Seaweed Extracts: A Promising Source of Antibiofilm Agents with Distinct Mechanisms of Action against Pseudomonas aeruginosa.

The organization of bacteria in biofilms is one of the adaptive resistance mechanisms providing increased protection against conventional treatments. Thus, the search for new antibiofilm agents for medical purposes, especially of natural origin, is currently the object of much attention. The objective of the study presented here was to explore the potential of extracts derived from three seaweeds: the green Ulva lactuca, the brown Stypocaulon scoparium, and the red Pterocladiella capillacea, in terms of their antibiofilm activity against P. aeruginosa. After preparation of extracts by successive maceration in various solvents, their antibiofilm activity was evaluated on biofilm formation and on mature biofilms. Their inhibition and eradication abilities were determined using two complementary methods: crystal violet staining and quantification of adherent bacteria. The effect of active extracts on biofilm morphology was also investigated by epifluorescence microscopy. Results revealed a promising antibiofilm activity of two extracts (cyclohexane and ethyl acetate) derived from the green alga by exhibiting a distinct mechanism of action, which was supported by microscopic analyses. The ethyl acetate extract was further explored for its interaction with tobramycin and colistin. Interestingly, this extract showed a promising synergistic effect with tobramycin. First analyses of the chemical composition of extracts by GC-MS allowed for the identification of several molecules. Their implication in the interesting antibiofilm activity is discussed. These findings suggest the ability of the green alga U. lactuca to offer a promising source of bioactive candidates that could have both a preventive and a curative effect in the treatment of biofilms.

The healthcare costs of antimicrobial resistance in Lebanon: a multi-centre prospective cohort study from the payer perspective.

BACKGROUND: Our aim was to examine whether the length of stay, hospital charges and in-hospital mortality attributable to healthcare- and community-associated infections due to antimicrobial-resistant bacteria were higher compared with those due to susceptible bacteria in the Lebanese healthcare settings using different methodology of analysis from the payer perspective . METHODS: We performed a multi-centre prospective cohort study in ten hospitals across Lebanon. The sample size consisted of 1289 patients with documented healthcare-associated infection (HAI) or community-associated infection (CAI). We conducted three separate analysis to adjust for confounders and time-dependent bias: (1) Post-HAIs in which we included the excess LOS and hospital charges incurred after infection and (2) Matched cohort, in which we matched the patients based on propensity score estimates (3) The conventional method, in which we considered the entire hospital stay and allocated charges attributable to CAI. The linear regression models accounted for multiple confounders. RESULTS: HAIs and CAIs with resistant versus susceptible bacteria were associated with a significant excess length of hospital stay (2.69 days [95% CI,1.5-3.9]; p < 0.001) and (2.2 days [95% CI,1.2-3.3]; p < 0.001) and resulted in additional hospital charges ($1807 [95% CI, 1046-2569]; p < 0.001) and ($889 [95% CI, 378-1400]; p = 0.001) respectively. Compared with the post-HAIs analysis, the matched cohort method showed a reduction by 26 and 13% in hospital charges and LOS estimates respectively. Infections with resistant bacteria did not decrease the time to in-hospital mortality, for both healthcare- or community-associated infections. Resistant cases in the post-HAIs analysis showed a significantly higher risk of in-hospital mortality (odds ratio, 0.517 [95% CI, 0.327-0.820]; p = 0.05). CONCLUSION: This is the first nationwide study that quantifies the healthcare costs of antimicrobial resistance in Lebanon. For cases with HAIs, matched cohort analysis showed more conservative estimates compared with post-HAIs method. The differences in estimates highlight the need for a unified methodology to estimate the burden of antimicrobial resistance in order to accurately advise health policy makers and prioritize resources expenditure.

The European tiered approach for virucidal efficacy testing - rationale for rapidly selecting disinfectants against emerging and re-emerging viral diseases.

