse Curve Micromixer

Micromixers offer the advantage of rapid and homogeneous mixing compared with conventional macroscale reaction systems, and thus they show great potential for the synthesis of nanoparticles. An ellipse curve serpentine micromixer, which had been proposed in our prior works was employed to synthesize Cu2O nanoparticles. Cu2O are excellent photocatalysts that have been widely utilized in the degradation of organic dyes. Owing to the excellent mixing performance, the reduction of Cu(OH)2 in micromixing synthesis was more sufficient than that in conventional stirring synthesis. The Cu2O nanoparticles synthesized by micromixing had smaller size and narrower size distribution compared with those synthesized by stirring in a beaker. The smallest Cu2O nanoparticles were obtained by micromixing with Re = 100 at T = 60 °C, while the most uniform Cu2O nanoparticles were obtained at T = 80 °C owing to Ostwald ripening. Through the photocatalytic degradation experiments of Rhodamine B, the Cu2O nanoparticles synthesized by micromixing were found to have better photocatalysis than those synthesized by stirring. The research results showed that the micromixing synthesis was a more suitable choice to produce Cu2O nanoparticles with excellent photocatalysis. The ellipse curve micromixer with a simple structure and high mixing performance can be applied in the synthesis of various nanoparticles.

The CuO and AgO co-modified ZnO nanocomposites for promoting wound healing in Staphylococcus aureus infection

Bacterial has become a common pathogen of humans owing to their drug-resistant effects and evasion of the host immune system, with their ability to form biofilm and induce severe infections, a condition which has become a primary public health concern globally. Herein, we report on CuO@AgO/ZnO NPs antibacterial activity enhanced by near-infrared (NIR) light which was effective in the elimination of Staphylococcus aureus and the Pseudomonas aeruginosa. The CuO@AgO/ZnO NPs under NIR significantly eradicated S. aureus and its biofilm and P. aeruginosa in vitro, and subsequently exhibited such phenomenon in vivo, eliminating bacteria and healing wound. This demonstrated the combined intrinsic antibacterial potency of the Cu and Ag components of the CuO@AgO/ZnO NPs was enhanced tremendously to achieve such outcomes in vitro and in vivo. Considering the above advantages and facile preparation methods, the CuO@AgO/ZnO NPs synthesized in this work may prove as an important antibacterial agent in bacterial-related infection therapeutics and for biomedical-related purposes.

Copper-containing nanoparticles: Mechanism of antimicrobial effect and application in dentistry-a narrative review

Copper has been used as an antimicrobial agent long time ago. Nowadays, copper-containing nanoparticles (NPs) with antimicrobial properties have been widely used in all aspects of our daily life. Copper-containing NPs may also be incorporated or coated on the surface of dental materials to inhibit oral pathogenic microorganisms. This review aims to detail copper-containing NPs' antimicrobial mechanism, cytotoxic effect and their application in dentistry.

Nanoparticles approach to eradicate bacterial biofilm-related infections: A critical review

Biofilm represents one of the crucial factors for the emergence of multi-drug resistance bacterial infections. The high mortality, morbidity and medical device-related infections are associated with biofilm formation, which requires primarily seek alternative treatment strategies. Recently, nanotechnology has emerged as a promising method for eradicating bacterial biofilm-related infection. The efficacy of nanoparticles (NPs) against bacterial infections interest great attention, and the researches on the subject are rapidly increasing. However, the majority of studies continue to focus on the antimicrobial effects of NPs in vitro, while only a few achieved in vivo and very few registered as clinical trials. The present review aimed to organize the scattered available information regarding NPs approach to eradicate bacterial biofilm-related infections. The current review highlighted the advantages and disadvantages associated with this approach, in addition to the challenges that prevent reaching the clinical applications. It was appeared that the production of NPs either as antimicrobials or as drug carriers requires further investigations to overcome the obstacles associated with their kinetic and biocompatibility.

