| 1. |
- Barbero, David, et al.
(författare)
-
Carbon nanotube networks : nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
- 2014
-
Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 26:19, s. 3164-
-
Tidskriftsartikel (refereegranskat)abstract
- Arrays of nano-engineered carbon nanotube networks embedded in nanoscale polymer structures enable highly efficient charge transport as demonstrated by D. R. Barbero and co-workers on page 3111. An increase in charge transport by several orders of magnitude is recorded at low nanotube loading compared to traditional random networks in either insulating (polystyrene) or semiconducting (polythiophene) polymers. These novel networks are expected to enhance the performance of next generation hybrid and carbon based photovoltaic devices.
|
|
| 2. |
- Barbero, David, et al.
(författare)
-
Nano-engineering of SWNT networks for enhanced charge transport at ultralow nanotube loading
- 2014
-
Ingår i: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 26:19, s. 3111-3117
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a simple and controllable method to form periodic arrays of highly conductive nano-engineered single wall carbon nanotube networks from solution. These networks increase the conductivity of a polymer composite by as much as eight orders of magnitude compared to a traditional random network. These nano-engineered networks are demonstrated in both polystyrene and polythiophene polymers.
|
|
| 3. |
- Barzegar, Hamid R., et al.
(författare)
-
Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter
- 2012
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:22, s. 12232-12239
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.
|
|
| 4. |
- Bielig, H, et al.
(författare)
-
NOD-like receptor activation by outer-membrane vesicles (OMVs) from non-O1 non-O139 Vibrio cholerae is modulated by the quorum sensing regulator HapR
- 2011
-
Ingår i: Infection and Immunity. - : American Society for Microbiology. - 0019-9567 .- 1098-5522. ; 79:4, s. 1418-1427
-
Tidskriftsartikel (refereegranskat)abstract
- Vibrio cholerae is an inhabitant of aquatic systems and one of the causative agents of severe dehydrating diarrhea in humans. It has also emerged as an important cause of different kinds of inflammatory responses and in particular, V. cholerae strains of the non-O1 non-O139 serogroups (NOVC) have been associated with such infections in human. We analyzed the potential of outer membrane vesicles (OMVs) derived from the NOVC strain V:5/04 to induce inflammatory responses in human host cells. V:5/04 OMVs were taken up by human epithelial cells and induced inflammatory responses. siRNA-mediated gene knock-down revealed that the inflammatory potential of NOVC OMVs was partially mediated by the nucleotide-binding domain, leucine rich repeat containing family member NOD1. Physiochemical analysis of the content of these OMVs, in conjunction with NOD1 and NOD2 reporter assays in HEK293T cells, confirmed the presence of both NOD1 and NOD2 active peptidoglycan in the OMVs. Furthermore, we show that deletion of the quorum sensing regulator HapR which mimics an infective life style, specifically reduced the inflammatory potential of the V:5/04 OMVs and their ability to activate NOD1 and NOD2. In conclusion, our study shows that NOVC OMVs elicit immune responses mediated by NOD1 and NOD2 in mammalian host cells. Moreover, we provide evidence that the quorum sensing machinery plays an important regulatory role in this process by attenuating the inflammatory potential of OMVs in infective conditions. This work thus identified a new facet of how Vibrio affects host immune responses and defines a role for the quorum sensing machinery in this process.
|
|
| 5. |
- Bjarnsholt, T., et al.
(författare)
-
Biofilm formation – what we can learn from recent developments
- 2018
-
Ingår i: Journal of Internal Medicine. - : Wiley-Blackwell. - 0954-6820 .- 1365-2796. ; 284:4, s. 332-345
-
Tidskriftsartikel (refereegranskat)abstract
- Although biofilms have been observed early in the history of microbial research, their impact has only recently been fully recognized. Biofilm infections, which contribute to up to 80% of human microbial infections, are associated with common human disorders, such as diabetes mellitus and poor dental hygiene, but also with medical implants. The associated chronic infections such as wound infections, dental caries and periodontitis significantly enhance morbidity, affect quality of life and can aid development of follow-up diseases such as cancer. Biofilm infections remain challenging to treat and antibiotic monotherapy is often insufficient, although some rediscovered traditional compounds have shown surprising efficiency. Innovative anti-biofilm strategies include application of anti-biofilm small molecules, intrinsic or external stimulation of production of reactive molecules, utilization of materials with antimicrobial properties and dispersion of biofilms by digestion of the extracellular matrix, also in combination with physical biofilm breakdown. Although basic principles of biofilm formation have been deciphered, the molecular understanding of the formation and structural organization of various types of biofilms has just begun to emerge. Basic studies of biofilm physiology have also resulted in an unexpected discovery of cyclic dinucleotide second messengers that are involved in interkingdom crosstalk via specific mammalian receptors. These findings even open up new venues for exploring novel anti-biofilm strategies.
|
|
| 6. |
|
|
| 7. |
- Cabak, Andrea, et al.
(författare)
-
Activity of airway antimicrobial peptides against cystic fibrosis pathogens
- 2020
-
Ingår i: Pathogens and Disease. - : Oxford University Press. - 2049-632X. ; 78:7
-
Tidskriftsartikel (refereegranskat)abstract
- Antimicrobial peptides are important players of the innate host defence against invading microorganisms. The aim of this study was to evaluate the activity of airway antimicrobial peptides against the common cystic fibrosis (CF) pathogen Pseudomonas aeruginosa, and to compare it to the emerging multi-drug resistant CF pathogens Achromobacter xylosoxidans and Stenotrophomonas maltophilia. Clinical bacterial isolates from CF patients were used, and the antimicrobial activity of human beta-defensin 2 and 3, LL37 and lysozyme was evaluated using radial diffusion assay and viable counts. The cell surface zeta potential was analysed to estimate the net charge at the bacterial surface. Of the bacterial species included in the study, A. xylosoxidans was the most resistant to antimicrobial peptides, whereas P. aeruginosa was the most susceptible. The net charge of the bacterial surface was significantly more negative for P. aeruginosa compared to A. xylosoxidans, which may in part explain the differences in susceptibility.
|
|
| 8. |
- Cant, David J. H., et al.
(författare)
-
Cryo-XPS for surface characterization of nanomedicines
- 2023
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:39, s. 8220-8227
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles used for medical applications commonly possess coatings or surface functionalities intended to provide specific behavior in vivo, for example, the use of PEG to provide stealth properties. Direct, quantitative measurement of the surface chemistry and composition of such systems in a hydrated environment has thus far not been demonstrated, yet such measurements are of great importance for the development of nanomedicine systems. Here we demonstrate the first use of cryo-XPS for the measurement of two PEG-functionalized nanomedicines: a polymeric drug delivery system and a lipid nanoparticle mRNA carrier. The observed differences between cryo-XPS and standard XPS measurements indicate the potential of cryo-XPS for providing quantitative measurements of such nanoparticle systems in hydrated conditions.
|
|
| 9. |
- Chung, Jade C. S., et al.