When facing an emerging virus outbreak such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a quick reaction time is key to control the spread. It takes time to develop antivirals and vaccines, and implement vaccination campaigns. Therefore, preventive measures such as rapid isolation of cases and identification and early quarantine of cases' close contacts-as well as masks, physical distancing, hand hygiene, surface disinfection and air control-are crucial to reduce the risk of transmission. In this context, disinfectants and antiseptics with proven efficacy against the outbreak virus should be used. However, biocidal formulations are quite complex and may include auxiliary substances such as surfactants or emollients in addition to active substances. In order to evaluate disinfectants' efficacy objectively, meaningful efficacy data are needed. Therefore, the European Committee for Standardisation technical committee 216 'Chemical disinfectants and antiseptics' Working Group 1 (medical area) has developed standards for efficacy testing. The European tiered approach grades the virucidal efficacy in three levels, with corresponding marker test viruses. In the case of SARS-CoV-2, disinfectants with proven activity against vaccinia virus, the marker virus for the European claim 'active against enveloped viruses', should be used to ensure effective hygiene procedures to control the pandemic.

Detection of the conformational changes of Discosoma red fluorescent proteins adhered on silver nanoparticles-based nanocomposites via surface-enhanced Raman scattering.

Description of the relationship between protein structure and function remains a primary focus in molecular biology, biochemistry, protein engineering and bioelectronics. Moreover, the investigation of the protein conformational changes after adhesion and dehydration is of importance to tackle problems related to the interaction of proteins with solid surfaces. In this paper the conformational changes of wild-type Discosoma recombinant red fluorescent proteins (DsRed) adhered on silver nanoparticles (AgNPs)-based nanocomposites are explored via surface-enhanced Raman scattering (SERS). Originality in the present approach is to work on dehydrated DsRed thin protein layers in link with natural conditions during drying. To enable the SERS effect, plasmonic substrates consisting of a single layer of AgNPs encapsulated by an ultra-thin silica cover layer were elaborated by plasma process. The achieved enhancement of the electromagnetic field in the vicinity of the AgNPs is as high as 105. This very strong enhancement factor allowed detecting Raman signals from discontinuous layers of DsRed issued from solution with protein concentration of only 80 nM. Three different conformations of the DsRed proteins after adhesion and dehydration on the plasmonic substrates were identified. It was found that the DsRed chromophore structure of the adsorbed proteins undergoes optically assisted chemical transformations when interacting with the optical beam, which leads to reversible transitions between the three different conformations. The proposed time-evolution scenario endorses the dynamical character of the relationship between protein structure and function. It also confirms that the conformational changes of proteins with strong internal coherence, like DsRed proteins, are reversible.

New insights into Legionella pneumophila biofilm regulation by c-di-GMP signaling.

The waterborne pathogen Legionella pneumophila grows as a biofilm, freely or inside amoebae. Cyclic-di-GMP (c-di-GMP), a bacterial second messenger frequently implicated in biofilm formation, is synthesized and degraded by diguanylate cyclases (DGCs) and phosphodiesterases (PDEs), respectively. To characterize the c-di-GMP-metabolizing enzymes involved in L. pneumophila biofilm regulation, the consequences on biofilm formation and the c-di-GMP concentration of each corresponding gene inactivation were assessed in the Lens strain. The results showed that one DGC and two PDEs enhance different aspects of biofilm formation, while two proteins with dual activity (DGC/PDE) inhibit biofilm growth. Surprisingly, only two mutants exhibited a change in global c-di-GMP concentration. This study highlights that specific c-di-GMP pathways control L. pneumophila biofilm formation, most likely via temporary and/or local modulation of c-di-GMP concentration. Furthermore, Lpl1054 DGC is required to enable the formation a dense biofilm in response to nitric oxide, a signal for biofilm dispersion in many other species.

Impairment of Pseudomonas aeruginosa Biofilm Resistance to Antibiotics by Combining the Drugs with a New Quorum-Sensing Inhibitor.

