Lipopolysaccharide Density and Structure Govern the Extent and Distance of Nanoparticle Interaction with Actual and Model Bacterial Outer Membranes

Quaternary Amine-Terminated Quantum Dots Induce Structural Changes to Supported Lipid Bilayers

The cytoplasmic membrane represents an essential barrier between the cytoplasm and the environment external to cells. Interaction with nanomaterials can alter the integrity of the cytoplasmic membrane through the formation of holes and membrane thinning, which can ultimately lead to adverse biological impacts. Here we use supported lipid bilayers as experimental models for the cytoplasmic membrane to investigate the impact of quantum dots functionalized with the cationic polymer poly(diallyldimethylammonium chloride) (PDDA) on membrane structure. Using a quartz crystal microbalance with dissipation monitoring we show that the positively charged quantum dots attach to and induce structural rearrangement to zwitterionic bilayers in solely the liquid-disordered phase and in those containing phase-segregated liquid-ordered domains. Real-time atomic force microscopy imaging revealed that PDDA-coated quantum dots and, to a lesser extent, PDDA itself induced the disappearance of liquid-ordered domains. We hypothesize this effect is due to an increase in energy per unit area caused by collisions between PDDA-coated quantum dots at the membrane surface. This increase in free energy per area exceeds the approximate free-energy change associated with membrane mixing between the liquid-ordered and liquid-disordered phases and results in the destabilization of membrane domains.

Peripheral Membrane Proteins Facilitate Nanoparticle Binding at Lipid Bilayer Interfaces

Molecular understanding of the impact of nanomaterials on cell membranes is critical for the prediction of effects that span environmental exposures to nanoenabled therapies. Experimental and computational studies employing phospholipid bilayers as model systems for membranes have yielded important insights but lack the biomolecular complexity of actual membranes. Here, we increase model membrane complexity by incorporating the peripheral membrane protein cytochrome c and studying the interactions of the resulting membrane systems with two types of anionic nanoparticles. Experimental and computational studies reveal that the extent of cytochrome c binding to supported lipid bilayers depends on anionic phospholipid number density and headgroup chemistry. Gold nanoparticles functionalized with short, anionic ligands or wrapped with an anionic polymer do not interact with silica-supported bilayers composed solely of phospholipids. Strikingly, when cytochrome c was bound to these bilayers, nanoparticles functionalized with short anionic ligands attached to model biomembranes in amounts proportional to the number of bound cytochrome c molecules. In contrast, anionic polymer-wrapped gold nanoparticles appeared to remove cytochrome c from supported lipid bilayers in a manner inversely proportional to the strength of cytochrome c binding to the bilayer; this reflects the removal of a weakly bound pool of cytochrome c, as suggested by molecular dynamics simulations. These results highlight the importance of the surface chemistry of both the nanoparticle and the membrane in predicting nano-bio interactions.

Antibacterial and Potentiation Properties of Charge-Optimized Polyrotaxanes for Combating Opportunistic Bacteria

Bacteria are now becoming more resistant to most conventional antibiotics. Approaches for the treatment of multidrug-resistant bacterial infections are urgently required. Cationic polymers have broad-spectrum antibacterial activity but can also induce non-specific damage to mammalian cells. Herein, we report on the design of cationic polyrotaxanes (cPRs) with variable charge densities. cPRs were prepared by conjugating neutral ethanolamine and cationic ethylenediamine at various ratios onto threaded alpha-cyclodextrins and their antimicrobial and cytocompatible properties were investigated in vitro. In contact with Gram-negative bacteria, cPRs can disrupt the bacterial outer membrane integrity via electrostatic interactions and penetrate into the cytosol. The ability of cPRs to serve as potentiators at sub-MIC concentrations, to enhance the permeability and activity of poorly permeable antibiotics such as vancomycin, erythromycin and rifampicin, was also investigated against Gram-negative P. aeruginosa PAO1 and E. coli ATCC 25922.