(författare)
-
Type III secretion system expression in oxygen-limited Pseudomonas aeruginosa cultures is stimulated by isocitrate lyase activity
- 2013
-
Ingår i: Open Biology. - : Royal Society of Chemistry. - 2046-2441. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- Pseudomonas aeruginosa is an opportunistic human pathogen and a common cause of chronic infections in individuals with cystic fibrosis (CF). Oxygen limitation was recently reported to regulate the expression of a major virulence determinant in P. aeruginosa, the type III secretion system (T3SS). Here, we show that expression of the T3SS in oxygen-limited growth conditions is strongly dependent on the glyoxylate shunt enzyme, isocitrate lyase (ICL; encoded by aceA), which was previously shown to be highly expressed in CF isolates. ICL-dependent regulation of the T3SS did not alter the expression level of the master transcriptional regulator, ExsA, but did affect expression of the T3 structural proteins, effectors and regulators (ExsC, ExsD and ExsE). An aceA mutant displayed enhanced biofilm formation during anaerobic growth, which suggested that AceA-dependent modulation of type III secretion might impinge upon the RetS/LadS signalling pathways. Indeed, our data suggest that RetS is able to mediate some of its effects through AceA, as expression of aceA in trans partially restored T3SS expression in a retS mutant. Our findings indicate that AceA is a key player in the metabolic regulation of T3SS expression during oxygen-limited growth of P. aeruginosa. To the best of our knowledge, this is the first demonstration that the T3SS can be regulated by factors that do not affect ExsA expression levels.
|
|
| 10. |
- Dardouri, Maïssa, et al.
(författare)
-
Assuring the Biofunctionalization of Silicone Covalently Bonded to Rhamnolipids : Antibiofilm Activity and Biocompatibility
- 2022
-
Ingår i: Pharmaceutics. - : MDPI. - 1999-4923. ; 14:9
-
Tidskriftsartikel (refereegranskat)abstract
- Silicone-based medical devices composed of polydimethylsiloxane (PDMS) are widely used all over the human body (e.g., urinary stents and catheters, central venous catheters stents) with extreme clinical success. Nevertheless, their abiotic surfaces, being prone to microorganism colonization, are often involved in infection occurrence. Improving PDMS antimicrobial properties by surface functionalization with biosurfactants to prevent related infections has been the goal of different works, but studies that mimic the clinical use of these novel surfaces are missing. This work aims at the biofunctional assessment of PDMS functionalized with rhamnolipids (RLs), using translational tests that more closely mimic the clinical microenvironment. Rhamnolipids were covalently bonded to PDMS, and the obtained surfaces were characterized by contact angle modification assessment, ATR-FTIR analysis and atomic force microscopy imaging. Moreover, a parallel flow chamber was used to assess the Staphylococcus aureus antibiofilm activity of the obtained surfaces under dynamic conditions, and an in vitro characterization with human dermal fibroblast cells in both direct and indirect characterization assays, along with an in vivo subcutaneous implantation assay in the translational rabbit model, was performed. A 1.2 log reduction in S. aureus biofilm was observed after 24 h under flow dynamic conditions. Additionally, functionalized PDMS lessened cell adhesion upon direct contact, while supporting a cytocompatible profile, within an indirect assay. The adequacy of the biological response was further validated upon in vivo subcutaneous tissue implantation. An important step was taken towards biofunctional assessment of RLs-functionalized PDMS, reinforcing their suitability for medical device usage and infection prevention.
|
|
| 11. |
- Dias, Roberta P., et al.
(författare)
-
Outer Membrane Remodeling : The Structural Dynamics and Electrostatics of Rough Lipopolysaccharide Chemotypes
- 2014
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 10:6, s. 2488-2497
-
Tidskriftsartikel (refereegranskat)abstract
- Lipopolysaccharides (LPS) are the primary constituent of the outer membrane of Gram-negative bacteria such as Pseudomonas aeruginosa. Gram-negative bacteria can synthesize modified forms of LPS in response to environmental stimuli or due to genetic mutations, a process known as outer membrane remodeling. Chemical modifications of the LPS modulate the integrity and antibiotic susceptibility of bacterial outer membranes. It also governs microbial adhesion to tissues and artificial material surfaces. We have extended a previous model of the rough LPS to include four novel chemotypes rmlC, galU, LPS Re, and Lipid-A. Atomistic molecular dynamics (MD) simulations were performed for outer membrane models constituted of each LPS chemotypes and 1,2-dipalmitoyl-3-phosphatidylethanolamine. It is shown that the decrease in the LPS polysaccharide chain length leads to a significant increase in the diffusion coefficients for the Ca2+ counterions, increase in acyl chain packing (decrease in membrane fluidity), and attenuation of the negative potential across the LPS surface as positive counterions becomes more exposed to the solvent. The electrostatic potential on the LPS surfaces reflects heterogeneous charge distributions with increasingly larger patches of positive and negative potentials as the polysaccharide chain length decreases. Such a pattern originates from the spatial arrangement of charged phosphate-Ca2+ clusters in the LPS inner-core that becomes exposed in the membrane surface as monosaccharide units are lost in the shortest chemotypes LPS Re and Lipid-A. These MD-derived conformational ensembles reproduce experimental trends and provide atom-level structural information on the rough LPS chemotypes that can help to rationalize antibiotic resistance and bacterial adhesion processes.
|
|
| 12. |
- Elbashir, Sana, 1984-, et al.
(författare)
-
Structural Study On The Chemical Environment Surrounding Phosphorus In Ash Fractions Suitable For Nutrient Recovery
- 2022
-
Ingår i: ESPC4 & PERM5 2022 – Book of Abstracts.
-
Konferensbidrag (refereegranskat)abstract
- Nutrient recovery is an integral part of sustainable clean energy production where one of the most important nutrients is phosphorus (P). Phosphorus recovery from biomass and waste ashes has been a hot topic for research and development activities for decades. However, the chemical speciation of heavy metals (HM) that may be included in recovered phosphates is yet to be resolved. Numerous trial and error approachs have been applied to lower the amount of HM content by fuel design and/or additives. Nevertheless, the connection between P and HM is theses complex phosphate systems on the atomic level is not fully understood. Therefore, exploring if HM are associated with phosphates is paramount for creating a naturallink between sustainable energy production and primary production of biomass.This study aims to examine the formation of different phosphates found in ashes and the potential inclusion of HM in their structures. The inclusion of Zn and Cu in whitlockite phosphates is investigated by powder X-ray diffraction and FTIR/RAMAN spectroscopy to identify possibilities and challenges with direct application of P-rich ash fractions as a nutrient source for plants. These measurements will be complemented by synchrotron-based X-rayabsorption spectroscopy analysis in future work.
|
|
| 13. |
- Ferreira, Magda, et al.
(författare)
-
Levofloxacin-loaded bone cement delivery system : highly effective against intracellular bacteria and Staphylococcus aureus biofilms
- 2017
-
Ingår i: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 532:1, s. 241-248
-
Tidskriftsartikel (refereegranskat)abstract
- Staphylococcus aureus is a major pathogen in bone associated infections due to its ability to adhere and form biofilms on bone and/or implants. Moreover, recrudescent and chronic infections have been associated with S. aureus capacity to invade and persist within osteoblast cells. With the growing need of novel therapeutic tools, this research aimed to evaluate some important key biological properties of a novel carrier system composed of acrylic bone cement (polymethylmethacrylate – PMMA), loaded with a release modulator (lactose) and an antibiotic (levofloxacin).Levofloxacin-loaded bone cement (BC) exhibited antimicrobial effects against planktonic and biofilm forms of S. aureus (evaluated by a flow chamber system). Moreover, novel BC formulation showed high anti-bacterial intraosteoblast activity. This fact led to the conclusion that levofloxacin released from BC matrices could penetrate the cell membrane of osteoblasts and be active against S. aureus strains in the intracellular environment. Furthermore, levofloxacin-BC formulations showed no significant in vitro cytotoxicity and no allergic potential (measured by the in vivo chorioallantoic membrane assay). Our results indicate that levofloxacin-loaded BC has potential as a local antibiotic delivery system for treating S. aureus associated bone infections.
|
|
| 14. |
- Freire, Rafael V.M., et al.
