| 1. |
- Andersson, Magnus, et al.
(författare)
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A structural basis for sustained bacterial adhesion : Biomechanical properties of CFA/I Pili
- 2012
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Ingår i: Journal of Molecular Biology. - : Elsevier. - 0022-2836 .- 1089-8638. ; 415:5, s. 918-928
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Tidskriftsartikel (refereegranskat)abstract
- Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease worldwide. Adhesion pili (or fimbriae), such as the CFA/I (colonization factor antigen I) organelles that enable ETEC to attach efficiently to the host intestinal tract epithelium, are critical virulence factors for initiation of infection. We characterized at single organelle level the intrinsic biomechanical properties and kinetics of individual CFA/I pili, demonstrating that weak external forces (7.5 pN) are sufficient to unwind the intact helical filament of this prototypical ETEC pilus and that it quickly regains its original structure when the force is removed. While the general relationship between exertion of force and an increase in the filament length for CFA/I pili associated with diarrheal disease is analogous to that of P-pili and type 1 pili, associated with urinary tract and other infections, the biomechanical properties of these different pili differ in key quantitative details. Unique features of CFA/I pili, including the significantly lower force required for unwinding, the higher extension speed at which the pili enter a dynamic range of unwinding, and the appearance of sudden force drops during unwinding can be attributed to morphological features of CFA/I pili including weak layer-to-layer interactions between subunits on adjacent turns of the helix, and the approximately horizontal orientation of pilin subunits with respect to the filament axis. Our results indicate that ETEC CFA/I pili are flexible organelles optimized to withstand harsh motion without breaking, resulting in continued attachment to the intestinal epithelium by the pathogenic bacteria that express these pili.
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| 2. |
- Andersson, Magnus, et al.
(författare)
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Differentiating pili expressed by enterotoxigenic and uropathogenic escherichia coli with optical tweezers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Enterotoxigenic Escherichia coli (ETEC) attach to the host epithelium in the intestinal tract via specific adhesion organelles expressed on the cell membrane. We investigate, by force measuring optical tweezers, the intrinsic biomechanical properties and kinetics of the colonization factor I (CFA/I) at a single pilus level. The measurements indicate that CFA/I pili are helix-like structures that can both be unraveled to a linearized polymer by applying a small external force, 7.5 ± 1.5 pN but also regain its helix-like structure when the applied force is reduced. The data confirm that layer-to-layer interactions, that stabilize the helix-like structure, are much weaker than the interactions found in pili expressed by Uropathogenic Escherichia coli (UPEC). It is also found, contrary to previous results assessed from UPEC pili, that the CFA/I undergo in some cases a sudden structural change, a force drop of ~2 pN, when unraveled from the helix-like configuration to an open helical linearized fiber. These data suggest a rotation of the filament about its helical axis, followed by a region in which the force required to extend the pili further increases rapidly. During this final elongation to a super-extended fiber, CFA/I pili do not show any structural transition as seen for UPEC pili. In addition, the CFA/I pili show faster kinetics than UPEC pili that allows for a larger dynamic regime of in vivo shear forces. The unfolding and refolding possibility points toward an organelle that has evolved to allow for dynamic damping of external forces and handling of harsh motion without breaking.
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| 3. |
- Axner, Ove, 1957-, et al.
(författare)
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Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers
- 2011
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Ingår i: Bacterial adhesion. - Berlin : Springer Berlin/Heidelberg. ; , s. 301-313
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Bokkapitel (refereegranskat)abstract
- Optical tweezers (OT) are a technique that, by focused laser light, can both manipulate micrometer sized objects and measure minute forces (in the pN range) in biological systems. The technique is therefore suitable for assessment of bacterial adhesion on an individual adhesin-receptor and single attachment organelle (pili) level. This chapter summarizes the use of OT for assessment of adhesion mechanisms of both non-piliated and piliated bacteria. The latter include the important helix-like pili expressed by uropathogenic Escherichia coli (UPEC), which have shown to have unique and intricate biomechanical properties. It is conjectured that the large flexibility of this type of pili allows for a redistribution of an external shear force among several pili, thereby extending the adhesion lifetime of bacteria. Systems with helix-like adhesion organelles may therefore act as dynamic biomechanical machineries, enhancing the ability of bacteria to withstand high shear forces originating from rinsing flows such as in the urinary tract. This implies that pili constitute an important virulence factor and a possible target for future anti-microbial drugs.
