Cells swimming in confined environments are attracted by surfaces. We measure the steady-state distribution of smooth-swimming bacteria (Escherichia coli) between two glass plates. In agreement with ...earlier studies, we find a strong increase of the cell concentration at the boundaries. We demonstrate theoretically that hydrodynamic interactions of the swimming cells with solid surfaces lead to their reorientation in the direction parallel to the surfaces, as well as their attraction by the closest wall. A model is derived for the steady-state distribution of swimming cells, which compares favorably with our measurements. We exploit our data to estimate the flagellar propulsive force in swimming E. coli.
Bacterial flagellar filaments grow at their distal ends, from flagellin that travels through a central channel ∼2 nm in diameter. The flagellin is extruded from the cytoplasm by a pump powered by a ...proton motive force (PMF). We measured filament growth in cells near the mid-exponential-phase with flagellin bearing a specific cysteine-for-serine substitution, allowing filaments to be labeled with sulfhydryl-specific fluorescent dyes. We labeled filaments first with a green maleimide dye and then, following an additional period of growth, with a red maleimide dye. The contour lengths of the green and red segments were measured. The average lengths of red segments (∼2.3 μm) were the same regardless of the lengths of the green segments from which they grew (ranging from less than 1 to more than 9 μm in length). Thus, flagellar filaments do not grow at a rate that decreases exponentially with length, as formerly supposed. If flagellar filaments were broken by viscous shear, the broken filaments continued to grow. Identical results were obtained whether flagellin was expressed from fliC on the chromosome under the control of its native promoter or on a plasmid under the control of the arabinose promoter.
Cells of Escherichia coli are able to swim up gradients of chemical attractants by modulating the direction of rotation of their flagellar motors, which spin alternately clockwise (CW) and ...counterclockwise (CCW). Rotation in either direction has been thought to be symmetric and exhibit the same torques and speeds. The relationship between torque and speed is one of the most important measurable characteristics of the motor, used to distinguish specific mechanisms of motor rotation. Previous measurements of the torque–speed relationship have been made with cells lacking the response regulator CheY that spin their motors exclusively CCW. In this case, the torque declines slightly up to an intermediate speed called the "knee speed" after which it falls rapidly to zero. This result is consistent with a "power-stroke" mechanism for torque generation. Here, we measure the torque–speed relationship for cells that express large amounts of CheY and only spin their motors CW. We find that the torque decreases linearly with speed, a result remarkably different from that for CCW rotation. We obtain similar results for wild-type cells by reexamining data collected in previous work. We speculate that CCW rotation might be optimized for runs, with higher speeds increasing the ability of cells to sense spatial gradients, whereas CW rotation might be optimized for tumbles, where the object is to change cell trajectories. But why a linear torque–speed relationship might be optimum for the latter purpose we do not know.
When grown in a rich medium on agar, many bacteria elongate, produce more flagella, and swim in a thin film of fluid over the agar surface in swirling packs. Cells that spread in this way are said to ...swarm. The agar is a solid gel, with pores smaller than the bacteria, so the swarm/agar interface is fixed. Here we show, in experiments with Escherichia coli, that the swarm/air interface also is fixed. We deposited MgO smoke particles on the top surface of an E. coli swarm near its advancing edge, where cells move in a single layer, and then followed the motion of the particles by dark-field microscopy and the motion of the underlying cells by phase-contrast microscopy. Remarkably, the smoke particles remained fixed (diffusing only a few micrometers) while the swarming cells streamed past underneath. The diffusion coefficients of the smoke particles were smaller over the virgin agar ahead of the swarm than over the swarm itself. Changes between these two modes of behavior were evident within 10-20 μm of the swarm edge, indicating an increase in depth of the fluid in advance of the swarm. The only plausible way that the swarm/air interface can be fixed is that it is covered by a surfactant monolayer pinned at its edges. When a swarm is exposed to air, such a monolayer can markedly reduce water loss. When cells invade tissue, the ability to move rapidly between closely opposed fixed surfaces is a useful trait.