In situ deposition of nano Cu2O on electrospun chitosan nanofibrous scaffolds and their antimicrobial properties

In order to obtain a synergistic antimicrobial effect of cuprous oxide nanoparticles (Cu₂O NPs) and chitosan (CS) nanofibers, the nano Cu₂O/CS nanofibrous scaffolds were synthesized in situ via two subsequent steps of chelation and reduction. The Cu²⁺ were stably chelated on CS nanofibrous scaffolds through the coordination of amino group (-NH₂) and hydroxyl group (-OH) on CS with Cu²⁺, and then the chelated Cu²⁺ were reduced to nano Cu₂O by Vitamin C under alkaline conditions. And by the measurements of XRD, XPS and FTIR-ATR, the results showed that Cu₂O NPs were successfully deposited on the CS nanofibrous scaffolds. SEM clarified that the particle size of Cu₂O gradually decreased and the shape changed from cubic to irregular with the increase of CuSO₄ concentration. With the CuSO₄ concentration of 0.02 and 0.04 mol·L^-1, the Cu₂O/CS nanofibrous scaffolds presented outstanding hydrophilicity and antibacterial activity against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) comparing to the CS nanofibrous scaffolds, meanwhile, they possessed good biocompatibility. This kind of nanofibrous scaffolds deposited with nano Cu₂O would have broad application prospects in the field of antibacterial biomaterials.

Identification and characterization of colistin-resistant E. coli and K. pneumoniae isolated from Lower Himalayan Region of India

Multidrug resistance is one of the worldwide public health concerns. Water represents the most suitable environment, for the exchange of antibiotic resistance genes among pathogenic to non-pathogenic bacteria. Therefore, we aimed to screen the presence of blaNDM-1, blaTEM, blaSHV, blaCTX-M and mcr1–5 genes among water samples from different locations of Lower Himachal Pradesh. We examined the genotypic incidences of blaNDM-1, blaTEM, blaSHV, blaCTXM and mcr1–5 by polymerase chain reaction. Survivability assay, fitness cost assay and biofilm assay were performed for phenotypic characterization. The presence of blaNDM-1 and its related variants were analysed and confirmed by sequencing-based approaches. A total of 73 bacterial strains were identified on M-lauryl sulphate agar medium. Out of 73 colistin-resistant isolates, 34 were E. coli and 39 were K. pneumoniae. Out of 34 samples, 2 (5.8%), 2 (5.8%), 5 (14.7%), 5 (14.7%) and 4 (11.76%) E. coli were blaTEM, blaSHV,blaCTXM-1, blaCTXM-2 and blaCTXM-15 positive, respectively. Among 39 K. pneumoniae, 15 (38.4%), 6 (15.3%), 10 (25.6%), 9 (23.07%) and 10 (25.6%) were blaTEM, blaSHV, blaCTXM-1, blaCTXM-2 and blaCTXM-15 positive, respectively. Interestingly, we observed one E. coli (HG4) isolate with both blaNDM-1 and mcr-1 gene. Further analysis showed HG4 isolate has lesser survivability on the cotton swab, long lag phase and less biofilm production compared to colistin-sensitive isolates. Detection of E. coli with blaNDM-1 and mcr-1 in this geographical region is an alarming signal for tourists, community, health workers and policymakers. Hence, it is utmost important to take appropriate measures to control the dissemination of antibiotic resistance gene in such pristine locations.

Phytofabricated silver nanoparticles: Discovery of antibacterial targets against diabetic foot ulcer derived resistant bacterial isolates

The present study selected the predominant multi antibiotic-resistant diabetic foot ulcer (DFU) derived bacterial isolates such as Pseudomonas aeruginosa (PA), Escherichia coli (EC), Staphylococcus aureus (SA) and Bacillus subtilis (BS) and evaluated their response against the well-characterized Aerva lanata (AL) reduced multiple phytochemicals fabricated silver nanoparticles (AL-AgNPs). The overnight culture of DFU isolates was processed and subjected to various studies such as antimicrobial activity, growth kinetics, biofilm disruption, reactive oxygen species (ROS), membrane leakage, membrane permeability, and damage and genotoxicity. The molecular docking of AL phytochemicals was also performed with bacterial enzyme DNA gyrase. Interestingly, AL-AgNPs were produced the remarkable antibacterial effect against the resistant DFU isolates, which was closely similar to the effect of AL-AgNPs observed against the reference strains. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of AL-AgNPs against the DFU isolates were found to be 5-15 μg/mL and 10-20 μg/mL, respectively. The AL-AgNPs were depicted a concentration-dependent growth inhibition of DFU bacterial isolates. The MIC and MBC of AL-AgNPs were effectively destroyed the preformed biofilms of DFU isolates. Furthermore, the MBC of AL-AgNPs was displayed the increased intracellular ROS accumulation, membrane leakage, permeability and damage, and genotoxicity in the DFU isolates. Additionally, the in silico study revealed that the AL phytochemicals were fitted over the binding pocket of the DNA gyrase B subunit. The observed results were confirmed that the negative impacts of the AL-AgNPs at the level of the membrane and intracellular components of DFU isolates.