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| 4. |
- Axner, Ove, et al.
(författare)
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Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy
- 2010
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Ingår i: Single molecule spectroscopy in chemistry, physics and biology. - Berlin, Heidelberg : Springer. - 9783642025969 ; , s. 337-362
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Konferensbidrag (refereegranskat)abstract
- Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
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| 5. |
- Axner, Ove, et al.
(författare)
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Unraveling the secrets of bacterial adhesion organelles using single molecule force spectroscopy
- 2010. - 96
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Ingår i: Springer series in chemical physics. - : Springer Verlag. - 9783642025969 ; , s. 337-362
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Many types of bacterium express micrometer-long attachment organelles (so called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Forcemeasuring ptical tweezers (FMOT) have since then been used to unravel the iomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated and the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g. urine flow. It has been found that anytypes of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
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| 6. |
- Björnham, Oscar, 1976-
(författare)
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A study of bacterial adhesion on a single-cell level by means of force measuring optical tweezers and simulations
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The intriguing world of microbiology is nowadays accessible for detailed exploration at a single–molecular level. Optical tweezers are a novel instrument that allows for non–invasive manipulation of single cells by the sole use of laser light and operates on the nano– and micrometer scale which corresponds to the same length scale as living cells. Moreover, forces within the field of microbiology are typically in the picoNewton range which is in accordance with the capability of force measuring optical tweezers systems. Both these conformabilities imply that force measuring optical tweezers is suitable for studies of single living cells. This thesis focuses on the mechanisms of bacterial attachments to host cells which constitute the first step in bacterial infection processes. Bacteria bind specifically to host receptors by means of adhesins that are expressed either directly on the bacterial membrane or on micrometer–long adhesion organelles that are called pili. The properties of single adhesin–receptor bonds that mediate adherence of the bacterium Helicobacter pylori are first examined at various acidities. Further on, biomechanical properties of P pili expressed by Escherichia coli are presented to which computer simulations, that capture the complex kinetics of the pili structure and precisely replicate measured data, are applied. Simulations are found to be a powerful tool for investigations of adhesive attributes of binding systems and are utilized in the analyses of the specific binding properties of P pili on a single–pilus level. However, bacterial binding systems generally involve a multitude of adhesin–receptor bonds. To explore bacterial attachments, the knowledge from single–pilus studies is brought into a full multipili attachment scenario which is analyzed by means of theoretical treatments and simulations. The results are remarkable in several aspects. Not only is it found that the intrinsic properties of P pili are composed in an optimal combination to promote strong multipili bindings. The properties of the pili structure itself are also found to be optimized with respect to its in vivo environment. Indeed, the true meaning of the attributes derived at a single–pilus level cannot be unraveled until a multipili–binding system is considered. Whereas detailed studies are presented for the helix–like P pili expressed by Gram–negative Escherichia coli, conceptual studies are presented for the open coil–like T4 pili expressed by Gram–positive Streptococcus pneumoniae. The structural and adhesive properties of these two types of pili differ considerably. These dissimilarities have far–reaching consequences on the adhesion possibilities at both single–pilus and multipili levels which are discussed qualitatively. Moreover, error analyses of conventional data processing methods in dynamic force spectroscopy as well as development of novel analysis methods are presented. These findings provide better understanding of how to perform refined force measurements on single adhesion organelles as well as how to improve the analyses of measurement data to obtain accurate parameter values of biomechanical entities. In conclusion, this thesis comprises a study of bacterial adhesion organelles and the way they cooperate to establish efficient attachment systems that can successfully withstand strong external forces that acts upon bacteria. Such systems can resist, for instance, rinsing effects and thereby allow bacteria to colonize their host. By understanding the complexity, and thereby possible weaknesses, of bacterial attachments, new targets for combating bacterial infections can be identified.
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| 7. |
- Björnham, Oscar, et al.
