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Wiklund, Krister
Publications (10 of 18) Show all publications
Hanqing, Z., Wiklund, K. & Andersson, M. (2016). A fast and robust circle detection method using isosceles triangles sampling. Pattern Recognition, 54, 218-228.
Open this publication in new window or tab >>A fast and robust circle detection method using isosceles triangles sampling
2016 (English)In: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 54, 218-228 p.Article in journal (Refereed) Published
Abstract [en]

Circle detection using randomized sampling has been developed in recent years to reduce computational intensity. However, randomized sampling is sensitive to noise that can lead to reduced accuracy and false-positive candidates. To improve on the robustness of randomized circle detection under noisy conditions this paper presents a new methodology for circle detection based upon randomized isosceles triangles sampling. It is shown that the geometrical property of isosceles triangles provides a robust criterion to find relevant edge pixels which, in turn, offers an efficient means to estimate the centers and radii of circles. For best efficiency, the estimated results given by the sampling from individual connected components of the edge map were analyzed using a simple clustering approach. To further improve on the accuracy we applied a two-step refinement process using chords and linear error compensation with gradient information of the edge pixels. Extensive experiments using both synthetic and real images have been performed. The results are compared to leading state-of-the-art algorithms and it is shown that the proposed methodology has a number of advantages: it is efficient in finding circles with a low number of iterations, it has high rejection rate of false-positive circle candidates, and it has high robustness against noise. All this makes it adaptive and useful in many vision applications.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Circle detection, Randomized algorithm, Sampling strategy, Isosceles triangles
National Category
Computer Vision and Robotics (Autonomous Systems)
Research subject
Computerized Image Analysis
Identifiers
urn:nbn:se:umu:diva-112312 (URN)10.1016/j.patcog.2015.12.004 (DOI)000372380700017 ()
Funder
Swedish Research Council, 2013-5379
Available from: 2015-12-05 Created: 2015-12-05 Last updated: 2018-01-10Bibliographically approved
Zakrisson, J., Singh, B., Svenmarker, P., Wiklund, K., Zhang, H., Hakobyan, S., . . . Andersson, M. (2016). Detecting Bacterial Surface Organelles on Single Cells using Optical Tweezers. Langmuir, 32(18), 4521-4529.
Open this publication in new window or tab >>Detecting Bacterial Surface Organelles on Single Cells using Optical Tweezers
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2016 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 18, 4521-4529 p.Article in journal (Refereed) Published
Abstract [en]

Bacterial cells display a diverse array of surface organelles that are important for a range of processes such as: intercellular communication, motility and adhesion leading to biofilm formation, infections and bacterial spread. More specifically, attachment to host cells by Gram-negative bacteria are mediated by adhesion pili, which are nm wide and µm long fibrous organelles. Since these pili are significantly thinner than the wavelength of visible light, they cannot be detected using standard light microscopy techniques. At present, there is no fast and simple method available to investigate if a single cell expresses pili while keeping the cell alive for further studies. In this study, we present a method to determine the presence of pili on a single bacterium. The protocol involves imaging the bacterium to measure its size, followed by predicting the fluid drag based on its size using an analytical model, and thereafter oscillating the sample while a single bacterium is trapped by an optical tweezer to measure its effective fluid drag. Comparison between the predicted and the measured fluid drag thereby indicate the presence of pili. Herein, we verify the method using polymer coated silica microspheres and Escherichia coli bacteria expressing adhesion pili. Our protocol, can in real time and within seconds assist single cell studies by distinguishing between piliated and non-piliated bacteria.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Physical Chemistry Materials Engineering
Identifiers
urn:nbn:se:umu:diva-119441 (URN)10.1021/acs.langmuir.5b03845 (DOI)000375809100015 ()27088225 (PubMedID)
Funder
Swedish Research Council, 2013-5379
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2017-11-30Bibliographically approved
Zakrisson, J., Wiklund, K., Servin, M., Axner, O., Lacoursiere, C. & Andersson, M. (2015). Rigid multibody simulation of a helix-like structure: the dynamics of bacterial adhesion pili. European Biophysics Journal, 44(5), 291-300.
Open this publication in new window or tab >>Rigid multibody simulation of a helix-like structure: the dynamics of bacterial adhesion pili
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2015 (English)In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 44, no 5, 291-300 p.Article in journal (Refereed) Published
Abstract [en]