Pseudomonas aeruginosa plays an important role in chronic lung infections among patients with cystic fibrosis (CF) through its ability to form antibiotic-resistant biofilms. In P. aeruginosa, biofilm development and the production of several virulence factors are mainly regulated by the rhl and las quorum-sensing (QS) systems, which are controlled by two N-acyl-homoserine lactone signal molecules. In a previous study, we discovered an original QS inhibitor, N-(2-pyrimidyl)butanamide, called C11, based on the structure of C4-homoserine lactone, and found that it is able to significantly inhibit P. aeruginosa biofilm formation. However, recent data indicate that P. aeruginosa grows under anaerobic conditions and forms biofilms in the lungs of CF patients that are denser and more robust than those formed under aerobic conditions. Our confocal microscopy observations of P. aeruginosa biofilms developed under aerobic and anaerobic conditions confirmed that the biofilms formed under these two conditions have radically different architectures. C11 showed significant dose-dependent antibiofilm activity on biofilms grown under both aerobic and anaerobic conditions, with a greater inhibitory effect being seen under conditions of anaerobiosis. Gene expression analyses performed by quantitative reverse transcriptase PCR showed that C11 led to the significant downregulation of rhl QS regulatory genes but also to the downregulation of both las QS regulatory genes and QS system-regulated virulence genes, rhlA and lasB. Furthermore, the activity of C11 in combination with antibiotics against P. aeruginosa biofilms was tested, and synergistic antibiofilm activity between C11 and ciprofloxacin, tobramycin, and colistin was obtained under both aerobic and anaerobic conditions. This study demonstrates that C11 may increase the efficacy of treatments for P. aeruginosa infections by increasing the susceptibility of biofilms to antibiotics and by attenuating the pathogenicity of the bacterium.

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

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

Electrochemical assay of mammalian cell viability.

We present the first use of amperometric detection to assess the viability of mammalian cells in continuous mode, directly in the cell culture medium. Vero or HeLa cells were injected into electrochemical sensors equipped with a 3-electrode system and containing DCIP 50 µM used as the redox mediator. DCIP was reduced by the viable cells and the reduced form was detected amperometrically at 300 mV vs silver pseudo-reference. The continuous regeneration of the oxidized form of the mediator ensured a stable redox state of the cell environment, allowing the cells to survive during the measurement time. The electrochemical response was related to cell metabolism (no response with dead cells or lysed cells) and depended on both mediator concentration and cell density. The protocol was applied to both cells in suspension and adhered cells. It was also adapted to detect trans-plasma membrane electron transfer (tPMET) by replacing DCIP by ferricyanide 500 µM and using linear scan voltammetry (2 mV/s). The pioneering results described here pave the way to the development of routine electrochemical assays for cell viability and for designing a cell-based analytical platform.

Towards a better understanding of the effect of protein conditioning layers on microbial adhesion: a focused investigation of fibronectin and bovine serum albumin layers on SiO2 surfaces.

The interaction of foreign implants with their surrounding environment is significantly influenced by the adsorption of proteins on the biomaterial surfaces, playing a role in microbial adhesion. Therefore, understanding protein adsorption on solid surfaces and its effect on microbial adhesion is essential to assess the associated risk of infection. The aim of this study is to evaluate the effect of conditioning by fibronectin (Fn) or bovine serum albumin (BSA) protein layers of silica (SiO2) surfaces on the adhesion and detachment of two pathogenic microorganisms: Pseudomonas aeruginosa PAO1-Tn7-gfp and Candida albicans CIP 48.72. Experiments are conducted under both static and hydrodynamic conditions using a shear stress flow chamber. Through the use of very low wall shear stresses, the study brings the link between the static and dynamic conditions of microbial adhesion. The results reveal that the microbial adhesion critically depends on: (i) the presence of a protein layer conditioning the SiO2 surface, (ii) the type of protein and (iii) the protein conformation and organization in the conditioning layer. In addition, a very distinct adhesion behaviour of P. aeruginosa is observed towards the two tested proteins, Fn and BSA. This effect is reinforced by the amount of proteins adsorbed on the surface and their organization in the layer. The results are discussed in the light of atomic force microscopy analysis of the organization and conformation of proteins in the layers after adsorption on the SiO2 surface, as well as the specificity in bacterial behaviour when interacting with these protein layers. The study also demonstrates the very distinctive behaviours of the prokaryote P. aeruginosa PAO1-Tn7-gfp compared to the eukaryote C. albicans CIP 48.72. This underscores the importance of considering species-specific interactions between the protein conditioning layer and different pathogenic microorganisms, which appear crucial in designing tailored anti-adhesive surfaces.

Organosilylated complex [Eu(TTA)3(Bpy-Si)]: a bifunctional moiety for the engeneering of luminescent silica-based nanoparticles for bioimaging.