(författare)
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Absolutely continuous copulas with prescribed support constructed by differential equations, with an application in toxicology
- 2022
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Ingår i: Communications in Statistics - Theory and Methods. - : Taylor & Francis. - 0361-0926 .- 1532-415X. ; 51:19, s. 6601-6625
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Tidskriftsartikel (refereegranskat)abstract
- A new method for constructing absolutely continuous two-dimensional copulas by differential equations is presented. The copulas are symmetric with respect to reflection in the opposite diagonal. The support of the copula density may be prescribed to arbitrary opposite symmetric hypographs of invertible functions, containing the diagonal. The method is applied to toxicological probit modeling, where new compatibility conditions for the probit parameters are derived.
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| 8. |
- Björnham, Oscar, et al.
(författare)
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BioCon - A model for pathogens and biofilm in drinking water distribution systems
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- En modell för biologisk kontamination av dricksvattensystem är utvecklad som ett komplement till kommersiella mjukvaror. Modellen benämns Biofilm contamination model (BioCon), vilken utgörs av delmodeller för transport och biofilmer. De dominerande processerna beskrivs genom ett system av partiella differentialekvationer. BioCon inkluderar även en numerisk lösare för de biofysikaliska modellerna och visualisering av den tidsupplösta kontaminationen i systemet. BioCon är utformad för att kunna hantera många olika biologiska agens och miljöparametrar genom parametrisering av de styrande ekvationerna. De två patogenerna Escherichia coli och Cryptosporidium spp. utgör pilotagens i denna rapport och relevanta egenskaper hos dem diskuteras. Förslag på parametrisering ges för E. coli baserad främst på publicerad litteratur men också till del från preliminär data från laboratorieexperiment genomförda under detta projekt. Modellstrukturen av de viktigaste komponenterna såsom transport, inbindning/dissociation, utveckling av biofilm, och påverkan av temperatur, desinfektionsmedel och näringsämnen, är utformade för att ge upphov till beteenden som överensstämmer med rapporterade experimentell data och teoretiska modeller. Huvuddragen i BioCon har på detta sätt blivit verifierade med avseende på nuvarande kunskapsläge, vilket presenteras i denna rapport. Däremot har en omfattande och kvantitativ validering av BioCon, genom jämförelse med experimentell data för samma system av agens, miljöfaktorer och flöden, ej kunnat genomföras inom ramen för detta projekt. Detta rekommenderas som en framtida studie.
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| 9. |
- Björnham, Oscar, 1976-, et al.
(författare)
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Catch-Bond behavior of bacteria binding by slip bonds
- 2010
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 99:5, s. 1331-1341
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that multipili-adhering bacteria expressing helix-like pili binding by slip bonds can show catch-bond behavior. When exposed to an external force, such bacteria can mediate adhesion to their hosts by either of two limiting means: sequential or simultaneous pili force exposure (referring to when the pili mediate force in a sequential or simultaneous manner, respectively). As the force is increased, the pili can transition from sequential to simultaneous pili force exposure. Since the latter mode of adhesion gives rise to a significantly longer bacterial adhesion lifetime than the former, this results in a prolongation of the lifetime, which shows up as a catch-bond behavior. The properties and conditions of this effect were theoretically investigated and assessed in some detail for dual-pili-adhering bacteria, by both analytical means and simulations. The results indicate that the adhesion lifetime of such bacteria can be prolonged by more than an order of magnitude. This implies that the adhesion properties of multibinding systems cannot be directly conveyed to the individual adhesion-receptor bonds.
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| 10. |
- Björnham, Oscar, 1976-, et al.
(författare)
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Dynamic force spectroscopy of the Helicobacter pylori BabA-Lewis b binding
- 2009
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Ingår i: Biophysical Chemistry. - Amsterdam : Elsevier. - 0301-4622 .- 1873-4200. ; 143:1-2, s. 102-105
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Tidskriftsartikel (refereegranskat)abstract
- The binding strength of the Helicobacter pylori adhesin–receptor complex BabA-ABO/Lewis b has been analyzed by means of dynamic force pectroscopy. High-resolution measurements of rupture forces were performed in situ on single bacterial cells, expressing the high-affinity binding BabA adhesin, by the use of force measuring optical tweezers. The resulting force spectra revealed the mechanical properties of a single BabA–Leb bond. It was found that the bond is dominated by one single energy barrier and that it is a slipbond. The bond length and thermal off-rate were assessed to be 0.86±0.07 nm and 0.015±0.006 s−1, respectively.
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