Jonathan Lellouche

Understanding the Antibacterial Mechanism of CuO Nanoparticles: Revealing the Route of Induced Oxidative Stress

To date, there is still a lack of definite knowledge regarding the interaction of CuO nanoparticles with bacteria and the possible permeation of the nanoparticles into bacterial cells. This study was aimed at shedding light on the size-dependent (from the microscale down to the small nanoscale) antibacterial activity of CuO. The potent antibacterial activity of CuO nanoparticles was found to be due to ROS-generation by the nanoparticles attached to the bacterial cells, which in turn provoked an enhancement of the intracellular oxidative stress. This paradigm was confirmed by several assays such as lipid peroxidation and reporter strains of oxidative stress. Furthermore, electron microscopy indicated that the small nanoparticles of CuO penetrated the cells. Collectively, the results reported herein may reconcile conflicting concepts in the literature concerning the antibacterial mechanism of CuO nanoparticles, as well as highlight the potential for developing sustainable CuO nanoparticles-based devices for inhibiting bacterial infections.

Antibiofilm activity of nanosized magnesium fluoride

The ability of bacteria to develop antibiotic resistance and colonize abiotic surfaces by forming biofilms is a major cause of medical implant-associated infections and results in prolonged hospitalization periods and patient mortality. This raises the urgent need to develop compounds that can inhibit bacterial colonization of surfaces. In this study, we present an unreported microwave-based synthesis of MgF(2) nanoparticles (Nps) using ionic liquid. We demonstrate the antimicrobial activity of these fluoride nanomaterials and their ability to restrict biofilm formation of common bacterial pathogens. Scanning and transmission electron microscopic techniques indicated that the MgF(2).Nps attach and penetrate into the cells. Flow cytometry analysis revealed that the Nps caused a disruption in the membrane potential. The MgF(2).Nps also induced membrane lipid peroxidation and once internalized can interact with chromosomal DNA. Based on these findings we further explored the possibility of using the MgF(2).Nps to coat surfaces and inhibit biofilm formation. A microwave synthesis and coating procedure was utilized to coat glass coupons. The MgF(2) coated surfaces effectively restricted biofilm formation of the tested bacteria. Taken together these results highlight the potential for developing MgF(2) nanoparticles in order to inhibit bacterial infections.

ZnO nanoparticle-coated surfaces inhibit bacterial biofilm formation and increase antibiotic susceptibility

Nanotechnology is providing new ways to manipulate the structure and chemistry of surfaces to inhibit bacterial colonization. In this study, we evaluated the ability of glass slides coated with zinc oxide (ZnO) nanoparticles to restrict the biofilm formation of common bacterial pathogens. The generation of hydroxyl radicals, originating from the coated surface, was found to play a key role in antibiofilm activity. Furthermore, we evaluated the ability of the nanoparticle coating to enhance the antibacterial activity of commonly-used antibiotics. The ZnO nanoparticles were synthesized and deposited on the surface of glass slides using a one-step ultrasound irradiation process. Several physico-chemical surface characterization methods were performed to prove the long-term stability and homogenity of the coated films. Collectively, our findings may open a new door for utilizing ZnO nanoparticle films as antibiofilm coating of surfaces, thus providing a versatile platform for a wide range of applications both in medical and industrial settings, all of which are prone to bacterial colonization.

SONOCHEMICAL COATINGS OF ZNO AND CUO NANOPARTICLES INHIBIT STREPTOCOCCUS MUTANS BIOFILM FORMATION ON TEETH MODEL

Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. We recently reported on the antibiofilm activities of nanosized ZnO and CuO nanoparticles (NPs) synthesized by using sonochemical irradiation. In this study, we examined the antibacterial activity of ZnO and CuO NPs in a powder form and also examined the antibiofilm behavior of teeth surfaces that were coated with ZnO and CuO NPs using sonochemistry. Free ZnO and CuO NPs inhibited biofilm formation of Streptococcus mutans . Furthermore, by using the sonochemical procedure, we were able to coat teeth surfaces that inhibited bacterial colonization.

Antibiofilm surface functionalization of catheters by magnesium fluoride nanoparticles.