A new highly luminescent europium complex with the formula [Eu(TTA)3(Bpy-Si)], where TTA stands for the thenoyltrifluoroacetone, (C4H3S)COCH2COCF3, chelating ligand and Bpy-Si, Bpy-CH2NH(CH2)3Si(OEt)3, is an organosilyldipyridine ligand displaying a triethoxysilyl group as a grafting function has been synthesized and fully characterized. This bifunctional complex has been grafted onto the surface of dense silica nanoparticles (NPs) and on mesoporous silica microparticles as well. The covalent bonding of [Eu(TTA)3(Bpy-Si)] inside uniform Stöber silica nanoparticles was also achieved. The general methodology proposed could be applied to any silica matrix, allowed high grafting ratios that overcome chelate release and the tendency to agglomerate. Luminescent silica-based nanoparticles SiO2-[Eu(TTA)3(Bpy-Si)], with a diameter of 28 ± 2 nm, were successfully tested as a luminescent labels for the imaging of Pseudomonas aeruginosa biofilms. They were also functionalized by a specific monoclonal antibody and subsequently employed for the selective imaging of Escherichia coli bacteria.

Calculation of intraocular lens surface free energy and its components from contact angle measurements.

One of the most important biomaterial characteristics involved in bacterial adhesion on intraocular lenses (IOLs) is hydrophobicity. We calculated the hydrophobicity parameters of IOLs made of 6 different materials (polymethylmethacrylate, PMMA, heparin surface-modified PMMA, HSM-PMMA, silicone, hydrophilic and hydrophobic acrylics and collamer). Values of IOL surface free energy components were determined from contact angle measurements, using the Fowkes, Owens-Wendt and Good-van Oss calculations. Contact angles were higher for silicone and hydrophobic acrylic materials and lower for collamer and hydrophilic acrylic materials. The values of IOL surface free energy components obtained with the 3 different calculations were homogenous. According to the Owens-Wendt calculation, the IOLs could be separated into dispersive implants (hydrophobic acrylic, silicone and PMMA) and polar implants (collamer, hydrophilic acrylic and HSM-PMMA).

Composition and properties of silver-containing calcium carbonate-calcium phosphate bone cement.

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate-calcium phosphate (CaCO3-CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO3-CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.

Metabolic adaptation to a high-fat diet is associated with a change in the gut microbiota.

OBJECTIVE: The gut microbiota, which is considered a causal factor in metabolic diseases as shown best in animals, is under the dual influence of the host genome and nutritional environment. This study investigated whether the gut microbiota per se, aside from changes in genetic background and diet, could sign different metabolic phenotypes in mice. METHODS: The unique animal model of metabolic adaptation was used, whereby C57Bl/6 male mice fed a high-fat carbohydrate-free diet (HFD) became either diabetic (HFD diabetic, HFD-D) or resisted diabetes (HFD diabetes-resistant, HFD-DR). Pyrosequencing of the gut microbiota was carried out to profile the gut microbial community of different metabolic phenotypes. Inflammation, gut permeability, features of white adipose tissue, liver and skeletal muscle were studied. Furthermore, to modify the gut microbiota directly, an additional group of mice was given a gluco-oligosaccharide (GOS)-supplemented HFD (HFD+GOS). RESULTS: Despite the mice having the same genetic background and nutritional status, a gut microbial profile specific to each metabolic phenotype was identified. The HFD-D gut microbial profile was associated with increased gut permeability linked to increased endotoxaemia and to a dramatic increase in cell number in the stroma vascular fraction from visceral white adipose tissue. Most of the physiological characteristics of the HFD-fed mice were modulated when gut microbiota was intentionally modified by GOS dietary fibres. CONCLUSIONS: The gut microbiota is a signature of the metabolic phenotypes independent of differences in host genetic background and diet.

Direct electrochemical detection of trans-plasma membrane electron transfer: A possible alternative pathway for cell respiration.