Probing the influence of cell surface polysaccharides on nanodendrimer binding to Gram-negative and Gram-positive bacteria using single-nanoparticle force spectroscopy

The safe use and design of nanoparticles (NPs) ask for a comprehensive interpretation of their potentially adverse effects on (micro)organisms. In this respect, the prior assessment of the interactions experienced by NPs in the vicinity of - and in contact with - complex biological surfaces is mandatory. It requires the development of suitable techniques for deciphering the processes that govern nano-bio interactions when a single organism is exposed to an extremely low dose of NPs. Here, we used atomic force spectroscopy (AFM)-based force measurements to investigate at the nanoscale the interactions between carboxylate-terminated polyamidoamine (PAMAM) nanodendrimers (radius ca. 4.5 nm) and two bacteria with very distinct surface properties, Escherichia coli and Lactococcus lactis. The zwitterionic nanodendrimers exhibit a negative peripheral surface charge and/or a positive intraparticulate core depending on the solution pH and salt concentration. Following an original strategy according to which a single dendrimer NP is grafted at the very apex of the AFM tip, the density and localization of NP binding sites are probed at the surface of E. coli and L. lactis mutants expressing different cell surface structures (presence/absence of the O-antigen of the lipopolysaccharides (LPS) or of a polysaccharide pellicle). In line with electrokinetic analysis, AFM force measurements evidence that adhesion of NPs onto pellicle-decorated L. lactis is governed by their underlying electrostatic interactions as controlled by the pH-dependent charge of the peripheral and internal NP components, and the negatively-charged cell surface. In contrast, the presence of the O-antigen on E. coli systematically suppresses the adhesion of nanodendrimers onto cells, may the apparent NP surface charge be determined by the peripheral carboxylate groups or by the internal amine functions. Altogether, this work highlights the differentiated roles played by surface polysaccharides in mediating NP attachment to Gram-positive and Gram-negative bacteria. It further demonstrates that the assessment of NP bioadhesion features requires a critical analysis of the electrostatic contributions stemming from the various structures composing the stratified cell envelope, and those originating from the bulk and surface NP components. The joint use of electrokinetics and AFM provides a valuable option for rapidly addressing the binding propensity of NPs to microorganisms, as urgently needed in NP risk assessments.

Colorimetric in situ assay of membrane-bound enzyme based on lipid bilayer inhibition of ion transport

Membrane-bound enzymes (MBEs), which make up a very high proportion of intracellular enzymes, catalyze a variety of activities that are currently analyzed by various techniques after purification. However, due to their amphipathic character, the purification of MBEs is difficult. Therefore, the most productive approach represents in situ analysis of MBEs in the cellular membrane. Methods: In this study, using membrane-bound α-glucosidase (α-Glu) as an example, we have developed a colorimetric in situ assay for MBEs based on the inhibitory effect of lipid bilayer on ion transport. The enzyme substrate could mediate the self-assembly of phospholipid PEG derivative around magnetic nanospheres that were modified with boronic acid. The formation of lipid bilayer could inhibit the leaking of iron ions under acidic conditions. However, the product of the catalytic reaction had no capability for self-assembly of the lipid bilayer, leading to the release of iron ions from the magnetic nanospheres under acidic pH. Results: The colorimetric in situ assay for MBEs could not only analyze the activity of membrane-bound α-Glu located on Caco-2 cells but could also evaluate the α-Glu inhibitors in cell medium. Conclusions: The simple, economic, and efficient method proposed here offers a potential application for high-throughput testing of α-Glu and its inhibitors. Our study also outlines a strategy for exploring the colorimetric method to detect the activities of MBEs in situ.