(författare)
-
Antimicrobial peptide induced colloidal transformations in bacteria-mimetic vesicles : combining in silico tools and experimental methods
- 2021
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 596, s. 352-363
-
Tidskriftsartikel (refereegranskat)abstract
- With the growing challenges of bacteria becoming resistant to conventional antibiotics, antimicrobial peptides (AMPs) may offer a potential alternative. One of the most studied AMPs, the human cathelicidin derived AMP LL-37 is notable for its antimicrobial activity even though its mechanism of action is not fully understood yet. This work investigates the interaction of LL-37 with 1-Palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (POPG) vesicles, which were employed as a bacterial membrane model given the common presence of this phospholipid in the bacterial membrane. Experimental techniques including small angle X-ray scattering, transmission electron microscopy and dynamic light scattering were used to characterize the interactions among LL-37 and POPG. Molecular dynamics simulations complement the experimental studies with molecular-level insights into the process. LL-37 was discovered to actively and critically interact with the POPG vesicles, modifying the membrane curvature that eventually leads to structural transformations from vesicles to mixed micelles. The results shed light on the mechanisms underlying the interactions among LL-37 and bacteria mimetic vesicles and can guide the further development of AMP based antimicrobial materials and therapies.
|
|
| 15. |
- Gautrot, Julien E, et al.
(författare)
-
Protein-Resistant NTA-Functionalized Polymer Brushes for Selective and Stable Immobilization of Histidine-Tagged Proteins
- 2010
-
Ingår i: Applied Materials & Interfaces. - : ACS. - 1944-8244 .- 1944-8252. ; 2:1, s. 193-202
-
Tidskriftsartikel (refereegranskat)abstract
- Protein-resistant polymeric coatings that allow highly selective immobilization of specific biomolecules are essential for biomedical applications such as microarrays, biosensing, heterogeneous catalysis, and bioengineering. Polymer brushes are particularly interesting for this purpose because their chemical structure and physical properties can easily be tailored to meet specific needs. This article explores the functionalization of two protein-resistant polymer brushes, poly(oligoethylene glycol methacrylate) (POEGMA) and poly(hydroxyethyl methacrylate) (PHEMA), with nitrilotriacetic acid (NTA) moieties that can complex histidine-tagged (His-tagged) proteins selectively and reversibly. Using fluorescence microscopy, IR spectroscopy, X-ray photoelectron spectroscopy, surface plasmon resonanace, and ellipsometry, we demonstrate that His-tagged green fluorescent protein can be immobilized on NTA brushes with high stability and loading. The loading saturation reached for NTA-POEGMA is higher than that for NTA-PHEMA because of increased swelling of the former brush. Despite this higher loading capacity, NTA-POEGMA remained highly protein-resistant, which shows its potential for “clean” and specific protein immobilization. Finally, we showed that the preserved protein resistance of NTA-POEGMA brushes can be used to generate well-defined binary biofunctional patterns via a simple protocol of incubations and washes. These patterns may find applications in cell arraying and screening.
|
|
| 16. |
- Gojkovic, Zivan, et al.
(författare)
-
Cryogenic X-ray photoelectron spectroscopy determines surface composition of algal cells and gives insights into their spontaneous sedimentation
- 2020
-
Ingår i: Algal Research. - : Elsevier. - 2211-9264. ; 47
-
Tidskriftsartikel (refereegranskat)abstract
- The flotation properties of two green microalgal species isolated from Northern Sweden, Chlorella vulgaris 13-1 and Coelastrella sp. 3-4, were investigated. C. vulgaris 13-1 is a flotating alga that remains suspended in solution during culturing, while Coelastrella sp. 3-4 is readily sedimenting in the stationary growth phase. We were the first to use cryogenic X-ray photoelectron spectroscopy (Cryo-XPS) to gain information on the chemical composition of the algal cell surface and added to these data results obtained from diffuse reflectance - Fourier Transform infrared spectroscopy (DR-FTIR) and classical chemical extractions of carbohydrates, lipids and proteins. Based on the Cryo-XPS data the surface of the sedimenting Coelastrella sp. 3-4 strain is rich in proteins and lipids, while the cell surface of non-flocculating C. vulgaris 13-1 is predominated by carbohydrates, but is poor in lipids. The Zeta-potential of both strains was equally negative. Cell size and the amount of carbohydrates on the algal cell surface, but not the negative surface charge, therefore indicate colloidal stability of microalgae in solutions and can be applied to predict flotation properties of green microalgae.
|
|
| 17. |
- Gross, Jeremy, et al.
(författare)
-
Universal soldier : Pseudomonas aeruginosa - an opportunistic generalist
- 2013
-
Ingår i: Frontiers in Biology. - : Springer. - 1674-7984 .- 1674-7992. ; 8:4, s. 387-394
-
Tidskriftsartikel (refereegranskat)abstract
- The opportunistic pathogen Pseudomonas aeruginosa commonly causes chronic and ultimately deadly lung infections in individuals with the genetic disease cystic fibrosis (CF). P. aeruginosa is metabolically diverse; it displays a remarkable ability to adapt to and successfully occupy almost any niche, including the ecologically complex CF lung. These P. aeruginosa lung infections are a fascinating example of microbial evolution within a "natural" ecosystem. Initially, P. aeruginosa shares the lung niche with a plethora of other microorganisms and is vulnerable to antibiotic challenges. Over time, adaptive evolution leads to certain commonly-observed phenotypic changes within the P. aeruginosa population, some of which render it resistant to antibiotics and apparently help it to out-compete the other species that co-habit the airways. Improving genomics techniques continue to elucidate the evolutionary mechanisms of P. aeruginosa within the CF lung and will hopefully identify new vulnerabilities in this robust and versatile pathogen. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg.
|
|
| 18. |
- Hagberg, Aleksandra, et al.