An electrochemical protocol was designed to enable Vero cells to transfer electrons to an electrode without any added redox mediator. The cells were cultured on the surface of electrodes polarized at the optimal potential of 400 mV/silver pseudo-reference. Gold, carbon, and CNT-coated carbon electrodes displayed similar current record patterns. Extracellular electron transfer was sustained for several days. Its intensity, up to 1.5 pA.cell-1, was in the range of the electron flows implemented by cell respiration. A large fraction of the current vanished as soon as anoxic conditions were established, which suggests a mitochondrial origin for a large proportion of the electrons. The current records always showed a two-phase pattern. The occurrence of the two phases was not due to an evolution of the cell mat structure, which was fully established during the first day of polarization and did not change significantly thereafter. Increasing the cell seeding density decreased the maximum current reached during the first phase and the duration of the phase. These observations put together lead us to propose a model, in which only the cells adhered on the electrode surface produced current by metabolizing glutamine during the first phase. The possible role of this extracellular electron transfer as an alternative cell respiration pathway is discussed. The key roles it could play in regulating pH and pO2 gradients are considered, specifically to explain the pH gradient reversal observed in cancer cells. These pioneering results pave the way for electrochemical sensors to directly address cellular metabolic pathways.

Fungal Contamination of Building Materials and the Aerosolization of Particles and Toxins in Indoor Air and Their Associated Risks to Health: A Review.

It is now well established that biological pollution is a major cause of the degradation of indoor air quality. It has been shown that microbial communities from the outdoors may significantly impact the communities detected indoors. One can reasonably assume that the fungal contamination of the surfaces of building materials and their release into indoor air may also significantly impact indoor air quality. Fungi are well known as common contaminants of the indoor environment with the ability to grow on many types of building materials and to subsequently release biological particles into the indoor air. The aerosolization of allergenic compounds or mycotoxins borne by fungal particles or vehiculated by dust may have a direct impact on the occupant's health. However, to date, very few studies have investigated such an impact. The present paper reviewed the available data on indoor fungal contamination in different types of buildings with the aim of highlighting the direct connections between the growth on indoor building materials and the degradation of indoor air quality through the aerosolization of mycotoxins. Some studies showed that average airborne fungal spore concentrations were higher in buildings where mould was a contaminant than in normal buildings and that there was a strong association between fungal contamination and health problems for occupants. In addition, the most frequent fungal species on surfaces are also those most commonly identified in indoor air, regardless the geographical location in Europe or the USA. Some fungal species contaminating the indoors may be dangerous for human health as they produce mycotoxins. These contaminants, when aerosolized with fungal particles, can be inhaled and may endanger human health. However, it appears that more work is needed to characterize the direct impact of surface contamination on the airborne fungal particle concentration. In addition, fungal species growing in buildings and their known mycotoxins are different from those contaminating foods. This is why further in situ studies to identify fungal contaminants at the species level and to quantify their average concentration on both surfaces and in the air are needed to be better predict health risks due to mycotoxin aerosolization.

NaCl-induced modulation of species distribution in a mixed P. aeruginosa / S. aureus /B.cepacia biofilm.

Pseudomonas aeruginosa, Staphylococcus aureus, and Burkholderia cepacia are notorious pathogens known for their ability to form resilient biofilms, particularly within the lung environment of cystic fibrosis (CF) patients. The heightened concentration of NaCl, prevalent in the airway liquid of CF patients' lungs, has been identified as a factor that promotes the growth of osmotolerant bacteria like S. aureus and dampens host antibacterial defenses, thereby fostering favorable conditions for infections. In this study, we aimed to investigate how increased NaCl concentrations impact the development of multi-species biofilms in vitro, using both laboratory strains and clinical isolates of P. aeruginosa, S. aureus, and B. cepacia co-cultures. Employing a low-nutrient culture medium that fosters biofilm growth of the selected species, we quantified biofilm formation through a combination of adherent CFU counts, qPCR analysis, and confocal microscopy observations. Our findings reaffirmed the challenges faced by S. aureus in establishing growth within 1:1 mixed biofilms with P. aeruginosa when cultivated in a minimal medium. Intriguingly, at an elevated NaCl concentration of 145 mM, a symbiotic relationship emerged between S. aureus and P. aeruginosa, enabling their co-existence. Notably, this hyperosmotic environment also exerted an influence on the interplay of these two bacteria with B. cepacia. We demonstrated that elevated NaCl concentrations play a pivotal role in orchestrating the distribution of these three species within the biofilm matrix. Furthermore, our study unveiled the beneficial impact of NaCl on the biofilm growth of clinically relevant mucoid P. aeruginosa strains, as well as two strains of methicillin-sensitive and methicillin-resistant S. aureus. This underscores the crucial role of the microenvironment during the colonization and infection processes. The results suggest that hyperosmotic conditions could hold the key to unlocking a deeper understanding of the genesis and behavior of CF multi-species biofilms.

