| 1. |
- Andersson, Christin, et al.
(författare)
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Identifying patients at high and low risk of cognitive decline using Rey Auditory Verbal Learning Test among middle-aged memory clinic outpatients
- 2006
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Ingår i: Dementia and Geriatric Cognitive Disorders. - : S. Karger AG. - 1420-8008 .- 1421-9824. ; 21:4, s. 251-259
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To investigate whether application of cutoff levels in an episodic memory test (Rey Auditory Verbal Learning Test, RAVLT) is a useful method for identifying patients at high and low risk of cognitive decline and subsequent dementia. METHODS: 224 patients with memory complaints (mean age = 60.7 years, mean MMSE = 28.2) followed-up at a memory clinic over approximately 3 years were assigned retrospectively to one of three memory groups from their baseline results in RAVLT [severe (SIM), moderate (MIM) or no impairment (NIM)]. These groups were investigated regarding cognitive decline. RESULTS: Patients assigned to SIM showed significant cognitive decline and progressed to dementia at a high rate, while a normal performance in RAVLT at baseline (NIM) predicted normal cognition after 3 years. Patients with MIM constituted a heterogeneous group; some patients deteriorated cognitively, while the majority remained stable or improved. CONCLUSIONS: The application of cutoff levels in RAVLT at baseline showed that patients with severely impaired RAVLT performance were at a high risk of cognitive decline and progression to dementia, while patients with normal RAVLT results did not show cognitive decline during 3 years. Furthermore, the initial degree of memory impairment was decisive in the cognitive prognosis 3 years later.
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| 2. |
- Andersson, Magnus, et al.
(författare)
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A sticky chain model of the elongation and unfolding of escherichia coli P pili under stress
- 2006
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 90:5, s. 1521-1534
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Tidskriftsartikel (refereegranskat)abstract
- A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke’s law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding: elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-versus-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined.
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| 3. |
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| 4. |
- Andersson, Magnus, et al.
(författare)
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Dynamic Force Spectroscopy of E. coli P Pili
- 2006
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 91:7, s. 2717-2725
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Tidskriftsartikel (refereegranskat)abstract
- Surface organelles (so-called pili) expressed on the bacterial membrane mediate the adhesion of Escherichia coli causing urinary tract infection. These pili possess some extraordinary elongation properties that are assumed to allow a close bacterium-to-host contact even in the presence of shear forces caused by urine flow. The elongation properties of P pili have therefore been assessed for low elongation speeds (steady-state conditions). This work reports on the behavior of P pili probed by dynamic force spectroscopy. A kinetic model for the unfolding of a helixlike chain structure is derived and verified. It is shown that the unfolding of the quaternary structure of the PapA rod takes place at a constant force that is almost independent of elongation speed for slow elongations (up to ~0.4 μm/s), whereas it shows a dynamic response with a logarithmic dependence for fast elongations. The results provide information about the energy landscape and reaction rates. The bond length and thermal bond opening and closure rates for the layer-to-layer bond have been assessed to ~0.76 nm, ~0.8 Hz, and ~8 GHz, respectively. The results also support a previously constructed sticky-chain model for elongation of the PapA rod that until now had been experimentally verified only under steady-state conditions.
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| 5. |
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| 6. |
- Andersson, Magnus, et al.
(författare)
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Force measuring optical tweezers system for long time measurements of P pili stability
- 2006
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Ingår i: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV. - : SPIE. - 081946130X - 9780819461308 ; , s. 608810-
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Konferensbidrag (refereegranskat)abstract
- A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.
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