(författare)
-
Do environmental pharmaceuticals affect the composition of bacterial communities in a freshwater stream? : A case study of the Knivsta river in the south of Sweden
- 2021
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 763
-
Tidskriftsartikel (refereegranskat)abstract
- Pharmaceutical substances present at low concentrations in the environment may cause effects on biological systems such as microbial consortia living on solid riverbed substrates. These consortia are an important part of the river ecosystem as they form part of the food chain. This case study aims to contribute to an increased understanding of how low levels of pharmaceuticals in freshwater streams may influence sessile bacterial consortia. An important point source for pharmaceutical release into the environment is treated household sewage water. In order to investigate what types of effects may occur, we collected water samples as well as riverbed substrates from a small stream in the south of Sweden, Knivstaån, upstream and downstream from a sewage treatment plant (STP). Data from these samples formed the base of this case study where we investigated both the presence of pharmaceuticals in the water and bacterial composition on riverbed substrates. In the water downstream from the STP, 19 different pharmaceuticals were detected at levels below 800 ng/dm3. The microbial composition was obtained from sequencing 16S rRNA genes directly from substrates as well as from cultivated isolates. The cultivated strains showed reduced species variability compared with the data obtained directly from the substrates. No systematic differences were observed following the sampling season. However, differences could be seen between samples upstream and downstream from the STP effluent. We further observed large similarities in bacterial composition on natural stones compared to sterile stones introduced into the river approximately two months prior to sampling, giving indications for future sampling methodology of biofilms.
|
|
| 19. |
|
|
| 20. |
- Hagberg, Aleksandra, et al.
(författare)
-
Surface analysis of bacterial systems using cryo-X-ray photoelectron spectroscopy
- 2020
-
Ingår i: Surface and Interface Analysis. - : John Wiley & Sons. - 0142-2421 .- 1096-9918. ; 52, s. 792-801
-
Tidskriftsartikel (refereegranskat)abstract
- Surface analysis of biological systems using XPS often requires dehydration of the sample for it to be compatible with the ultrahigh vacuum of the spectrometer. However, if samples are frozen to liquid-nitrogen temperature prior to and during analysis, water can be retained in the sample and the organization of the sample surface should be preserved to a higher degree than in desiccated samples. This article presents recent developments of cryo-X-ray photoelectron spectroscopy (cryo-XPS) for analyses of hydrated biological samples at liquid nitrogen temperature. We describe experiments on bacterial cells, bacterial biofilms, and bacterial outer membrane vesicles using a variety of bacterial species. Differences and similarities in surface chemistry are monitored depending on growth in liquid culture, on culture plates, as well as in biofilms, and are discussed. Two data treatment methods providing decomposition of the C 1s spectra into lipid, polysaccharide, and peptide/peptidoglycan content are used and compared.
|
|
| 21. |
- Hagberg, Aleksandra, 1995-
(författare)
-
"Under pressure" : interaction between pharmaceuticals and river bacteria
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceuticals are often entering the environment without being completely decomposed. Once released in the environment they continue to carry on their main function but instead targeting the inhabitants of the aquatic ecosystem. Our interest was drawn towards the bacteria, that are often present in the environment in the form of biofilms. Despite their small size, they are carrying on important functions for the ecosystem. Any disruption in their work can potentially result a disturbance in the whole ecosystem. Thus, knowing the possible effect of the pharmaceuticals on bacterial biofilms can give us more understanding about the mechanisms that lie beneath pharmaceutical pollution.Natural degradation processes like photolysis, hydrolysis, and biodegradation can reduce pollutant concentrations. Bacterial biofilms, common in aquatic ecosystems, play a crucial role in pharmaceutical degradation process. The extracellular polymeric substances (EPS) produced by biofilms enhance their tolerance to environmental stressors.This study focuses on bacterial biofilms chronically exposed to low levels of pharmaceuticals remaining in the treated waste water released from a STP into the Knivsta River, Sweden. Using the sequencing we mapped the species that inhabited the sampling location. Model biofilm consortia were constructed and characterized using various analysis techniques. Experiments investigated bacterial motility, biofilm formation, and interactions between isolates. The bacterial isolates exhibited diverse motility patterns. Cross- cultivation assays indicated coexistence without negative interactions among isolates. Chemical analysis using ATR-FTIR spectroscopy and cryo-XPS revealed differences in macromolecular composition among isolates.The impact of pharmaceuticals, such as Trimethoprim and Diclofenac, on bacterial growth was studied.The findings contribute to understanding the complex interactions between pharmaceuticals and bacterial biofilms, crucial for assessing environmental risks and designing possible wastewater treatment strategies.
|
|
| 22. |
- Hakobyan, Shoghik, 1981-
(författare)
-
Antivirulent and antibiofilm salicylidene acylhydrazide complexes in solution and at interfaces
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing bacterial resistance against antibiotics creates a limitation for using traditional antibiotics and requests development of new approaches for treatment of bacterial infections. Among the bacterial infections that are most difficult to treat, biofilm-associated infections are one of the most hazardous. Consequently, the prevention of biofilm formation is a very important issue. One of the techniques that are widely investigated nowadays for this purpose is surface modification by polymer brushes that allows generating antifouling antibacterial surfaces. Previously, it was reported that salicylidene acylhydrazides (hydrazones) are good candidates as antivirulence drugs targeting the type three secretion system (T3SS). This secretion system is used by several Gramnegative pathogens, including Pseudomonas aeruginosa, to deliver toxins into a host cell. Furthermore, the chemical structure of these substances allows formation of complexes with metal ions, such as Fe3+ and Ga3+. The antibacterial activity of Ga3+ is well known and attributed to its similarity to the Fe3+ ion. It has also been shown that Ga3+ ions are able to suppress biofilm formation and growth in bacteria. In this thesis the chemistry of antibacterial and antivirulence Ga3+-Hydrazone complexes in solution was studied. First, to get insights in the solution chemistry, the protonation and the stability constants as well as the speciation of the Ga3+-Hydrazone complexes were determined. Additionally, a procedure for anchoring one of the hydrazone substances to antifouling polymer brushes was optimized, and the resulting surfaces were characterized. Results showed that the complexation with Ga3+ ions stabilizes the ligand and increases its solubility. Ga3+ ion binds to the hydrazone molecule forming a strong chelate that should be stable at physiological conditions. The different biological assays, such as Ga3+ uptake, antivirulence and antibiofilm effects, indicated very complex interaction of these complexes with the bacterial cell. Negatively charged and zwitterionic surfaces strongly reduced protein adsorption as well as biofilm formation. Therefore, the antifouling zwitterionic poly-[2-(methacryloyloxy)ethyl]dimethyl-3- sulfopropyl)-ammonium hydroxide (pMEDSAH) brushes were post-modified and successfully functionalized with bioactive substances via a block-copolymerization strategy. However, in order to maintain the availability of the bioactive substance after functionalization, the hydrophobic polyglycidylmethacrylate (pGMA) top block is probably better to functionalize with a lipophilic molecules to reduce diblock copolymer brush rearrangement.
|
|
| 23. |
- Hakobyan, Shoghik, et al.
(författare)
-
Functionalization of zwitterionic polymer brushes, do they remain antifouling?