Hydrogen-Bond Networks near Supported Lipid Bilayers from Vibrational Sum Frequency Generation Experiments and Atomistic Simulations

We report vibrational sum frequency generation (SFG) spectra in which the C-H stretches of lipid alkyl tails in fully hydrogenated single- and dual-component supported lipid bilayers are detected along with the O-H stretching continuum above the bilayer. As the salt concentration is increased from ∼10 μM to 0.1 M, the SFG intensities in the O-H stretching region decrease by a factor of 2, consistent with significant absorptive-dispersive mixing between χ⁽²⁾ and χ⁽³⁾ contributions to the SFG signal generation process from charged interfaces. A method for estimating the surface potential from the second-order spectral lineshapes (in the OH stretching region) is presented and discussed in the context of choosing truly zero-potential reference states. Aided by atomistic simulations, we find that the strength and orientation distribution of the hydrogen bonds over the purely zwitterionic bilayers are largely invariant between submicromolar and hundreds of millimolar concentrations. However, specific interactions between water molecules and lipid headgroups are observed upon replacing phosphocholine (PC) lipids with negatively charged phosphoglycerol (PG) lipids, which coincides with SFG signal intensity reductions in the 3100-3200 cm^-1 frequency region. The atomistic simulations show that this outcome is consistent with a small, albeit statistically significant, decrease in the number of water molecules adjacent to both the lipid phosphate and choline moieties per unit area, supporting the SFG observations. Ultimately, the ability to probe hydrogen-bond networks over lipid bilayers holds the promise of opening paths for understanding, controlling, and predicting specific and nonspecific interactions between membranes and ions, small molecules, peptides, polycations, proteins, and coated and uncoated nanomaterials.

Unexpected insights into antibacterial activity of zinc oxide nanoparticles against methicillin resistant Staphylococcus aureus (MRSA)

Zinc oxide nanoparticles (ZnO-NPs) are attractive as broad-spectrum antibiotics, however, their further engineering as antimicrobial agents and clinical translation is impeded by controversial data about their mechanism of activity. It is commonly reported that ZnO-NP's antimicrobial activity is associated with the production of reactive oxygen species (ROS). Here we disprove this concept by comparing the antibacterial potency of ZnO-NPs and their capacity to generate ROS with hydrogen peroxide (H2O2). Then, using gene transcription microarray analysis, we provide evidence for a novel toxicity mechanism. Exposure to ZnO-NPs resulted in over three-log reduction in colonies of methicillin resistant S. aureus with minimal increase in ROS or lipid peroxidation. The amount of ROS required for the same amount of killing by H2O2 was much greater than that generated by ZnO-NPs. In contrast to H2O2, ZnO-NP mediated killing was not mitigated by the antioxidant, N-acetylcysteine. ZnO-NPs caused significant up-regulation of pyrimidine biosynthesis and carbohydrate degradation. Simultaneously, amino acid synthesis in S. aureus was significantly down-regulated indicating a complex mechanism of antimicrobial action involving multiple metabolic pathways. The results of this study point to the importance of specific experimental controls in the interpretation of antimicrobial mechanistic studies and the need for targeted molecular mechanism studies. Continued investigation on the antibacterial mechanisms of biomimetic ZnO-NPs is essential for future clinical translation.

Using an environmentally-relevant panel of Gram-negative bacteria to assess the toxicity of polyallylamine hydrochloride-wrapped gold nanoparticles

We aim to establish the effect of environmental diversity in evaluating nanotoxicity to bacteria. We assessed the toxicity of 4 nm polyallylamine hydrochloride-wrapped gold nanoparticles to a panel of bacteria from diverse environmental niches. The bacteria experienced a range of toxicities as evidenced by the different minimum bactericidal concentrations determined; the sensitivities of the bacteria was A. vinelandii = P. aeruginosa > S. oneidensis MR-4 > A. baylyi > S. oneidensis MR-1. Interactions between gold nanoparticles and molecular components of the cell wall were investigated by TEM, flow cytometry, and computational modeling. Binding results showed a general trend that bacteria with smooth LPS bind more PAH AuNPs than bacteria with rough LPS. Computational models reveal that PAH migrates to phosphate groups in the core of the LPS structure. Overall, our results demonstrate that simple interactions between nanoparticles and the bacterial cell wall cannot fully account for observed trends in toxicity, which points to the importance of establishing more comprehensive approaches for modeling environmental nanotoxicity.