The ability of bacteria to colonize catheters is a major cause of infection. In the current study, catheters were surface-modified with MgF2 nanoparticles (NPs) using a sonochemical synthesis protocol described previously. The one-step synthesis and coating procedure yielded a homogenous MgF2 NP layer on both the inside and outside of the catheter, as analyzed by high resolution scanning electron microscopy and energy dispersive spectroscopy. The coating thickness varied from approximately 750 nm to 1000 nm on the inner walls and from approximately 450 nm to approximately 580 nm for the outer wall. The coating consisted of spherical MgF2 NPs with an average diameter of approximately 25 nm. These MgF2 NP-modified catheters were investigated for their ability to restrict bacterial biofilm formation. Two bacterial strains most commonly associated with catheter infections, Escherichia coli and Staphylococcus aureus, were cultured in tryptic soy broth, artificial urine and human plasma on the modified catheters. The MgF2 NP-coated catheters were able to significantly reduce bacterial colonization for a period of 1 week compared to the uncoated control. Finally, the potential cytotoxicity of MgF2 NPs was also evaluated using human and mammalian cell lines and no significant reduction in the mitochondrial metabolism was observed. Taken together, our results indicate that the surface modification of catheters with MgF2 NPs can be effective in preventing bacterial colonization and can provide catheters with long-lasting self-sterilizing properties.

Improved antibacterial and antibiofilm activity of magnesium fluoride nanoparticles obtained by water-based ultrasound chemistry

UNLABELLED Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. We recently reported on the antimicrobial and antibiofilm activities of nanosized magnesium fluoride (MgF(2)) nanoparticles (NPs) synthesized in ionic liquid using microwave chemistry. In this article, we describe a novel water-based synthesis of MgF(2) NPs using sonochemistry. The sonochemical irradiation of an aqueous solution of [Mg(OAc)(2)⋅(H(2)O)(4)] containing acidic HF as the fluorine ion source afforded crystalline well-shaped spherical MgF(2) NPs that showed much improved antibacterial properties against two common bacterial pathogens (Escherichia coli and Staphylococcus aureus). We were also able to demonstrate that the antimicrobial activity was dependent on the size of the NPs. In addition, using the described sonochemical process, we coated glass surfaces and demonstrated inhibition of bacterial colonization for 7 days. Finally, the antimicrobial activity of MgF(2) NPs against established biofilms was also examined. Taken together our results highlight the potential to further develop the concept of utilizing these metal fluoride NPs as novel antimicrobial and antibiofilm agents. FROM THE CLINICAL EDITOR In this article, the authors describe a novel aqueous synthesis of magnesium fluoride NPs using sonochemistry. These nanoparticles have improved antibacterial and antibiofilm activity compared to their counterparts with traditional synthesis methods.

Antibacterial and antibiofilm properties of yttrium fluoride nanoparticles

Antibiotic resistance has prompted the search for new agents that can inhibit bacterial growth. Moreover, colonization of abiotic surfaces by microorganisms and the formation of biofilms is a major cause of infections associated with medical implants, resulting in prolonged hospitalization periods and patient mortality. In this study we describe a water-based synthesis of yttrium fluoride (YF3) nanoparticles (NPs) using sonochemistry. The sonochemical irradiation of an aqueous solution of yttrium (III) acetate tetrahydrate [Y(Ac)3 · (H2O)4], containing acidic HF as the fluorine ion source, yielded nanocrystalline needle-shaped YF3 particles. The obtained NPs were characterized by scanning electron microscopy and X-ray elemental analysis. NP crystallinity was confirmed by electron and powder X-ray diffractions. YF3 NPs showed antibacterial properties against two common bacterial pathogens (Escherichia coli and Staphylococcus aureus) at a μg/mL range. We were also able to demonstrate that antimicrobial activity was dependent on NP size. In addition, catheters were surface modified with YF3 NPs using a one-step synthesis and coating process. The coating procedure yielded a homogeneous YF3 NP layer on the catheter, as analyzed by scanning electron microscopy and energy dispersive spectroscopy. These YF3 NP-modified catheters were investigated for their ability to restrict bacterial biofilm formation. The YF3 NP-coated catheters were able to significantly reduce bacterial colonization compared to the uncoated surface. Taken together, our results highlight the potential to further develop the concept of utilizing these metal fluoride NPs as novel antimicrobial and antibiofilm agents, taking advantage of their low solubility and providing extended protection.