- 2018
-
Ingår i: Surface and Interface Analysis. - : John Wiley & Sons. - 0142-2421 .- 1096-9918. ; 50:11, s. 1001-1006
-
Tidskriftsartikel (refereegranskat)abstract
- Polymer brushes are surface coatings that can be tailored in many ways to suit specific demands including reduction of protein and bacterial fouling of biomaterials. Previously, we reported that antifouling poly (2-(methacryloxy)ethyl)dimethyl-3-sulphopropyl ammonium hydroxide) brushes dramatically reduced formation of bacterial biofilm. We hypothesized that: (1) this brush could be efficiently functionalized with a small molecule (2-oxo-2-[N-(2,4,6-trihydroxybenzylidene)-hydrazino]-acetamide, ME0163, hydrazone) and that (2) the antifouling property would remain also after functionalization. Diblock co-polymer brushes of 2-(methacryloxy)ethyl)dimethyl-3-sulphopropyl ammonium hydroxide and poly (glycidyl methacrylate) were formed by surface-initiated atom transfer radical polymerization (SI-ATRP), and the ME0163 hydrazone was covalently bound to the surface via a ring-opening reaction. Functionalization of the surfaces was followed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis spectroscopy. The influence of temperature, reaction time, and reagent concentrations on the immobilization process was investigated. Surfaces with high degree of functionalization could be made in this way. However, the functionalization rendered the surface more hydrophobic, and the antifouling property of the brush was lost, thus, disproving the second of our starting hypotheses but corroborating the first.
|
|
| 24. |
- Hakobyan, Shoghik, et al.
(författare)
-
Influence of Chelation Strength and Bacterial Uptake of Gallium Salicylidene Acylhydrazide on Biofilm Formation and Virulence by Pseudomonas aeruginosa
- 2016
-
Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 160, s. 24-32
-
Tidskriftsartikel (refereegranskat)abstract
- Development of antibiotic resistance in bacteria causes major challenges for our society and has prompted a great need for new and alternative treatment methods for infection. One promising approach is to target bacterial virulence using for example salicylidene acylhydrazides (hydrazones). Hydrazones coordinate metal ions such as Fe(III) and Ga(III) through a five-membered and a six-membered chelation ring. One suggested mode of action is via restricting bacterial Fe uptake. Thus, it was hypothesized that the chelating strength of these substances could be used to predict their biological activity on bacterial cells. This was investigated by comparing Ga chelation strength of two hydrazone complexes, as well as bacterial Ga uptake, biofilm formation, and virulence in the form of production and secretion of a toxin (ExoS) by Pseudomonas aeruginosa. Equilibrium constants for deprotonation and Ga(III) binding of the hydrazone N′-(5-chloro-2-hydroxy-3-methylbenzylidene)-2,4-dihydroxybenzhydrazide (ME0329), with anti-virulence effect against P. aeruginosa, were determined and compared to bacterial siderophores and the previously described Ga(III) 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (Ga-ME0163) and Ga-citrate complexes. In comparison with these two complexes, it was shown that the uptake of Ga(III) was higher from the Ga-ME0329 complex. The results further show that the Ga-ME0329 complex reduced ExoS expression and secretion to a higher extent than Ga-citrate, Ga-ME0163 or the non-coordinated hydrazone. However, the effect against biofilm formation by P. aeruginosa, by the ME0329 complex, was similar to Ga-citrate and lower than what has been reported for Ga-ME0163.
|
|
| 25. |
|
|
| 26. |
- Hakobyan, Shoghik, et al.
(författare)
-
Proton and gallium(III) binding properties of a biologically active salicylidene acylhydrazide
- 2014
-
Ingår i: Journal of Inorganic Biochemistry. - : Elsevier. - 0162-0134 .- 1873-3344. ; 138, s. 9-15
-
Tidskriftsartikel (refereegranskat)abstract
- Bacterial biofilm formation causes a range of problems in our society, especially in health care. Salicylidene acylhydrazides (hydrazones) are promising antivirulence drugs targeting secretion systems used during bacterial infection of host cells. When mixed with the gallium ion they become especially potent as bacterial and biofilm growth-suppressing agents, although the mechanisms through which this occurs are not fully understood. At the base of this uncertainty lies the nature of hydrazone-metal interactions. This study addresses this issue by resolving the equilibrium speciation of hydrazone-gallium aqueous solutions. The protonation constants of the target 2-oxo-2-[N-(2,4,6-trihydroxy-benzylidene)-hydrazino]-acetamide (ME0163) hydrazone species and of its 2,4,6-trihydroxybenzaldehyde and oxamic acid hydrazide building blocks were determined by UV-visible spectrophotometry to achieve this goal. These studies show that the hydrazone is an excessively strong complexing agent for gallium and that its antivirulence properties are predominantly ascribed to monomeric 1:1Ga-ME0163 complexes of various Ga hydrolysis and ME0163 protonation states. The chelation of Ga(III) to the hydrazone also increased the stability of the compounds against acid-induced hydrolysis, making this group of compounds very interesting for biological applications where the Fe-antagonist action of both Ga(III) and the hydrazone can be combined for enhanced biological effect.
|
|
| 27. |
- Hou, Jiapeng, et al.
(författare)
-
Enhanced Antibiotic Tolerance of an In Vitro Multispecies Uropathogen Biofilm Model, Useful for Studies of Catheter-Associated Urinary Tract Infections
- 2022
-
Ingår i: Microorganisms. - : MDPI. - 2076-2607. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- Catheter-associated urinary tract infections (CAUTI) are a common clinical concern as they can lead to severe, persistent infections or bacteremia in long-term catheterized patients. This type of CAUTI is difficult to eradicate, as they are caused by multispecies biofilms that may have reduced susceptibility to antibiotics. Many new strategies to tackle CAUTI have been proposed in the past decade, including antibiotic combination treatments, surface modification and probiotic usage. However, those strategies were mainly assessed on mono- or dual-species biofilms that hardly represent the long-term CAUTI cases where, normally, 2–4 or even more species can be involved. We developed a four-species in vitro biofilm model on catheters involving clinical strains of Escherichia coli, Pseudomonas aeruginosa, Klebsiella oxytoca and Proteus mirabilis isolated from indwelling catheters. Interspecies interactions and responses to antibiotics were quantitatively assessed. Collaborative as well as competitive interactions were found among members in our model biofilm and those interactions affected the individual species’ abundances upon exposure to antibiotics as mono-, dual- or multispecies biofilms. Our study shows complex interactions between species during the assessment of CAUTI control strategies for biofilms and highlights the necessity of evaluating treatment and control regimes in a multispecies setting.
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Kapadnis, Prashant B, et al.
(författare)
-
Towards quorum-quenching catalytic antibodies
- 2009
-
Ingår i: Chemical Communications. - : RSC Publishing. - 1359-7345 .- 1364-548X. ; :5, s. 538-540
-
Tidskriftsartikel (refereegranskat)abstract
- The development of a novel method to attenuate bacterial virulence is reported, which is based upon the use of designed transition-state analogues to select human catalytic antibodies capable of degrading bacterial quorum-sensing molecules.
|
|
| 31. |
- KjÊrvik, Marit, et al.
(författare)
-
Comparative Study of NAP-XPS and Cryo-XPS for the Investigation of Surface Chemistry of the Bacterial Cell-Envelope
- 2021
-
Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Bacteria generally interact with the environment via processes involving their cell-envelope. Thus, techniques that may shed light on their surface chemistry are attractive tools for providing an understanding of bacterial interactions. One of these tools is Al Kα-excited photoelectron spectroscopy (XPS) with its estimated information depth of <10 nm. XPS-analyses of bacteria have been performed for several decades on freeze-dried specimens in order to be compatible with the vacuum in the analysis chamber of the spectrometer. A limitation of these studies has been that the freeze-drying method may collapse cell structure as well as introduce surface contaminants. However, recent developments in XPS allow for analysis of biological samples at near ambient pressure (NAP-XPS) or as frozen hydrated specimens (cryo-XPS) in vacuum. In this work, we have analyzed bacterial samples from a reference strain of the Gram-negative bacterium Pseudomonas fluorescens using both techniques. We compare the results obtained and, in general, observe good agreement between the two techniques. Furthermore, we discuss advantages and disadvantages with the two analysis approaches and the output data they provide. XPS reference data from the bacterial strain are provided, and we propose that planktonic cells of this strain (DSM 50090) are used as a reference material for surface chemical analysis of bacterial systems.
|
|
| 32. |
- Kong, Dexu, et al.