Nanoparticle binding attenuates the pathobiology of gastric cancer-associated Helicobacter pylori

Enteric bacteria may cause severe diseases, including gastric cancer-associated Helicobacter pylori. Their infection paths overlap with the oro-gastrointestinal uptake route for nanoparticles, increasingly occurring during environmental or consumer/medical exposure. By comprehensive independent analytical methods, such as live cell fluorescence, electron as well as atomic force microscopy and elemental analysis, we show that a wide array of nanoparticles (NPs) but not microparticles form complexes with H. pylori and enteric pathogens without the need for specific functionalization. The NP-assembly that occurred rapidly was not influenced by variations in physiological temperature, though affected by the NPs' physico-chemical characteristics. Improved binding was observed for small NPs with a negative surface charge, whereas binding could be reduced by surface 'stealth' modifications. Employing human gastric epithelial cells and 3D-organoid models of the stomach, we show that NP-coating did not inhibit H. pylori's cellular attachment. However, even the assembly of non-bactericidal silica NPs attenuated H. pylori infection by reducing CagA phosphorylation, cytoskeletal rearrangement, and IL-8 secretion. Here we demonstrate that NP binding to enteric bacteria may impact their pathobiology which could be further exploited to rationally modulate the (patho)biology of microbes by nanomaterials.

Application of Nanoparticle Technologies in the Combat against Anti-Microbial Resistance

Anti-microbial resistance is a growing problem that has impacted the world and brought about the beginning of the end for the old generation of antibiotics. Increasingly, more antibiotics are being prescribed unnecessarily and this reckless practice has resulted in increased resistance towards these drugs, rendering them useless against infection. Nanotechnology presents a potential answer to anti-microbial resistance, which could stimulate innovation and create a new generation of antibiotic treatments for future medicines. Preserving existing antibiotic activity through novel formulation into or onto nanotechnologies can increase clinical longevity of action against infection. Additionally, the unique physiochemical properties of nanoparticles can provide new anti-bacterial modes of action which can also be explored. Simply concentrating on antibiotic prescribing habits will not resolve the issue but rather mitigate it. Thus, new scientific approaches through the development of novel antibiotics and formulations is required in order to employ a new generation of therapies to combat anti-microbial resistance.

Linking nanomaterial properties to biological outcomes: analytical chemistry challenges in nanotoxicology for the next decade

This article provides our perspective on the analytical challenges in nanotoxicology as the field is entering its third decade.

Single-component supported lipid bilayers probed using broadband nonlinear optics

Broadband SFG spectroscopy is shown to offer considerable advantages over scanning systems in terms of signal-to-noise ratios when probing well-formed single-component supported lipid bilayers formed from zwitterionic lipids with PC headgroups.

Bio-nano interface and environment: A critical review

The bio-nano interface is the boundary where engineered nanomaterials (ENMs) meet the biological system, exerting the biological function for which they have been designed or inducing adverse effects on other cells or organisms when they reach nontarget scenarios (i.e., the natural environment). Research has been performed to determine the fate, transport, and toxic properties of ENMs, but much of it is focused on pristine or so-called as-manufactured ENMs, or else modifications of the materials were not assessed. We review the most recent progress regarding the bio-nano interface and the transformations that ENMs undergo in the environment, paying special attention to the adsorption of environmental biomolecules on the surface of ENMs. Whereas the protein corona has received considerable attention in the fields of biomedics and human toxicology, its environmental analogue (the eco-corona) has been much less studied. A section dedicated to the analytical methods for studying and characterizing the eco-corona is also presented. We conclude by presenting and discussing the key problems and knowledge gaps that need to be resolved in the near future regarding the bio-nano interface and the eco-corona. Environ Toxicol Chem 2017;36:3181-3193. © 2017 SETAC.