Novel Antibacterial Strategies for Combating Bacterial Multidrug Resistance

BACKGROUND

Antibacterial multidrug resistance has emerged as one of the foremost global problems affecting human health. The emergence of resistant infections with the increasing number of multidrug-resistant pathogens has posed a serious problem, which required innovative collaborations across multiple disciplines to address this issue.

METHODS

In this review, we will explain the mechanisms of bacterial multidrug resistance and discuss different strategies for combating it, including combination therapy, the use of novel natural antibiotics, and the use of nanotechnology in the development of efflux pump inhibitors.

RESULTS

While combination therapy will remain the mainstay of bacterial multi-drug resistance treatment, nanotechnology will play critical roles in the development of novel treatments in the coming years.

CONCLUSION

Nanotechnology provides an encouraging platform for the development of clinically relevant and practical strategies to overcome drug resistance in the future.

Small molecule-decorated gold nanoparticles for preparing antibiofilm fabrics

The increase in antibiotic resistance reported worldwide poses an immediate threat to human health and highlights the need to find novel approaches to inhibit bacterial growth. In this study, we present a series of gold nanoparticles (Au NPs) capped by different N-heterocyclic molecules (N_Au NPs) which can serve as broad-spectrum antibacterial agents. Neither the Au NPs nor N-heterocyclic molecules were toxic to mammalian cells. These N_Au NPs can attach to the surface of bacteria and destroy the bacterial cell wall to induce cell death. Sonochemistry was used to coat Au NPs on the surface of fabrics, which showed superb antimicrobial activity against multi-drug resistant (MDR) bacteria as well as excellent efficacy in inhibiting bacterial biofilms produced by MDR bacteria. Our study provides a novel strategy for preventing the formation of MDR bacterial biofilms in a straightforward, low-cost, and efficient way, which holds promise for broad clinical applications.

Aluminium oxide nanoparticles inhibit EPS production, adhesion and biofilm formation by multidrug resistant Acinetobacter baumannii

Acinetobacter baumannii is a biofilm forming multidrug resistant (MDR) pathogen responsible for respiratory tract infections. In this study, aluminium oxide nanoparticles (Al₂O₃ NPs) were synthesized and characterized by TEM and EDX and shown to be spherical shaped nanoparticles with a diameter < 10 nm. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) for the Al₂O₃ NPs ranged between 125 and 1,000 µg ml^-1. Exposure to NPs caused cellular membrane disruption, indicated by an increase in cellular leakage of the contents. Biofilm inhibition was 11.64 to 70.2%, whereas attachment of bacteria to polystyrene surfaces was reduced to 48.8 to 51.9% in the presence of NPs. Nanoparticles also reduced extracellular polymeric substance production and the biomass of established biofilms. The data revealed the non-toxic nature of Al₂O₃ NPs up to a concentrations of 120 µg ml^-1 in HeLa cell lines. These results demonstrate an effective and safer use of Al₂O₃ NPs against the MDR A. baumannii by targeting biofilm formation, adhesion and EPS production.

One-pot fabrication of multifunctional catechin@ZIF-L nanocomposite: Assessment of antibiofilm, larvicidal and photocatalytic activities

Zeolitic imidazole framework (ZIF) is an emerging class of metal organic frameworks exhibiting unique features such as crystalline nature with tunable pore size, large surface area and biocompatible nature. Exceptional thermal and chemical stabilities of ZIF-L make it a suitable candidate for biomedical applications. The present study has focused on the single step fabrication of catechin encapsulated ZIF-L and evaluation of its antibiofilm efficiency, larvicidal activity and dye degradation ability. The as- prepared CA@ZIF-L nanocomposite was characterized by spectroscopic and microscopic techniques. The results revealed that the CA@ZIF-L showed significant toxicity against mosquito larvae in a dose dependent manner with the IC₅₀ 63.43±1.25 μg/mL. CA@ZIF-L showed dose dependent reduction of biofilm formation in both ATCC and clinical MRSA strains. In addition, CA@ZIF-L exhibited excellent photocatalytic activity with around 92% degradation of methylene blue under direct sunlight. Overall, the present work highlights the possibility of employing the multifunctional CA@ZIF-L nanocomposite as a suitable material for biomedical and photocatalytic applications.