(författare)
-
Protein nanosheet mechanics controls cell adhesion and expansion on low-viscosity liquids
- 2018
-
Ingår i: Nano letters (Print). - Washington : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 18:3, s. 1946-1951
-
Tidskriftsartikel (refereegranskat)abstract
- Adherent cell culture typically requires cell spreading at the surface of solid substrates to sustain the formation of stable focal adhesions and assembly of a contractile cytoskeleton. However, a few reports have demonstrated that cell culture is possible on liquid substrates such as silicone and fluorinated oils, even displaying very low viscosities (0.77 cSt). Such behavior is surprising as low viscosity liquids are thought to relax much too fast (
|
|
| 33. |
|
|
| 34. |
- Nakao, Ryoma, et al.
(författare)
-
A highly immunogenic vaccine platform against encapsulated pathogens using chimeric probiotic Escherichia coli membrane vesicles
- 2022
-
Ingår i: npj Vaccines. - : Nature Publishing Group. - 2059-0105. ; 7:1
-
Tidskriftsartikel (refereegranskat)abstract
- Vaccines against infectious diseases should elicit potent and long-lasting immunity, ideally even in those with age-related decline in immune response. Here we report a rational polysaccharide vaccine platform using probiotic Escherichia coli-derived membrane vesicles (MVs). First, we constructed a probiotic E. coli clone harboring the genetic locus responsible for biogenesis of serotype 14 pneumococcal capsular polysaccharides (CPS14) as a model antigen. CPS14 was found to be polymerized and mainly localized on the outer membrane of the E. coli cells. The glycine-induced MVs displayed the exogenous CPS14 at high density on the outermost surface, on which the CPS14 moiety was covalently tethered to a lipid A-core oligosaccharide anchor. In in vivo immunization experiments, CPS14+MVs, but not a mixture of free CPS14 and empty MVs, strongly elicited IgG class-switch recombination with a Th1/Th2-balanced IgG subclass distribution without any adjuvant. In addition, CPS14+MVs were structurally stable with heat treatment and immunization with the heat-treated MVs-elicited CPS14-specific antibody responses in mouse serum to levels comparable to those of non-treated CPS14+MVs. Notably, the immunogenicity of CPS14+MVs was significantly stronger than those of two currently licensed vaccines against pneumococci. The CPS14+MV-elicited humoral immune responses persisted for 1 year in both blood and lung. Furthermore, the CPS14+MV vaccine was widely efficacious in mice of different ages. Even in aged mice, vaccination resulted in robust production of CPS14-specific IgG that bound to the pneumococcal cell surface. Taken together, the present probiotic E. coli MVs-based vaccine platform offers a promising, generalizable solution against encapsulated pathogens.
|
|
| 35. |
- Nakao, Ryoma, et al.
(författare)
-
Enhanced biofilm formation by Escherichia coli LPS mutants defective in hep biosynthesis
- 2012
-
Ingår i: PLOS ONE. - : Public library of science. - 1932-6203. ; 7:12, s. e51241-
-
Tidskriftsartikel (refereegranskat)abstract
- Lipopolysaccharide (LPS) is the major component of the surface of Gram-negative bacteria and its polysaccharide portion is situated at the outermost region. We investigated the relationship between the polysaccharide portion of LPS and biofilm formation using a series of Escherichia coli mutants defective in genes earlier shown to affect the LPS sugar compositions. Biofilm formation by a deep rough LPS mutant, the hldE strain, was strongly enhanced in comparison with the parental strain and other LPS mutants. The hldE strain also showed a phenotype of increased auto-aggregation and stronger cell surface hydrophobicity compared to the wild-type. Similar results were obtained with another deep rough LPS mutant, the waaC strain whose LPS showed same molecular mass as that of the hldE strain. Confocal laser scanning microscopy (CLSM) analysis and biofilm formation assay using DNase I revealed that biofilm formation by the hldE strain was dependent on extracellular DNA. Furthermore, a loss of flagella and an increase in amount of outer membrane vesicles in case of the hldE strain were also observed by transmission electron microscopy and atomic force microscopy, respectively. In addition, we demonstrated that a mutation in the hldE locus, which alters the LPS structure, caused changes in both expression and properties of several surface bacterial factors involved in biofilm formation and virulence. We suggest that the implication of these results should be considered in the context of biofilm formation on abiotic surfaces, which is frequently associated with nosocominal infections such as the catheter-associated infections.
|
|
| 36. |
- Ramstedt, Madeleine, et al.
(författare)
-
Analysis of bacterial cell surface chemical composition using cryogenic X-ray photoelectron spectroscopy
- 2016
-
Ingår i: Bacterial cell wall homeostasis. - New York, NY : Humana Press. - 9781493936762 - 9781493936748 ; , s. 215-223
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This chapter describes a method for measuring the average surface chemical composition with respect to lipids, polysaccharides, and peptides (protein + peptidoglycan) for the outer part of the bacterial cell wall. Bacterial cultures grown over night are washed with a buffer or saline at controlled pH. The analysis is done on fast-frozen bacterial cell pellets obtained after centrifugation, and the analysis requires access to X-ray photoelectron spectroscopy instrumentation that can perform analyses at cryogenic temperatures (for example using liquid nitrogen). The method can be used to monitor changes in the cell wall composition following environmental stimuli or genetic mutations. The data obtained originate from the outermost part of the cell wall. Thus, it is expected that for gram-negative bacteria only the outer membrane and part of the periplasmic peptidoglycan layer is probed during analysis, and for gram-positive bacteria only the top nanometers of the peptidoglycan layer of the cell wall is monitored.
|
|
| 37. |
- Ramstedt, Madeleine, et al.
(författare)
-
Aqueous geochemistry in the Udden pit lake, northern Sweden
- 2003
-
Ingår i: Applied Geochemistry. - 0883-2927 .- 1872-9134. ; 18:1, s. 97-108
-
Tidskriftsartikel (refereegranskat)abstract
- The Udden pit lake in northern Sweden was studied from June 1998 to February 1999 in order to increase knowledge of the geochemistry in lakes created as a result of decommissioning open pit mines. The vertical water profile in the lake was sampled on 4 different occasions, in June, August, September and February. Water samples were analysed for total concentrations of Fe, As, Cu, Cd, Zn, Pb, Al, Ca, K, Mg, Na, Mn, S, Cl, N and P. Temperature, concentration of dissolved O (sub 2) , conductivity, pH, and redox potential were measured in situ at different depths. Four layers could be observed in the lake during summer, and 3 layers during winter. A thermocline was observed during summer at a depth of 5 m and on all 4 occasions a halocline was observed at a depth of approximately 20 m, and a redoxcline at approximately 35 m. Oxygen concentration decreased dramatically at a depth of 20 m. pH increased downwards in the lake from 4.8 at the surface to 6.4 at the bottom of the lake. Geochemical processes occurring in the lake, the origins of the layers, the metal concentrations and the anion concentrations are discussed in this article
|
|
| 38. |
- Ramstedt, Madeleine, et al.