Natural Organic Matter Concentration Impacts the Interaction of Functionalized Diamond Nanoparticles with Model and Actual Bacterial Membranes

Changes to nanoparticle surface charge, colloidal stability, and hydrodynamic properties induced by interaction with natural organic matter (NOM) warrant consideration in assessing the potential for these materials to adversely impact organisms in the environment. Here, we show that acquisition of a coating, or "corona", of NOM alters the hydrodynamic and electrokinetic properties of diamond nanoparticles (DNPs) functionalized with the polycation poly(allylamine HCl) in a manner that depends on the NOM-to-DNP concentration ratio. The NOM-induced changes to DNP properties alter subsequent interactions with model biological membranes and the Gram-negative bacterium Shewanella oneidensis MR-1. Suwannee River NOM induces changes to DNP hydrodynamic diameter and apparent ζ-potential in a concentration-dependent manner. At low NOM-to-DNP ratios, DNPs aggregate to a limited extent but retain a positive ζ-potential apparently due to nonuniform adsorption of NOM molecules leading to attractive electrostatic interactions between oppositely charged regions on adjacent DNP surfaces. Diamond nanoparticles at low NOM-to-DNP ratios attach to model membranes to a larger extent than in the absence of NOM (including those incorporating lipopolysaccharide, a major bacterial outer membrane component) and induce a comparable degree of membrane damage and toxicity to S. oneidensis. At higher NOM-to-DNP ratios, DNP charge is reversed, and DNP aggregates remain stable in suspension. This charge reversal eliminates DNP attachment to model membranes containing the highest LPS contents studied due to electrostatic repulsion and abolishes membrane damage to S. oneidensis. Our results demonstrate that the effects of NOM coronas on nanoparticle properties and interactions with biological surfaces can depend on the relative amounts of NOM and nanoparticles.

Nano-engineering the Antimicrobial Spectrum of Lantibiotics: Activity of Nisin against Gram Negative Bacteria

Lantibiotics, bacteria-sourced antimicrobial peptides, are very good candidates for effective and safe food additives. Among them, nisin is already approved by the EU and FDA, and has been used in food preservation for the past 40 years. Now, there is a possibility and strong interest to extend its applicability to biomedicine for designing innovative alternatives to antibiotics. The main obstacle is, however, its naturally narrow spectrum of antimicrobial activity, focused on Gram positive bacteria. Here we demonstrate broadening nisin's spectrum to Gram negative bacteria using a nano-engineering approach. After binding nisin molecules to the surface of gold nano-features, uniformly deposited on spherical carbon templates, we created a nanocomposite with a high density of positively charged groups. Before assembly, none of the components of the nanocomposite showed any activity against bacterial growth, which was changed after assembly in the form of the nanocomposite. For the first time we showed that this type of structure enables interactions capable of disintegrating the wall of Gram negative bacteria. As confirmed by the nisin model, the developed approach opens up new horizons for the use of lantibiotics in designing post-antibiotic drugs.

Cascading Effects of Nanoparticle Coatings: Surface Functionalization Dictates the Assemblage of Complexed Proteins and Subsequent Interaction with Model Cell Membranes