We present a coarse-grained rigid multibody model of a subunit assembled helix-like polymer, e.g., adhesion pili expressed by bacteria, that is capable of describing the polymer's force-extension response. With building blocks representing individual subunits, the model appropriately describes the complex behavior of pili expressed by the gram-negative uropathogenic Escherichia coli bacteria under the action of an external force. Numerical simulations show that the dynamics of the model, which include the effects of both unwinding and rewinding, are in good quantitative agreement with the characteristic force-extension response as observed experimentally for type 1 and P pili. By tuning the model, it is also possible to reproduce the force-extension response in the presence of anti-shaft antibodies, which dramatically changes the mechanical properties. Thus, the model and results in this work give enhanced understanding of how a pilus unwinds under the action of external forces and provide a new perspective of the complex bacterial adhesion processes.

Keyword
Fimbriae, Escherichia coli, Optical tweezers, Simulations, Force spectroscopy
National Category
Biophysics
Identifiers
urn:nbn:se:umu:diva-106000 (URN)10.1007/s00249-015-1021-1 (DOI)000356143100002 ()25851543 (PubMedID)
Available from: 2015-07-07 Created: 2015-07-03 Last updated: 2017-12-04Bibliographically approved
Mortezaei, N., Singh, B., Bullitt, E., Zakrisson, J., Epler, C., Wiklund, K. & Andersson, M. (2015). Structural and biophysical comparison of UPEC and ETEC adhesion fimbriae. Paper presented at 59th Annual Meeting of the Biophysical-Society, Baltimore, February 7-11, 2015. Biophysical Journal, 108(2, suppl 1), 527A-527A.
Open this publication in new window or tab >>Structural and biophysical comparison of UPEC and ETEC adhesion fimbriae
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2015 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 108, no 2, suppl 1, 527A-527A p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

Adhesion fimbriae (pili) of uropathogenic and enterotoxigenic Escherichia coli (UPEC and ETEC, respectively) facilitate adherence of the bacteria to target cells. Fimbriae are absolutely necessary for colonization and biofilm formation in the initiation of disease. The types of fimbriae expressed on the bacterial surface vary with the preferred environmental niche of the bacterial strain. For example, UPEC that express P-pili are most frequently associated pyelonephritis, an infection in the upper urinary tract, whereas bacteria that express type 1 fimbriae commonly cause cystitis through infection of the lower urinary tract. In contrast, ETEC expressing CFA/I and CS2 pili are associated with diarrheal diseases, initiating disease in the small intestines.

Although expressed in different enviroments, these fimbriae share basic structural and biomechanical features. Structurally, they are all long (1-4 μm), thin (7-8 nm diameter) helix-like filaments that extend from the bacterial surface. Biomechanically, they share the ability to be extended into a thinner filament (2-3 nm diameter) by unwinding of the helical filament under a constant force. However, the force required to unwind is specific to each fimbrial type. In addition, the dependence of the force required to unwind a fimbria on the velocity of this unwinding, (that is, the kinetics of unwinding), is also type-specific and highly variable. These biomechanical parameters are dissimilar for UPEC and ETEC expressed fimbriae, separating them into two distinct groups. Using force spectroscopy data, helical reconstructions from electron microscopy data, and computational simulations, we show in this work how these pronounced biomechanical differences may be beneficial for bacterial survival in a given environment.