(författare)
-
Bacterial and mammalian cell response to poly(3-sulfopropyl methacrylate) brushes loaded with silver halide salts
- 2009
-
Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 30:8, s. 1524-31
-
Tidskriftsartikel (refereegranskat)abstract
- This study investigates the antibacterial and cytotoxic effect of surfaces with sulphonate brushes containing silver salts. By using the same type of samples for both cytotoxicity and antibacterial studies, these two parameters could be compared in a controlled way. The silver was incorporated into the brush in four different forms to enable release of silver ions at different concentrations and different rates. It was found that although the surfaces displayed very good antibacterial properties in buffer solutions, this effect disappeared in systems with high protein content. Similarly, the silver-containing surfaces displayed cytotoxic effects in the absence of serum proteins but this effect was reduced in the presence of serum. The speciation of silver in the different solutions is discussed. Cytotoxic and antibacterial effects are compared at the different silver concentrations released. The implications of a concentration range where silver could be used to kill bacterial without harmful effects on mammalian cells are also discussed and questioned.
|
|
| 39. |
- Ramstedt, Madeleine, et al.
(författare)
-
Bacterial surfaces in geochemistry : how can x-ray photoelectron spectroscopy help?
- 2019
-
Ingår i: Analytical geomicrobiology. - Cambridge : Cambridges Institutes Press. - 9781107070332 - 9781107707399 ; , s. 262-287
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Processes occurring at surfaces and interfaces are very important in environmental systems, necessitating surface-specific characterization tools that can help us understand processes at and specific properties of surfaces and interfaces, and their role in biogeochemical systems. This chapter describes the use and application of X-ray photoelectron spectroscopy (XPS) to study interfacial processes of relevance for geomicrobiology. Examples are given from studies determining cell wall composition, acid–base properties, cell surface charge, metal adsorption onto bacterial cells, and bacterial surface–induced precipitation of secondary minerals. As XPS is an ultrahigh-vacuum technique, several sample preparation methods have been applied to enable analysis of bacterial samples, including analysis of freeze-dried samples as well as frozen bacterial suspensions. These are described and discussed alongside advantages and disadvantages of different approaches, with a special focus on fast-freezing and the cryogenic technique.
|
|
| 40. |
- Ramstedt, Madeleine, et al.
(författare)
-
Can multi-species biofilms defeat antimicrobial surfaces on medical devices?
- 2022
-
Ingår i: Current Opinion in Biomedical Engineering. - : Elsevier. - 2468-4511. ; 22
-
Tidskriftsartikel (refereegranskat)abstract
- Infections deriving from medical devices represent a critical problem in health care causing suffering for patients, prolonged medical care, as well as consuming both human and monetary resources. An attractive solution is physical or chemical surface modifications of devices rendering them antibacterial and/or antifouling. However, the testing of such surfaces and coatings faces a range of challenges where one important is the predictability of in vitro assays for the outcome in vivo and in clinic. In this short review, we discuss what we consider is a major obstacle for design and evaluation of antimicrobial surfaces: microbial interspecies interactions. We give examples from the urinary tract, airways and from the oral cavity of functional consequences of such interactions in microbial communities, their therapeutic application for treatment, and how multi-species biofilms may influence the successful outcome of antimicrobial or antifouling surfaces. Furthermore, we suggest a path forward for in vitro testing taking these complexities into account during research and development.
|
|
| 41. |
- Ramstedt, Madeleine, et al.
(författare)
-
Cell wall composition of Bacillus subtilis changes as a function of pH and Zn2+ exposure : insights from cryo-XPS measurements
- 2014
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:15, s. 4367-4374
-
Tidskriftsartikel (refereegranskat)abstract
- Bacteria play an important role in the biogeochemical cycling of metals in the environment. Consequently, there is an interest to understand how the bacterial surfaces interact with metals in solution and how this affects the bacterial surface. In this work we have used a surface-sensitive analysis technique, cryogenic X-ray photoelectron spectroscopy (cryo-XPS), to monitor the surface of Bacillus subtilis cells as a function of pH and Zn2+ content in saline solution. The objective of the study was twofold: (1) to investigate the agreement between two data treatment methods for XPS, as well as investigate to what extent sample pretreatment may influence XPS data of bacterial samples, and (2) to characterize how the surface chemistry of bacterial cells is influenced by different external conditions. (1) It was found that the two data treatment methods gave rise to comparable results. However, identical samples analyzed fast-frozen or dry exhibited larger differences in surface chemistry, indicating that sample pretreatment can to large extents influence the obtained surface composition of bacterial samples. (2) The bacterial cell wall (in fast-frozen samples) undergoes dramatic compositional changes with pH and with Zn2+ exposure. The compositional changes are interpreted as an adaptive metal resistance response changing the biochemical composition of the bacterial cell wall. These results have implications for how adsorption processes at the surface of bacterial cells are analyzed, understood, modeled, and predicted.
|
|
| 42. |
- Ramstedt, Madeleine, et al.
(författare)
-
Characterization of hydrous manganite (-MnOOH) surfaces - an XPS study
- 2002
-
Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421. ; 34:1, s. 632-6
-
Tidskriftsartikel (refereegranskat)abstract
- Crystalline manganite (-MnOOH) has been synthesized and characterized using x-ray diffraction and high-resolution transmission electron microscopy techniques. The surface composition was studied with XPS between pH 0.4 and 11. Special pre-cooling procedures were developed to keep the manganite/water interface intact before and during XPS measurements. The O/OH group ratio differs between pH 6 and 11, in agreement with the acid/base characteristics of the surface. Below pH 6, on the other hand, drastic changes can be seen in the O 1s spectra due to dissolution of manganite. Possibly the interaction of OH groups with H+ in acidic suspensions is a first step leading to dissolution. The surface charge arising at high and low pH is compensated by the counter-ions Na+ and Cl-, respectively. The XPS spectra are presented and discussed in terms of the mechanisms for surface complexation and dissolution processes.
