Microbial competition in porous environments can select against rapid biofilm growth

Microbes often live in dense communities called biofilms where competition between strains and species is fundamental to both evolution and community function. While biofilms are commonly found in soil-like porous environments, the study of microbial interactions has largely focused on biofilms growing on flat, planar surfaces. Here we use novel microfluidic experiments, mechanistic models, and game theory to study how porous media hydrodynamics can mediate competition between bacterial genotypes. Our experiments reveal a fundamental challenge faced by microbial strains that live in porous environments: cells that rapidly form biofilms tend to block their access to fluid flow and redirect resources to competitors. To understand how these dynamics influence the evolution of bacterial growth rates we couple a model of flow-biofilm interaction with a game theory analysis. This shows that hydrodynamic interactions between competing genotypes give rise to an evolutionarily stable growth rate that stands in stark contrast with that observed in typical laboratory experiments: cells within a biofilm can outcompete other genotypes by growing more slowly. Our work reveals that hydrodynamics can profoundly affect how bacteria compete and evolve in porous environments, the habitat where most bacteria live

To fill or not to fill: a qualitative cross-country study on dentists' decisions in managing non-cavitated proximal caries lesions

BACKGROUND: This study aimed to identify barriers and enablers for dentists managing non-cavitated proximal caries lesions using non- or micro-invasive (NI/MI) approaches rather than invasive and restorative methods in New Zealand, Germany and the USA. METHODS: Semi-structured interviews were conducted, focusing on non-cavitated proximal caries lesions (radiographically confined to enamel or the outer dentine). Twelve dentists from New Zealand, 12 from Germany and 20 from the state of Michigan (USA) were interviewed. Convenience and snowball sampling were used for participant recruitment. A diverse sample of dentists was recruited. Interviews were conducted by telephone, using an interview schedule based on the Theoretical Domains Framework (TDF). RESULTS: The following barriers to managing lesions non- or micro-invasively were identified: patients' lacking adherence to oral hygiene instructions or high-caries risk, financial pressures and a lack of reimbursement for NI/MI, unsupportive colleagues and practice leaders, not undertaking professional development and basing treatment on what had been learned during training, and a sense of anticipated regret (anxiety about not restoring a proximal lesion in its early stages before it progressed). The following enablers were identified: the professional belief that remineralisation can occur in early non-cavitated proximal lesions and that these lesions can be arrested, the understanding that placing restorations weakens the tooth and inflicts a cycle of re-restoration, having up-to-date information and supportive colleagues and work environments, working as part of a team of competent and skilled dental practitioners who perform NI/MI (such as cleaning or scaling), having the necessary resources, undertaking ongoing professional development and continued education, maintaining membership of professional groups and a sense of professional and personal satisfaction from working in the patient's best interest. Financial aspects were more commonly mentioned by the German and American participants, while continuing education was more of a focus for the New Zealand participants. CONCLUSIONS: Decisions on managing non-cavitated proximal lesions were influenced by numerous factors, some of which could be targeted by interventions for implementing evidence-based management strategies in practice

Individual bacterial cells can use spatial sensing of chemical gradients to direct chemotaxis on surfaces

Swimming bacteria navigate chemical gradients using temporal sensing to detect changes in concentration over time. Here we show that surface-attached bacteria use a fundamentally different mode of sensing during chemotaxis. We combined microfluidic experiments, massively parallel cell tracking and fluorescent reporters to study how Pseudomonas aeruginosa senses chemical gradients during pili-based ‘twitching’ chemotaxis on surfaces. Unlike swimming cells, we found that temporal changes in concentration did not induce motility changes in twitching cells. We then quantified the chemotactic behaviour of stationary cells by following changes in the sub-cellular localization of fluorescent proteins as cells are exposed to a gradient that alternates direction. These experiments revealed that P. aeruginosa cells can directly sense differences in concentration across the lengths of their bodies, even in the presence of strong temporal fluctuations. Our work thus overturns the widely held notion that bacterial cells are too small to directly sense chemical gradients in space