Evaluation of antimicrobial properties of polymer nanocomposites for medical application

The paper is devoted to the investigation of antimicrobial activity of polymer nanocomposites of both low-density polyethylene and nonwoven polymeric material (a mixture of woven and polyester fibers) that had been impregnated by Cu nanoparticles. The microorganisms were grown according to generally accepted microbiological rules and on media recommended for each bacteria family. Formation of biofilms of microorganisms was studied on the surface of microtiter plates for enzyme-linked immunosorbent assay. After incubation of microtiter plates, the culture medium was removed from the wells. The wells were rinsed five times with sterile distilled water. The plates were air dried for 45 minutes and each well was stained with 1% crystal violet solution in water for 45 min. After staining, the plates were washed with sterile distilled water five times. The quantitative analysis of biofilm production was done by adding 95% ethanol for discoloration of the wells. The research shows the antibacterial activity of Cu nanoparticles on planktonic forms of the investigated microorganisms, which prevented the formation of dense biofilms. With the use of low-density polyethylene impregnated by Cu the ability to form biofilms by planktonic cells of the referent strains of microorganisms was detected to decrease by 1.7 (Escherichia coli), 12.3 (Klebsiella pneumonia) times in the studied strains and with the use of nonwoven polymeric material treated by Cu nanoparticles, the ability to form biofilms decreased by 1.8 (Escherichia coli) – 21.8 (Klebsiella pneumonia) times in the studied strains. In subjecting the formed daily biofilms of referent strains of microorganisms to Cu nanoparticles, the destruction of biofilms of the studied strains of microorganism was observed as well as violation of the integrity of the biofilm monolayer and decrease of density index in comparison with control values. As a result, the obtained polymer nanocomposites can be recommended for preventive use in the fight against nosocomial infections. The practical relevance of this study lies in the possibility of reducing the incidence of purulent-inflammatory diseases and mycoses and, accordingly, reduction of the costs of treating these diseases.

Sub lethal levels of platinum nanoparticle cures plasmid and in combination with carbapenem, curtails carbapenem resistant Escherichia coli

Drug resistance traits are rapidly disseminated across bacteria by horizontal gene transfer, especially through plasmids. Plasmid curing agents that are active both in vitro and in vivo will resensitize Multi Drug Resistant (MDR) bacteria to antimicrobial agents. Pectin capped platinum nanoparticles (PtNPs) at sub MIC (20 µM) concentration was effective, in causing loss of Extended Spectrum Beta Lactamase (ESBL) harboring plasmid as evidenced by, absence of plasmid in agarose gel and by a concomitant (16-64 fold) drop in MIC for cell wall inhibitors ceftriaxone and meropenem, in carbapenem resistant Escherichia coli (CREC). Interestingly, the plasmid cured strain exhibited small colony morphology and displayed slower growth both in vitro and in vivo. Complementation of cured strain with plasmid from the wild type strain restored resistance towards meropenem and ceftriaxone. Relative to wild type, plasmid cured strain displayed 50% reduction in biofilm formation. Plasmid curing also occurred in vivo in infected zebrafish with curing efficiency of 17% for nanoparticle + meropenem treatment. PtNPs + meropenem reduced bioburden of CREC in infected zebrafish by 2.4 log CFU. Mechanistic studies revealed that nanoparticle interacted with cell surface and perturbed inner membrane integrity. PtNPs did not induce ROS, yet it caused plasmid DNA cleavage, as evidenced by gyrase inhibition assay. Our study for the first time reveals that PtNPs as plasmid curing agent can resensitize MDR bacteria to selective antimicrobial agents in vivo.

The Green Synthesis of MgO Nano-Flowers Using Rosmarinus officinalis L. (Rosemary) and the Antibacterial Activities against Xanthomonas oryzae pv. oryzae

Recently, the use of herbs in the agriculture and food industry has increased significantly. In particular, Rosmarinus officinalis L. extracts have been reported to have strong antibacterial properties, which depend on their chemical composition. The present study displayed a biological method for synthesis of magnesium oxide (MgO) nano-flowers. The nano-flowers are developed without using any catalyst agent. Aqueous Rosemary extract was used to synthesize MgO nano-flowers (MgONFs) in stirring conditions and temperature at 70°C for 4 h. The mixture solution was checked by UV-Vis spectrum to confirm the presence of nanoparticles. The MgO nano-flowers powder was further characterized in this study by the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. In addition, bacteriological tests indicated that MgO nano-flowers significantly inhibited bacterial growth, biofilm formation, and motility of Xanthomonas oryzae pv. oryzae, which is the causal agent of bacterial blight disease in rice. The electronic microscopic observation showed that bacterial cell death may be mainly due to destroy of cell integrity, resulting in leakage of intracellular content. As recommended, the use of Rosemary extract is an effective and green way to produce the MgO nano-flowers, which can be widely used in agricultural fields to suppress bacterial infection.