|
|
| 43. |
|
|
| 44. |
- Ramstedt, Madeleine, 1975-
(författare)
-
Chemical Processes at the Water-Manganite (γ-MnOOH) Interface
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemistry of mineral surfaces is of great importance in many different areas including natural processes occurring in oceans, rivers, lakes and soils. Manganese (hydr)oxides are one important group to these natural processes, and the thermodynamically most stable trivalent manganese (hydr)oxide, manganit (γ-MnOOH), is studied in this thesis. This thesis summarises six papers in which the surface chemistry of synthetic manganite has been investigated with respect to surface acid-base properties, dissolution, and adsorption of Cd(II) and the herbicide N-(phosphonomethyl)glycine (glyphosate, PMG). In these papers, a wide range of analysis techniques were used, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiometry, electrophoretic mobility measurements and wet chemical techniques, in order to obtain a more complete understanding of the different processes occurring at the manganite-water interface. From the combined use of these techniques, a 1-pKa acid-base model was established that is valid at pH>6. The model includes a Na+ interaction with the surface: =MnOH2+½ --> =MnOH-½ + H+ log β0 (intr.) = -8.20 = -pHiep =MnOH2+½ + Na+ --> =MnOHNa+½ + H+ log β0 (intr.) = -9.64 At pH<6 the manganite crystals dissolve and disproportionate into pyrolusite (β-MnO2) and Mn(II)-ions in solution according to: 2 γ-MnOOH + 2H+ --> β-MnO2 + Mn2+ + 2H2O log K0 = 7.61 ± 0.10 The adsorption and co-adsorption of Cd(II) and glyphosate at the manganite surface was studied at pH>6. Cd(II) adsorption displays an adsorption edge at pH~8.5. Glyphosate adsorbs over the entire pH range, but the adsorption decreases with increasing pH. When the two substances are co-adsorbed, the adsorption of Cd(II) is increased at low pH but decreased at high pH. The adsorption of glyphosate is increased in the entire pH range in the presence of Cd(II). From XPS, FTIR and EXAFS it was found that glyphosate and Cd(II) form inner sphere complexes. The binary Cd(II)-surface complex is bonded by edge sharing of Mn and Cd octahedra on the (010) plane of manganite. Glyphosate forms inner-sphere complexes through an interaction between the phosphonate group and the manganite surface. The largest fraction of this binary glyphosate complex is protonated throughout the pH range. A ternary surface complex is also present, and its structure is explained as type B ternary surface complex (surface-glyphosate-Cd(II)). The chelating rings between the Cd(II) and glyphosate, found in aqueous complexes, are maintained at the surface, and the ternary complex is bound to the surface through the phosphonate group of the ligand.
|
|
| 45. |
- Ramstedt, Madeleine, et al.
(författare)
-
Chemical speciation of N-(phosphonomethyl)glycine in solution and at mineral interfaces
- 2004
-
Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 36:8, s. 1074-7
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical speciation of the zwitterionic compound N-(phosphonomethyl)glycine (PMG) was studied in solution and at the mineral/water interface at different pH. Results from vacuum techniques such as XPS were compared with previously published conventional batch experiments. It was shown that by keeping the samples frozen during XPS analyses it was possible to keep a water interface. The frozen interface enables studies of the protonation of the nitrogen group which has previously been difficult using XPS. The protonation in frozen solutions was compared with literature data and the differences discussed. Furthermore, the speciation of PMG at the surface of manganite (-MnOOH) and goethite (-FeOOH) was studied. It was found that at least one of the protonation constants for surface-bound PMG differs significantly from the protonation constants in a pure PMG solution. The formation of different surface complexes is discussed together with differences between the sorption capacities of PMG onto the minerals studied.
|
|
| 46. |
- Ramstedt, Madeleine, et al.
(författare)
-
Co-adsorption of cadmium(II) and glyphosate at the water–manganite (γ-MnOOH) interface
- 2005
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 285:2, s. 493-501
-
Tidskriftsartikel (refereegranskat)abstract
- The co-adsorption of Cd(II) and glyphosate (N-(phosphonomethyl)glycine, PMG) at the manganite (γ-MnOOH) surface has been studied in the pH range 6–10 at 25 °C and with 0.1 M Na(Cl) as ionic medium. Batch adsorption experiments, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used for the quantitative analysis and the determination of the molecular structure of the surface complexes. The adsorption of Cd(II) and PMG in the ternary Cd(II)–PMG–manganite system was compared with the adsorption in the binary Cd(II)–manganite and PMG–manganite systems. The formation of three inner sphere surface complexes was observed, a ternary Cd(II)–PMG–manganite complex, a binary Cd(II)–manganite complex and a binary PMG–manganite complex. The surface concentration of the ternary complex and the Cd(II)–manganite complex was more or less constant throughout the pH range studied. However, the surface concentration of the binary PMG–manganite complex decreased with increasing pH. The major part of the binary PMG–surface complex was protonated. The ternary surface complex displayed a type B structure (Cd(II)–PMG–manganite). The average Cd–Mn distance obtained from EXAFS (3.26 Å) indicates that the binary and ternary Cd(II)–surface complexes are formed by edge-sharing of Mn and Cd octahedra on the (010) plane of the manganite crystals.
|
|
| 47. |
- Ramstedt, Madeleine, et al.
(författare)
-
Cryo-XPS spectra from bacterial reference strain Pseudomonas fluorescens DSM50090
- 2022
-
Ingår i: Surface Science Spectra. - : AVS Science and Technology Society. - 1055-5269 .- 1520-8575. ; 29:1
-
Tidskriftsartikel (refereegranskat)abstract
- Cryogenic x-ray photoelectron spectroscopy was used to analyze the cell envelope of intact and hydrated Gram-negative bacteria of the species Pseudomonas fluorescens. We used a reference strain, DSM50090, from the German microbial culture collection, which we previously have suggested would function well as a reference strain for future XPS analyses of Gram-negative bacteria. Bacteria were grown on nutrient agar plates at room temperature, collected with a cultivation loop, and washed using phosphate buffered saline. An aliquot of the cell pellet was fast-frozen on the sample holder in the sample introduction chamber to a temperature of 103 K and kept frozen throughout the measurement. Survey spectra and high-resolution spectra of Na 1s, O 1s, N 1s, C 1s, Cl 2p, S 2p, and P 2p are reported. The spectra obtained from the analyzed cells represent a combined signal from O, N, C, and S atoms in proteins, lipids, and polysaccharides at the cell surface. Furthermore, signal from P, Na, K, and Cl atoms was present both originating from processes in the cell envelope and remnants from the wash buffer.
|
|
| 48. |
- Ramstedt, Madeleine, et al.
(författare)
-
Difficulties in determining valence for Ag0 nanoparticles using XPS—characterization of nanoparticles inside poly (3-sulphopropyl methacrylate) brushes
- 2010
-
Ingår i: Surface and Interface Analysis. - : John Wiley & Sons, Ltd. - 0142-2421 .- 1096-9918. ; 42:6-7, s. 855-858
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of silver nanoparticles (10–20 nm) inside poly (3-sulfopropyl methacrylate) brushes was studied by using transmission electron microscopy, UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). Initially, the silver forms Ag clusters that are stabilised by the anionic side groups of the brush. In the presence of a reducing agent, these clusters aggregate into nanoparticles or films. The apparent oxidation state for silver in the different forms was examined using XPS and a chemical state plot. It was seen that the nanoparticles do not display the same chemical shift as the silver film does. The reason for this observation is suggested to be the final and initial state effects. The latter is related to the relatively high amount of under coordinated or charged surface atoms on these particles.
|
|
| 49. |
- Ramstedt, Madeleine, et al.
(författare)
-
Evaluating Efficacy of Antimicrobial and Antifouling Materials for Urinary Tract Medical Devices : Challenges and Recommendations
- 2019
-
Ingår i: Macromolecular Bioscience. - : John Wiley & Sons. - 1616-5187 .- 1616-5195. ; 19:5
-
Forskningsöversikt (refereegranskat)abstract
- In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient‐days. Of these cases, catheter‐associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health‐care costs of £1–2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary‐tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device‐associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.
|
|
| 50. |
|
|