Interactive Boundary Element Analysis for Engineering Design

Structural design of mechanical components is an iterative process that involves multiple stress analysis runs; this can be time consuming and expensive. Significant improvements in the eciency of this process can be made by increasing the level of interactivity. One approach is through real-time re-analysis of models with continuously updating geometry. Three primary areas need to be considered to accelerate the re-solution of boundary element problems. These are re-meshing the model, updating the boundary element system of equations and re-solution of the system. Once the initial model has been constructed and solved, the user may apply geometric perturbations to parts of the model. The re-meshing algorithm must accommodate these changes in geometry whilst retaining as much of the existing mesh as possible. This allows the majority of the previous boundary element system of equations to be re-used for the new analysis. For this problem, a GMRES solver has been shown to provide the fastest convergence rate. Further time savings can be made by preconditioning the updated system with the LU decomposition of the original system. Using these techniques, near real-time analysis can be achieved for 3D simulations; for 2D models such real-time performance has already been demonstrated

Bacteria solve the problem of crowding by moving slowly

Bacteria commonly live attached to surfaces in dense collectives containing billions of cells1. While it is known that motility allows these groups to expand en masse into new territory2,3,4,5, how bacteria collectively move across surfaces under such tightly packed conditions remains poorly understood. Here we combine experiments, cell tracking and individual-based modelling to study the pathogen Pseudomonas aeruginosa as it collectively migrates across surfaces using grappling-hook-like pili3,6,7. We show that the fast-moving cells of a hyperpilated mutant are overtaken and outcompeted by the slower-moving wild type at high cell densities. Using theory developed to study liquid crystals8,9,10,11,12,13, we demonstrate that this effect is mediated by the physics of topological defects, points where cells with different orientations meet one another. Our analyses reveal that when defects with topological charge +1/2 collide with one another, the fast-moving mutant cells rotate to point vertically and become trapped. By moving more slowly, wild-type cells avoid this trapping mechanism and generate collective behaviour that results in faster migration. In this way, the physics of liquid crystals explains how slow bacteria can outcompete faster cells in the race for new territory

Fragmentation of High-spin Stretched States in the (p,n) Reaction on 36-Ar and 40-Ca

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Search for a State at E_x = 2.6MeV in 20-Na via the 20-Ne(p,n)20-Na Reaction and Possible Breakout from the Hot CNO Cycle

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

A Comparison of Three Child OHRQoL Measures.

Comparing oral health-related quality of life (OHRQoL) measures can facilitate selecting the most appropriate one for a particular research question/setting. Three child OHRQoL measures Child Perceptions Questionnaire (CPQ11⁻14), the Child Oral Health Impact Profile (COHIP) and the Caries Impacts and Experiences Questionnaire for Children (CARIES-QC) were used with 335 10- to 13-year-old participants in a supervised tooth-brushing programme in New Zealand. The use of global questions enabled their validity to be examined. Assessments were conducted at baseline and after 12 months. All three measures had acceptable internal consistency reliability. There were moderate, positive correlations among their scores, and all showed differences in the impact of dental caries on OHRQoL, with children with the highest caries experience having the highest scale scores. Effect sizes were used to assess meaningful change. The CPQ11⁻14 and the CARIES-QC showed meaningful change. The COHIP-SF score showed no meaningful change. Among children reporting improved OHRQoL, baseline and follow-up scores differed significantly for the CPQ11⁻14 and CARIES-QC measures, although not for the COHIP-SF. The three scales were broadly similar in their conceptual basis, reliability and validity, but responsiveness of the COHIP-SF was questionable, and the need to compute two different scores for the CARIES-QC meant that its administrative burden was considerably greater than for the other two measures. Replication and use of alternative approaches to measuring meaningful change are suggested

Children’s rights in their oral health care: How responsive are oral health professionals to children’s rights

Research on children’s rights in oral health care is lacking, and this study aims to partially fill this gap. In 2015, we conducted research in one region of New Zealand using video methods to explore the rights of 22 children during a specific oral health treatment, the placement of stainless steel crowns. Our findings show that many children did not receive a professional standard of care, there were gaps in the delivery and standard of care, and there were numerous examples of children’s rights’ violations. At the same time, however, some of the children’s dental practitioners’ (CDPs) actions may have been acceptable practice within the profession if children’s rights have not yet fully been embedded into the practice of oral health care workers. We conclude with a discussion of the implications of our findings and suggestions for a more rights based standard of oral health care

High-Spin Stretched States in Nuclei Excited via (p,n) Reactions

This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440