MgF2 nanoparticle-coated teeth inhibit Streptococcus mutans biofilm formation on a tooth model

The formation of biofilms on tooth surfaces, called dental plaque, is a prerequisite for the development of both dental caries and periodontal disease. Streptococcus mutans plays an important role in the development of dental caries. Fluoride is routinely used to protect teeth against decay. In the current study, we examined whether we can use a sonochemical based method to coat artificial teeth with MgF2 nanoparticles (NPs). The results showed that the artificial tooth surface was homogenously and evenly covered with an MgF2 NP layer and successful in inhibiting S. mutans biofilm formation by over 60%. This antibiofilm activity was also present following incubation with saliva. The activity was dependent on the nano-crystalline characteristics of the material as fluoride ions could induce a similar reduction in biofilm formation. Taken together, our results indicate that the surface modification of artificial teeth with MgF2 NPs can be effective in preventing the S. mutans biofilm.

Curcumin: a natural antibiofilm agent

Biofilms resistance to killing prompts the need to discover new agents that inhibit and/or eradicate these microbial communities. Screening natural compounds for antibiofilm activity is becoming a promising approach. In this study we characterized the antibiofilm activity of curcumin. Curcumin is an extract of turmeric known to exhibit antimicrobial properties, however, its antibiofilm activity has yet to be thoroughly investigated. We find that curcumin reduces biofilm formation by Staphylococcus aureus and Escherichia coli and in addition, can effect removal and / or killing of mature biofilms. Preliminary data indicates that curcumin imposes membrane damage in S. aureus and morphological changes in E. coli cell wall which may possibly mediate the mechanism by which curcumin exerts its anti-biofilm activity. In addition, curcmin induced expression of oxidative stress related genes in E. coli, which may further imply on a possible mode of action. Our findings highlight the potential of curcumin to serve as a natural antibiofilm pharmacological agent.

Conductive hybrid carbon nanotube (CNT)–polythiophene coatings for innovative auditory neuron-multi-electrode array interfacing

Cochlear implants (CIs) are neuroprosthetic devices that restore hearing in deaf patients. They consist of a linear electrode array surgically inserted into the scala tympani of the cochlea. In this position the array directly stimulates the spiral ganglion neurons (SGNs), bypassing lost or nonfunctioning sensory hair cells. In order to reduce the energy needed to stimulate the SGNs, we attempted to improve the conductivity of the CI electrodes by creating conductive nanocomposites. We assessed the functional modification of CI platinum (Pt) pads by using multi-walled carbon nanotubes (MWCNTs) either alone or in combination with a conductive polythiophene phase, to obtain conductive nanocomposites (NCs). A novel functional poly(EDOT3:EDOT-COOH1) copolymer was synthesized by liquid-phase oxidative polymerization (LPP) of both 3,4-ethylenedioxythiophene (EDOT) and carboxylated EDOT (EDOT–COOH) monomers. Molar ratios of monomers EDOT3:EDOT-COOH1 were obtained and a poly(EDOT3:EDOT-COOH1) polymeric phase was further incorporated with oxidized MWCNTs (ox-MWCNTs) to obtain a homogeneous conductive NC phase. Immobilization of single components or NC onto Pt electrodes using cysteamine-based covalent modification has been achieved and characterized. Impedance spectroscopy of Pt-modified electrodes showed a reduced resistance at different frequencies for the specific NC consisting of poly(EDOT3:EDOT-COOH1)/SH/ox-MWCNTs/SH (1 : 1 wt%). Finally, we revealed the functional outcome of these nanostructured chemical modifications concerning the stimulation of SGN in vitro using multi-electrode arrays (MEAs). We aimed at reducing the energy needed to stimulate the SGNs and obtain an effective neuronal response. This has been observed for Pt electrodes modified with NC.