Interactions of functionalized nanomaterials with biological membranes are expected to be governed by not only nanoparticle physiochemical properties but also coatings or "coronas" of biomacromolecules acquired after immersion in biological fluids. Here we prepared a library of 4-5 nm gold nanoparticles (AuNPs) coated with either ω-functionalized thiols or polyelectrolyte wrappings to examine the influence of surface functional groups on the assemblage of proteins complexing the nanoparticles and its subsequent impact on attachment to model biological membranes. We find that the initial nanoparticle surface coating has a cascading effect on interactions with model cell membranes by determining the assemblage of complexing proteins, which in turn influences subsequent interaction with model biological membranes. Each type of functionalized AuNP investigated formed complexes with a unique ensemble of serum proteins that depended on the initial surface coating of the nanoparticles. Formation of protein-nanoparticle complexes altered the electrokinetic, hydrodynamic, and plasmonic properties of the AuNPs. Complexation of the nanoparticles with proteins reduced the attachment of cationic AuNPs and promoted attachment of anionic AuNPs to supported lipid bilayers; this trend is observed with both lipid bilayers comprising 100% zwitterionic phospholipids and those incorporating anionic phosphatidylinositol. Complexation with serum proteins led to attachment of otherwise noninteracting oligo(ethylene glycol)-functionalized AuNPs to bilayers containing phosphatidylinositol. These results demonstrate the importance of considering both facets of the nano-bio interface: functional groups displayed on the nanoparticle surface and proteins complexing the nanoparticles influence interaction with biological membranes as does the molecular makeup of the membranes themselves.

Probing the Interaction between Nanoparticles and Lipid Membranes by Quartz Crystal Microbalance with Dissipation Monitoring

There is increasing interest in using quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate the interaction of nanoparticles (NPs) with model surfaces. The high sensitivity, ease of use and the ability to monitor interactions in real-time has made it a popular technique for colloid chemists, biologists, bioengineers, and biophysicists. QCM-D has been recently used to probe the interaction of NPs with supported lipid bilayers (SLBs) as model cell membranes. The interaction of NPs with SLBs is highly influenced by the quality of the lipid bilayers. Unlike many surface sensitive techniques, by using QCM-D, the quality of SLBs can be assessed in real-time, hence QCM-D studies on SLB-NP interactions are less prone to the artifacts arising from bilayers that are not well formed. The ease of use and commercial availability of a wide range of sensor surfaces also have made QCM-D a versatile tool for studying NP interactions with lipid bilayers. In this review, we summarize the state-of-the-art on QCM-D based techniques for probing the interactions of NPs with lipid bilayers.

Bacteria attenuation by iron electrocoagulation governed by interactions between bacterial phosphate groups and Fe(III) precipitates

Iron electrocoagulation (Fe-EC) is a low-cost process in which Fe(II) generated from an Fe(0) anode reacts with dissolved O2 to form (1) Fe(III) precipitates with an affinity for bacterial cell walls and (2) bactericidal reactive oxidants. Previous work suggests that Fe-EC is a promising treatment option for groundwater containing arsenic and bacterial contamination. However, the mechanisms of bacteria attenuation and the impact of major groundwater ions are not well understood. In this work, using the model indicator Escherichia coli (E. coli), we show that physical removal via enmeshment in EC precipitate flocs is the primary process of bacteria attenuation in the presence of HCO3(-), which significantly inhibits inactivation, possibly due to a reduction in the lifetime of reactive oxidants. We demonstrate that the adhesion of EC precipitates to cell walls, which results in bacteria encapsulation in flocs, is driven primarily by interactions between EC precipitates and phosphate functional groups on bacteria surfaces. In single solute electrolytes, both P (0.4 mM) and Ca/Mg (1-13 mM) inhibited the adhesion of EC precipitates to bacterial cell walls, whereas Si (0.4 mM) and ionic strength (2-200 mM) did not impact E. coli attenuation. Interestingly, P (0.4 mM) did not affect E. coli attenuation in electrolytes containing Ca/Mg, consistent with bivalent cation bridging between bacterial phosphate groups and inorganic P sorbed to EC precipitates. Finally, we found that EC precipitate adhesion is largely independent of cell wall composition, consistent with comparable densities of phosphate functional groups on Gram-positive and Gram-negative cells. Our results are critical to predict the performance of Fe-EC to eliminate bacterial contaminants from waters with diverse chemical compositions.