Discovery of potent 1,1-diarylthiogalactoside glycomimetic inhibitors of Pseudomonas aeruginosa LecA with antibiofilm properties.

In this work, ß-thiogalactoside mimetics bearing 1,1-diarylmethylene or benzophenone aglycons have been prepared and assayed for their affinity towards LecA, a lectin and virulence factor from Pseudomonas aeruginosa involved in bacterial adhesion and biofilm formation. The hit compound presents higher efficiency than previously described monovalent inhibitors and the crystal structure confirmed the occurrence of additional contacts between the aglycone and the protein surface. The highest affinity (160 nM) was obtained for a divalent ligand containing two galactosides. The monovalent high affinity compound (Kd = 1 µM) obtained through structure-activity relationship (SAR) showed efficient antibiofilm activity with no associated bactericidal activity.

Demonstrating the In Vitro and In Situ Antimicrobial Activity of Oxide Mineral Microspheres: An Innovative Technology to Be Incorporated into Porous and Nonporous Materials.

The antimicrobial activity of surfaces treated with zinc and/or magnesium mineral oxide microspheres is a patented technology that has been demonstrated in vitro against bacteria and viruses. This study aims to evaluate the efficiency and sustainability of the technology in vitro, under simulation-of-use conditions, and in situ. The tests were undertaken in vitro according to the ISO 22196:2011, ISO 20473:2013, and NF S90-700:2019 standards with adapted parameters. Simulation-of-use tests evaluated the robustness of the activity under worst-case scenarios. The in situ tests were conducted on high-touch surfaces. The in vitro results show efficient antimicrobial activity against referenced strains with a log reduction of >2. The sustainability of this effect was time-dependent and detected at lower temperatures (20 ± 2.5 °C) and humidity (46%) conditions for variable inoculum concentrations and contact times. The simulation of use proved the microsphere's efficiency under harsh mechanical and chemical tests. The in situ studies showed a higher than 90% reduction in CFU/25 cm2 per treated surface versus the untreated surfaces, reaching a targeted value of <50 CFU/cm2. Mineral oxide microspheres can be incorporated into unlimited surface types, including medical devices, to efficiently and sustainably prevent microbial contamination.

Formation of bacterial streamers during filtration in microfluidic systems.

Bacterial behavior during filtration is complex and is influenced by numerous factors. The aim of this paper is to report on experiments designed to make progress in the understanding of bacterial transfer in filters and membranes. Polydimethylsiloxane (PDMS) microsystems were built to allow direct dynamic observation of bacterial transfer across different microchannel geometries mimicking filtration processes. When filtering Escherichia coli suspensions in such devices, the bacteria accumulated in the downstream zone of the filter forming long streamers undulating in the flow. Confocal microscopy and 3D reconstruction of streamers showed how the streamers are connected to the filter and how they form in the stream. Streamer development was found to be influenced by the flow configuration and the presence of connections or tortuosity between channels. Experiments showed that streamer formation was greatest in a filtration system composed of staggered arrays of squares 10 µm apart.

The electrochemical potential is a key parameter for cell adhesion and proliferation on carbon surface.

The Nernst potential of the support/cell interface is suspected to play a key role in cell adhesion and proliferation. However, the studies that have addressed this topic have generally varied the electrochemical potential of the interface by comparing different materials or by varying the chemical composition of the surface coating. It is consequently hard to definitively separate the actual effect of the potential from possible side-effects due to differences in the surface composition or topography. Here, a 3-electrode set-up was used to apply different values of potential to identical carbon electrodes. Potentials were applied in the range -200 to 400 mV vs. silver pseudo-reference (SPR), i.e. 90 to 690 mV/SHE, to screen-printed carbon electrodes used to grow Vero or Raw 264.7 cell lines. Values up to 200 mV/SPR prohibited cell adhesion and even caused detachment of cells that were previously adhered. The value of 400 mV/DRP allowed cell adhesion and proliferation, leading to confluent and sometimes very compact mats. The zero charge potential, measured around 200 mV/DRP, showed that the drastic effect of the applied potential was probably due to the negative/positive switch of the surface charge.