Efficacy of silver nanoparticles against multidrug resistant clinical Staphylococcus aureus isolates from Nigeria

Multidrug resistant (MDR) S. aureus infections continue to account for excess mortality in hospital and community settings and constitute a rising global health problem. However, data on the efficacy and mechanism of actions of alternative solutions like silver nanoparticles in developing countries are lacking. This study investigated anti-staphylococcal activity of silver nanoparticles (AgNP) against local strains from Nigeria. A total 119 clinical isolates of S. aureus from five Nigerian laboratories categorized as MRSA (n = 52) and MSSA (n = 67) by PCR were studied. The MIC of AgNP produced by chemical reduction method and characterized by surface plasmon resonance absorbance and size equivalence by scanning electron microscopy was determined by microbroth dilution method. Its effect on protease activity and plasmids were also investigated. Baseline characteristics of the isolates revealed MDR phenotype of the isolates, carriage of diverse plasmids (15-32 kb) among the MDR MSSA, and mean extracellular protease activity of 24.8-55.7 U/mL. The chemically synthesized AgNP had a peak absorbance at 400 nm with a size equivalence of 4.58 nm. The MICs of AgNP against the isolates were 4.7 μg/mL and 4.9 μg/mL, respectively, for MRSA and MSSA (P > 0.05). The bactericidal effect of AgNP at 2.5-5 μg/mL on the MSSA and MRSA isolates was observed at 2.7-5.5 h post exposure in vitro. Further analysis revealed plasmid eviction in the MDR MSSA isolates exposed to 5 μg/mL AgNP and dose-dependent reduction in extracellular protease activity by 84.6-93.1%. Hemolysis of human erythrocytes by AgNP was not observed at the MIC range. Conclusion: This study revealed safety and efficacy of AgNP against clinical MDR S. aureus isolates from Nigeria, using plasmid eviction and protease inhibition as mechanisms of action.

Metal-Enzyme Nanoaggregates Eradicate Both Gram-Positive and Gram-Negative Bacteria and Their Biofilms

To palliate the appearance of antimicrobial resistance (AMR), the use of bactericidal agents acting differently than conventional antibiotics and the elimination of bacterial biofilm, are the two most promising strategies. Here, we integrated these two complementary strategies into new antimicrobial metal-enzyme nanoaggregates (NAs) of α-amylase and silver (αAgNAs) that are able to eliminate bacteria and their biofilm. The nanoparticle (NP) synthesis approach applied protein desolvation and laccase-mediated NP stabilization to innovatively produce catalytically active α-amylase nanoparticles (αNPs) for the elimination of the bacterial biofilm. At the same time, αNPs efficiently reduced silver for the incorporation of bactericidal Ag⁰ and formation of the αAgNAs. The bactericidal and antibiofilm efficacies of αAgNAs were demonstrated by 5.4 and 6.1 log reduction of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, respectively, and more than 80% removal of their biofilms, coupled with high biocompatibility. The biofilm-αAgNA interaction was assessed by quartz crystal microbalance and atomic force microscopy revealing how the degradation of a settled biofilm by αAgNAs caused an increase of the biofilm water content, thus weakening the biofilm surface attachment and facilitating its removal. With the present work, we not only provide a new efficient antimicrobial material to face the AMR threat, but we also envisage that the newly established method for the synthesis of metal-enzyme NAs is potentially transferable to other biocatalysts to expand the enzyme NP toolbox.