Bacterial physiology is a key modulator of the antibacterial activity of graphene oxide

Carbon-based nanomaterials have a great potential as novel antibacterial agents; however, their interactions with bacteria are not fully understood. This study demonstrates that the antibacterial activity of graphene oxide (GO) depends on the physiological state of cells for both Gram-negative and -positive bacteria. GO susceptibility of bacteria is the highest in the exponential growth phase, which are in growing physiology, and stationary-phase (non-growing) cells are quite resistant against GO. Importantly, the order of GO susceptibility of E. coli with respect to the growth phases (exponential ≫ decline > stationary) correlates well with the changes in the envelope ultrastructures of the cells. Our findings are not only fundamentally important but also particularly critical for practical antimicrobial applications of carbon-based nanomaterials.

Evaluation of cytotoxicity, immune compatibility and antibacterial activity of biogenic silver nanoparticles

The study was focused on assessment of antibacterial activity, cytotoxicity and immune compatibility of biogenic silver nanoparticles (AgNPs) synthesized from Streptomyces sp. NH28 strain. Nanoparticles were biosynthesized and characterized by UV-Vis spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, nanoparticle tracking analysis system and zeta potential. Antibacterial activity was tested against Gram-positive and Gram-negative bacteria; minimal inhibitory concentration was recorded. Cytotoxicity was estimated using L929 mouse fibroblasts via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test. Biocompatibility of AgNPs was performed using THP1-XBlue™ cells. Biogenic AgNPs presented high antibacterial activity against all tested bacteria. Minimum inhibitory concentration of AgNPs against bacterial cells was found to be in range of 1.25-10 μg/mL. Silver nanoparticles did not show any harmful interaction to mouse fibroblast cell line, and no activation of nuclear factor kappa-light-chain-enhancer of activated B (NF-κB) cells was observed at concentration below 10 µg/mL. The half-maximal inhibitory concentration (IC₅₀) value was established at 64.5 μg/mL. Biological synthesis of silver can be used as an effective system for formation of metal nanoparticles. Biosynthesized AgNPs can be used as an antibacterial agent, which can be safe for eukaryotic cells.

Oral Challenge with Wild-Type Salmonella Typhi Induces Distinct Changes in B Cell Subsets in Individuals Who Develop Typhoid Disease

A novel human oral challenge model with wild-type Salmonella Typhi (S. Typhi) was recently established by the Oxford Vaccine Group. In this model, 104 CFU of Salmonella resulted in 65% of participants developing typhoid fever (referred here as typhoid diagnosis -TD-) 6-9 days post-challenge. TD was diagnosed in participants meeting clinical (oral temperature ≥38°C for ≥12h) and/or microbiological (S. Typhi bacteremia) endpoints. Changes in B cell subpopulations following S. Typhi challenge remain undefined. To address this issue, a subset of volunteers (6 TD and 4 who did not develop TD -NoTD-) was evaluated. Notable changes included reduction in the frequency of B cells (cells/ml) of TD volunteers during disease days and increase in plasmablasts (PB) during the recovery phase (>day 14). Additionally, a portion of PB of TD volunteers showed a significant increase in activation (CD40, CD21) and gut homing (integrin α4β7) molecules. Furthermore, all BM subsets of TD volunteers showed changes induced by S. Typhi infections such as a decrease in CD21 in switched memory (Sm) CD27+ and Sm CD27- cells as well as upregulation of CD40 in unswitched memory (Um) and Naïve cells. Furthermore, changes in the signaling profile of some BM subsets were identified after S. Typhi-LPS stimulation around time of disease. Notably, naïve cells of TD (compared to NoTD) volunteers showed a higher percentage of cells phosphorylating Akt suggesting enhanced survival of these cells. Interestingly, most these changes were temporally associated with disease onset. This is the first study to describe differences in B cell subsets directly related to clinical outcome following oral challenge with wild-type S. Typhi in humans.

