Chemo-mechanical preparation of the root canal leaves behind viable bacteria which can lead to treatment failure. Materials used inside the root canal should possess antimicrobial properties and also ...resist disintegration in the presence of biofilm.
Gutta-percha, three root canal sealers (Pulp Canal Sealer, AH Plus and BioRoot RCS) and materials used to make posts (a metal and a resin) were evaluated. Their antimicrobial activity against Enterococcus faecalis in direct contact was assessed by scanning electron microscopy and live-dead staining using confocal microscopy over a period of eight weeks. The materials’ structural integrity was assessed by scanning electron microscopy.
The antimicrobial activity of the materials varied. The metal alloy posts as well as BioRoot RCS sealer did not allow any biofilm accumulation; but gutta-percha, Pulp Canal Sealer and resin from fibre-reinforced posts encouraged thick biofilm accumulation. Microstructural changes were observed in AH Plus (washout) and BioRoot (crystal deposition) in contact with biofilm. The Pulp Canal and BioRoot RCS sealers exhibited a modified ion leaching pattern in contact with microbially loaded media.
The microbial challenge affected the material microstructure in some of the materials tested and allowed biofilm accumulation. Although clinical success depends on a number of factors, materials that are structurally sound and exhibit antimicrobial properties are preferable for endodontic therapy and tooth restoration involving entry in the root canal.
Giant Piezoelectricity on Si for Hyperactive MEMS Baek, S. H.; Park, J.; Kim, D. M. ...
Science (American Association for the Advancement of Science),
11/2011, Letnik:
334, Številka:
6058
Journal Article
Recenzirano
Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been ...constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(MG 1/3 Nb 2/3 )O₃-PbTiO₃ (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO₃ template layer with superior piezoelectric coefficients (e 31,f = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.
Individual-based modelling of biofilms Kreft, J U; Picioreanu, C; Wimpenny, J W ...
Microbiology (Society for General Microbiology),
11/2001, Letnik:
147, Številka:
Pt 11
Journal Article
Recenzirano
Odprti dostop
Understanding the emergence of the complex organization of biofilms from the interactions of its parts, individual cells and their environment, is the aim of the individual-based modelling (IbM) ...approach. This IbM is version 2 of BacSim, a model of Escherichia coli colony growth, which was developed into a two-dimensional multi-substrate, multi-species model of nitrifying biofilms. It was compared with the established biomass-based model (BbM) of Picioreanu and others. Both models assume that biofilm growth is due to the processes of diffusion, reaction and growth (including biomass growth, division and spreading). In the IbM, each bacterium was a spherical cell in continuous space and had variable growth parameters. Spreading of biomass occurred by shoving of cells to minimize overlap between cells. In the BbM, biomass was distributed in a discrete grid and each species had uniform growth parameters. Spreading of biomass occurred by cellular automata rules. In the IbM, the effect of random variation of growth parameters of individual bacteria was negligible in contrast to the E. coli colony model, because the heterogeneity of substrate concentrations in the biofilm was more important. The growth of a single cell into a clone, and therefore also the growth of the less abundant species, depended on the randomly chosen site of attachment, owing to the heterogeneity of substrate concentrations in the biofilm. The IbM agreed with the BbM regarding the overall growth of the biofilm, due to the same diffusion-reaction processes. However, the biofilm shape was different due to the different biomass spreading mechanisms. The IbM biofilm was more confluent and rounded due to the steady, deterministic and directionally unconstrained spreading of the bacteria. Since the biofilm shape is influenced by the spreading mechanism, it is partially independent of growth, which is driven by diffusion-reaction. Chance in initial attachment events modifies the biofilm shape and the growth of single cells because of the high heterogeneity of substrate concentrations in the biofilm, which again results from the interaction of diffusion-reaction with spreading. This stresses the primary importance of spreading and chance in addition to diffusion-reaction in the emergence of the complexity of the biofilm community.
A computational model explaining formation of mushroom-like biofilm colonies is proposed in this study. The biofilm model combines for the first time cell growth with twitching motility in a ...three-dimensional individual-based approach. Model simulations describe the tendency of motile cells to form flat biofilms spreading out on the substratum, in contrast with the immotile variants that form only round colonies. These computational results are in good qualitative agreement with the experimental data obtained from Pseudomonas aeruginosa biofilms grown in flowcells. Simulations reveal that motile cells can possess a serious ecological advantage by becoming less affected by mass transfer limitations. Twitching motility alone appears to be insufficient to generate mushroom-like biofilm structures with caps on stalks. Rather, a substrate limitation-induced detachment of motile cells followed by reattachment could explain this intriguing effect leading to higher-level biofilm structure.
We have simulated a nitrifying biofilm with one ammonia and one nitrite oxidising species in order to elucidate the effect of various extracellular polymeric substance (EPS) production scenarios on ...biofilm structure and function. The individual-based model (IbM) BacSim simulates diffusion of all substrates on a two-dimensional lattice. Each bacterium is individually simulated as a sphere of given size in a continuous, three-dimensional space. EPS production kinetics was described by a growth rate dependent and an independent term (Leudeking-Piret equation). The structure of the biofilm was dramatically influenced by EPS production or capsule formation. EPS production decreased growth of producers and stimulated growth of non-producers because of the energy cost involved. For the same reason, EPS accumulation can fall as its rate of production increases. The patchiness and roughness of the biofilm decreased and the porosity increased due to EPS production. EPS density was maximal in the middle of the vertical profile. Introduction of binding forces between like cells increased clustering.