A novel bi-functional chalcone inhibits multi-drug resistant Staphylococcus aureus and potentiates the activity of fluoroquinolones

Staphylococcus aureus is the leading cause of bacteraemia and the dwindling supply of effective antibacterials has exacerbated the problem of managing infections caused by this bacterium. Isoliquiritigenin (ISL) is a plant flavonoid that displays therapeutic potential against S. aureus. The present study identified a novel mannich base derivatives of ISL, IMRG4, active against Vancomycin intermediate S. aureus (VISA). IMRG4 damages the bacterial membranes causing membrane depolarization and permeabilization, as determined by loss of salt tolerance, flow cytometric analysis, propidium idodie and fluorescent microscopy. It reduces the intracellular invasion of HEK-293 cells by S. aureus and decreases the staphylococcal load in different organs of infected mice models. In addition to anti-staphylococcal activity, IMRG4 inhibits the multidrug efflux pump, NorA, which was determined by molecular docking and EtBr efflux assays. In combination, IMRG4 significantly reduces the MIC of norfloxacin for clinical strains of S. aureus including VISA. Development of resistance against IMRG4 alone and in combination with norfloxacin was low and IMRG4 prolongs the post-antibiotic effect of norfloxacin. These virtues combined with the low toxicity of IMRG4, assessed by MTT assay and haemolysis, makes it an ideal candidate to enter drug development pipeline against S. aureus.

From Nano to Micro: using nanotechnology to combat microorganisms and their multidrug resistance

The spread of antibiotic resistance and increasing prevalence of biofilm-associated infections is driving demand for new means to treat bacterial infection. Nanotechnology provides an innovative platform for addressing this challenge, with potential to manage even infections involving multidrug-resistant (MDR) bacteria. The current review summarizes recent progress over the last 2 years in the field of antibacterial nanodrugs, and describes their unique properties, mode of action and activity against MDR bacteria and biofilms. Biocompatibility and commercialization are also discussed. As opposed to the more common division of nanoparticles (NPs) into organic- and inorganic-based materials, this review classifies NPs into two functional categories. The first includes NPs exhibiting intrinsic antibacterial properties and the second is devoted to NPs serving as a cargo for delivering antibacterial agents. Antibacterial nanomaterials used to decorate medical devices and implants are reviewed here as well.

Evaluation of anti-bacterial effects of nickel nanoparticles on biofilm production by Staphylococcus epidermidis

BACKGROUND AND OBJECTIVES

Staphylococcus epidermidis produces biofilm by extracellular polysaccharides, causing bacterial adherence to different surfaces. Anti-microbial effects of nickel nanoparticles on some bacterial strains such as S. aureus and Escherichia coli have been determined in limited studies. The aim of the present study is to examine the inhibitory effect of nickel nanoparticles on biofilm formation using clinical isolates of S. epidermidis and its hemolytic effect on human red blood cells.

MATERIALS AND METHODS

Twenty two S. epidermidis isolates were collected and identified by standard microbiological methods. Microtiter plate method was used to determine the biofilm production in bacterial isolates. The amounts of biofilm formation by isolates in the presence of 0.01, 0.05, 0.1, and 1 mg/mL concentrations of nickel nanoparticles were measured. Hemolytic activity of different concentrations of nickel nanoparticles was measured on human RBC suspensions.

RESULTS

Twenty isolates were strong, and two isolates were moderate biofilm producers. Biofilm formation significantly decreased in the presence of 0.05, 0.1, and 1 mg/mL of nickel nanoparticles (p<0.05). Although in the presence of 0.01 mg/mL of nickel nanoparticles, decrease in biofilm formation was observed but it was not statistically significant (p=0.448). Slight hemolytic activity was seen in the presence of nickel nanoparticles.

CONCLUSION

In this study, the ability of biofilm production was demonstrated for all clinical isolates of S. epidermidis. On the other hand, the lowering effects of nickel nanoparticles on biofilm formation were observed.

[Au(pyb-H)(mnt)]: A novel gold(III) 1,2-dithiolene cyclometalated complex with antimicrobial activity (pyb-H=C-deprotonated 2-benzylpyridine; mnt=1,2-dicyanoethene-1,2-dithiolate)

The novel heteroleptic cyclometalated complex [Au^III(py^b-H)(mnt)] (1; py^b-H=C-deprotonated 2-benzylpyridine; mnt =1,2-dicyanoethene-1,2-dithiolate) was tested against a panel of ten Gram positive (belonging to the Staphylococcus, Streptococcus spp. and Bacillus clausii), Gram negative (E. coli, K. pneumoniae, P. aeruginosa) bacteria and three yeasts belonging to the Candida spp. Complex 1 showed a remarkable bacteriostatic antimicrobial activity against staphylococci, with Minimum Inhibitory Concentration (MIC) values of 1.56 and 3.13μg/mL for S. haemoliticus and S. aureus, respectively. Spectroscopic and electrochemical measurements, supported by Density Functional Theory (DFT) calculations, were exploited to fully investigate the electronic structure of complex 1 and its relationship with the antimicrobial activity.