A novel method developed for estimating mineralization efficiencies and its application in PC and PEC degradations of large molecule biological compounds with unknown chemical formula

A new method to estimate the photocatalytic (PC) and photoelectrocatalytic (PEC) mineralization efficiencies of large molecule biological compounds with unknown chemical formula in water was firstly developed and experimentally validated. The method employed chemical oxidation under the standard dichromate chemical oxygen demand (COD) conditions to obtain QCOD values of model compounds with unknown chemical formula. The measured QCOD values were used as the reference to replace QCOD values of model compounds for calculation of the mineralization efficiencies (in %) by assuming the obtained QCOD values are the measure of the theoretical charge required for the complete mineralization of organic pollutants. Total organic carbon (TOC) was also employed as a reference to confirm the mineralization capacity of dichromate chemical oxidation. The developed method was applied to determine the degradation extent of model compounds, such as bovine serum albumin (BSA), lecithin and bacterial DNA, by PC and PEC. Incomplete PC mineralization of all large molecule biological compounds was observed, especially for BSA. But the introduction of electrochemical technique into a PC oxidation process could profoundly improve the mineralization efficiencies of model compounds. PEC mineralization efficiencies of bacterial DNA was the highest, while that of lecithin was the lowest. Overall, PEC degradation method was found to be much effective than PC method for all large molecule biological compounds investigated, with PEC/PC mineralization ratios followed an order of BSA > lecithin > DNA.

Interactions of Bacterial Lipopolysaccharides with Gold Nanorod Surfaces Investigated by Refractometric Sensing

The interface between nanoparticles and bacterial surfaces is of great interest for applications in nanomedicine and food safety. Here, we demonstrate that interactions between gold nanorods and bacterial surface molecules are governed by the nanoparticle surface coating. Polymer-coated gold nanorod substrates are exposed to lipopolysaccharides extracted from Pseudomonas aeruginosa, Salmonella enterica and Escherichia coli, and attachment is monitored using localized surface plasmon resonance refractometric sensing. The number of lipopolysaccharide molecules attached per nanorod is calculated from the shift in the plasmon maximum, which results from the change in refractive index after analyte binding. Colloidal gold nanorods in water are also incubated with lipopolysaccharides to demonstrate the effect of lipopolysaccharide concentration on plasmon shift, ζ-potential, and association constant. Both gold nanorod surface charge and surface chemistry affect gold nanorod-lipopolysaccharide interactions. In general, anionic lipopolysaccharides was found to attach more effectively to cationic gold nanorods than to neutral or anionic gold nanorods. Some variation in lipopolysaccharide attachment is also observed between the three strains studied, demonstrating the potential complexity of bacteria-nanoparticle interactions.

Interactions of Graphene Oxide with Model Cell Membranes: Probing Nanoparticle Attachment and Lipid Bilayer Disruption

With the rapid growth in the application of graphene oxide (GO) in diverse fields, the toxicity of GO toward bacterial and mammalian cells has recently attracted extensive research attention. While several mechanisms have been proposed for the cytotoxicity of GO, the attachment of GO to cell membranes is expected to be the key initial process that precedes these mechanisms. In this study, we investigate the propensity for GO to attach to and disrupt model cell membranes using supported lipid bilayers (SLBs) and supported vesicular layers (SVLs) that are composed of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The deposition kinetics of GO on SLBs were determined using quartz crystal microbalance with dissipation monitoring and were observed to increase with increasing electrolyte (NaCl and CaCl2) concentrations, indicating that GO attachment to SLBs was controlled by electrostatic interactions. The GO deposition kinetics measured at elevated electrolyte concentrations were lower than mass-transfer-limited kinetics, likely due to the presence of hydration forces between GO and SLBs. Upon the attachment of GO to supported vesicles that were encapsulated with a fluorescent dye, dye leakage was detected, thus indicating that the lipid vesicles were disrupted. When the exposure of the SVL to the GO suspension was terminated, the leakage of dye decreased significantly, demonstrating that the pores on the lipid bilayers have a self-healing ability.