Abstract
Background
Post-traumatic stress disorder (PTSD) occurs more commonly in military veterans than the general population. Whilst current therapies are effective, up to half of veterans ...commencing treatment do not complete it. Reconsolidation of Traumatic Memories (RTM) protocol is a novel, easy to train, talking therapy with promising findings. We examine the feasibility of undertaking an efficacy trial of RTM in veterans.
Methods
A parallel group, single-centre randomised controlled feasibility trial with a post-completion qualitative interview study. Sixty military veterans were randomised 2:1 to RTM (
n
= 35) or Trauma Focussed Cognitive Behaviour Therapy (CBT) (
n
= 25). We aimed to determine the rate of recruitment and retention, understand reasons for attrition, determine data quality and size of efficacy signal. We explored veterans’ perceptions of experiences of joining the trial, the research procedures and therapy, and design improvements for future veteran studies. Military veterans with a diagnosis of PTSD or complex PTSD, and clinically significant symptoms, were recruited between January 2020 and June 2021. Primary outcome was feasibility using pre-determined progression criteria alongside PTSD symptoms, with depression, recovery, and rehabilitation as secondary outcomes. Data were collected at baseline, 6, 12, and 20 weeks. Interviews (
n
= 15) were conducted after 20 weeks. Both therapies were delivered by trained charity sector provider therapists.
Results
Participants’ mean age was 53 years, the mean baseline PTSD symptoms score assessed by the Post-traumatic Stress Checklist (PCL-5) was 57 (range 0–80). Fifty had complex PTSD and 39 had experienced ≥ 4 traumas. Data were analysed at 20 weeks for feasibility outcomes (
n
= 60) and mental health outcomes (
n
= 45). Seven of eight progression criteria were met. The RTM group experienced a mean 18-point reduction on the PCL-5. TFCBT group participants experienced a mean reduction of eight points. Forty-eight percent of the RTM group no longer met diagnostic criteria for PTSD compared to 16% in the TFCBT group. All veterans reported largely positive experiences of the therapy and research procedures and ways to improve them.
Conclusion
RTM therapy remains a promising psychological intervention for the treatment of PTSD, including complex PTSD, in military veterans. With specific strengthening, the research protocol is fit for purpose in delivering an efficacy trial.
Trial registration
ISRCTN registration no 10314773 on 01.10.2019.
Full trial protocol: available on request or downloadable at ISRCTN reg. no. 10314773.
The generic, quantitative, spatially explicit, individual-based model BacSim was developed to simulate growth and behaviour of bacteria. The potential of this approach is in relating the properties ...of microscopic entities - cells - to the properties of macroscopic, complex systems such as biofilms. Here, the growth of a single Escherichia coli cell into a colony was studied. The object-oriented program BacSim is an extension of Gecko, an ecosystem dynamics model which uses the Swarm toolkit for multi-agent simulations. The model describes bacterial properties including substrate uptake, metabolism, maintenance, cell division and death at the individual cell level. With the aim of making the model easily applicable to various bacteria under different conditions, the model uses as few as eight readily obtainable parameters which can be randomly varied. For substrate diffusion, a two-dimensional diffusion lattice is used. For growth-rate-dependent cell size variation, a conceptual model of cell division proposed by Donachie was examined. A mechanistic version of the Donachie model led to unbalanced growth at higher growth rates, whereas including a minimum period between subsequent replication initiations ensured balanced growth only if this period was unphysiologically long. Only a descriptive version of the Donachie model predicted cell sizes correctly. For maintenance, the Herbert model (constant specific rate of biomass consumption) and for substrate uptake, the Michaelis-Menten or the Best equations were implemented. The simulator output faithfully reproduced all input parameters. Growth characteristics when maintenance and uptake rates were proportional to either cell mass or surface area are compared. The authors propose a new generic measure of growth synchrony to quantify the loss of synchrony due to random variation of cell parameters or spatial heterogeneity. Variation of the maximal uptake rate completely desynchronizes the simulated culture but variation of the volume-at-division does not. A new measure for spatial heterogeneity is introduced: the standard deviation of substrate concentrations as experienced by the cells. Spatial heterogeneity desynchronizes population growth by subdividing the population into parts synchronously growing at different rates. At a high enough spatial heterogeneity, the population appears to grow completely asynchronously.
Comparative Genomics of Listeria Species Glaser, P.; Frangeul, L.; Buchrieser, C. ...
Science (American Association for the Advancement of Science),
10/2001, Letnik:
294, Številka:
5543
Journal Article
Recenzirano
Listeria monocytogenes is a food-borne pathogen with a high mortality rate that has also emerged as a paradigm for intracellular parasitism. We present and compare the genome sequences of L. ...monocytogenes (2,944,528 base pairs) and a nonpathogenic species, L. innocua (3,011,209 base pairs). We found a large number of predicted genes encoding surface and secreted proteins, transporters, and transcriptional regulators, consistent with the ability of both species to adapt to diverse environments. The presence of 270 L. monocytogenes and 149 L. innocua strain-specific genes (clustered in 100 and 63 islets, respectively) suggests that virulence in Listeria results from multiple gene acquisition and deletion events.
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