Narrative literature is used to teach a variety of social work subjects; however, there are few studies that examine the impact on students. This article describes an assignment requiring the ...selection of a work of fiction or biography by undergraduate social work students enrolled in an interpersonal communication class at an Australian University. Books needed to contain a description of an individual whose life experiences were different from the student's. In an online learning group, students reflected on what they learned from the main character, on something they shared in common and whether they would look forward to serving the person if they met them in their professional social work roles. Themes from their responses are presented in this paper and critical reflections on the assignment are offered. The list of books chosen by the students is also provided.
Abstract
Background
Despite high-quality cardiopulmonary resuscitation (CPR), early defibrillation, and antiarrhythmic medications, some patients remain in refractory ventricular fibrillation (VF) ...during out-of-hospital cardiac arrest. These patients have worse outcomes compared to patients who respond to initial treatment. Double sequential external defibrillation (DSED) and vector change (VC) defibrillation have been proposed as viable options for patients in refractory VF. However, the evidence supporting the use of novel defibrillation strategies is inconclusive. The objective of this study is to compare two novel therapeutic defibrillation strategies (DSED and VC) against standard defibrillation for patients with treatment refractory VF or pulseless ventricular tachycardia (pVT) during out-of-hospital cardiac arrest.
Research question
Among adult (≥ 18 years) patients presenting in refractory VF or pulseless ventricular tachycardia (pVT) during out-of-hospital cardiac arrest, does DSED or VC defibrillation result in greater rates of survival to hospital discharge compared to standard defibrillation?
Methods
This will be a three-arm, cluster randomized trial with repeated crossover conducted in six regions of Ontario, Canada (Peel, Halton, Toronto, Simcoe, London, and Ottawa), over 3 years. All adult (≥ 18 years) patients presenting in refractory VF (defined as patients presenting in VF/pVT and remaining in VF/pVT after three consecutive standard defibrillation attempts during out-of-hospital cardiac arrest of presumed cardiac etiology will be treated by one of three strategies: (1) continued resuscitation using standard defibrillation, (2) resuscitation involving DSED, or (3) resuscitation involving VC (change of defibrillation pads from anterior-lateral to anterior-posterior pad position) defibrillation. The primary outcome will be survival to hospital discharge. Secondary outcomes will include return of spontaneous circulation (ROSC), VF termination after the first interventional shock, VF termination inclusive of all interventional shocks, and number of defibrillation attempts to obtain ROSC. We will also perform an a priori subgroup analysis comparing rates of survival for those who receive “early DSED,” or first DSED shock is shock 4–6, to those who receive “late DSED,” or first DSED shock is shock 7 or later.
Discussion
A well-designed randomized controlled trial employing a standardized approach to alternative defibrillation strategies early in the treatment of refractory VF is urgently required to determine if the treatments of DSED or VC defibrillation impact clinical outcomes.
Trial registration
ClinicalTrials.gov
NCT04080986
. Registered on 6 September 2019.
Little is known about the health service utilization of women sexually assaulted by their intimate partners, as compared with those sexually assaulted by other perpetrators. To address this gap, we ...describe the use of acute care services post-victimization, as well as a broad range of survivor and assault characteristics, across women assaulted by current or former intimate partners, other known assailants, and strangers.
Information was gathered from individuals presenting to 30 hospital-based sexual assault and domestic violence treatment centres using a standardized data collection form. We examined the data from 619 women 16 years of age or older who were sexually assaulted by one assailant.
Women sexually assaulted by a current or former intimate partner were less likely than those assaulted by another known assailant or a stranger to have been administered emergency contraception (p < 0.001) or prophylaxis for sexually transmitted infections (p < 0.001), and counselled for potential use of HIV post-exposure prophylaxis (p < 0.001). However, these women were more likely than those in the other two groups to have had their injuries documented with photographs (p < 0.001), have undergone a risk assessment (p = 0.008), and/or have engaged in safety planning (p < 0.001).
Women sexually assaulted by current or former intimate partners utilized services offered by sexual assault and domestic violence treatment centres differently than those assaulted by other known assailants and strangers. This may reflect their different health, forensic, and social needs, as well as the importance of offering care tailored to their particular circumstances.
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