Place, publisher, year, edition, pages
Cell Press, 2015
National Category
Biophysics
Identifiers
urn:nbn:se:umu:diva-100804 (URN)10.1016/j.bpj.2014.11.2890 (DOI)000362849600276 ()
Conference
59th Annual Meeting of the Biophysical-Society, Baltimore, February 7-11, 2015
Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2017-12-04Bibliographically approved
Zakrisson, J., Wiklund, K., Axner, O. & Andersson, M. (2015). Tethered cells in fluid flows: beyond the Stokes’ drag force approach. Physical Biology, 12, Article ID 056006.
Open this publication in new window or tab >>Tethered cells in fluid flows: beyond the Stokes’ drag force approach
2015 (English)In: Physical Biology, ISSN 1478-3967, E-ISSN 1478-3975, Vol. 12, 056006Article in journal (Refereed) Published
Abstract [en]

Simulations of tethered cells in viscous sub-layers are frequently performed using the Stokes' drag force, but without taking into account contributions from surface corrections, lift forces, buoyancy, the Basset force, the cells' finite inertia, or added mass. In this work, we investigate to what extent such contributions, under a variety of hydrodynamic conditions, influence the force at the anchor point of a tethered cell and the survival probability of a bacterium that is attached to a host by either a slip or a catch bond via a tether with a few different biomechanical properties. We show that a consequence of not including some of these contributions is that the force to which a bond is exposed can be significantly underestimated; in general by similar to 32-46%, where the influence of the surface corrections dominate ( the parallel and normal correction coefficients contribute similar to 5-8 or similar to 23-26%, respectively). The Basset force is a major contributor, up to 20%, for larger cells and shear rates. The lift force and inertia contribute when cells with radii >3 mu m have shear rates>2000 s(-1). Buoyancy contributes significantly for cells with radii > 3 mu m for shear rates<10 s(-1). Since the lifetime of a bond depends strongly on the force, both the level of approximation and the biomechanical model of the tether significantly affect the survival probability of tethered bacteria. For a cell attached by a FimH-mannose bond and an extendable tether with a shear rate of 3000 s(-1), neglecting the surface correction coefficients or the Basset force can imply that the survival probability is overestimated by more than an order of magnitude. This work thus shows that in order to quantitatively assess bacterial attachment forces and survival probabilities, both the fluid forces and the tether properties need to be modeled accurately.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-106875 (URN)10.1088/1478-3975/12/5/056006 (DOI)000362005900010 ()26331992 (PubMedID)
Funder
Swedish Research Council, 2013-5379Swedish Research Council, 621-2008-3280
Available from: 2015-08-11 Created: 2015-08-11 Last updated: 2017-12-04Bibliographically approved
Wiklund, K. & Andersson, M. (2013). Arrangement and method for performing movement analysis. PRV 1250416-3.
Open this publication in new window or tab >>Arrangement and method for performing movement analysis
2013 (English)Patent (Other (popular science, discussion, etc.))
National Category
Software Engineering
Identifiers
urn:nbn:se:umu:diva-80241 (URN)
Patent
PRV 1250416-3 (2013-12-27)
Note

Svensk titel: Arrangemang och metod för att utföra rörelseanalys

Ansök­nings­nummer: SE 1250416-3

Publicer­ings­nummer: SE 536490

Publicerad som: SE536490 C2, SE1250416 A1

Available from: 2013-09-12 Created: 2013-09-12 Last updated: 2018-01-11Bibliographically approved
Zakrisson, J., Wiklund, K., Axner, O. & Andersson, M. (2013). The shaft of the type 1 fimbriae regulates an externalforce to match the FimH catch bond. Biophysical Journal, 104(10), 2137-2148.
Open this publication in new window or tab >>The shaft of the type 1 fimbriae regulates an externalforce to match the FimH catch bond
2013 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 10, 2137-2148 p.Article in journal (Refereed) Published
Abstract [en]

Type 1 fimbriae mediate adhesion of uropathogenic Escherichia coli to host cells. It has been hypothesized that due to their ability to uncoil under exposure to force, fimbriae can reduce fluid shear stress on the adhesin-receptor interaction by which the bacterium adheres to the surface. In this work, we develop a model that describes how the force on the adhesin-receptor interaction of a type 1 fimbria varies as a bacterium is affected by a time-dependent fluid flow mimicking in vivo conditions. The model combines in vivo hydrodynamic conditions with previously assessed biomechanical properties of the fimbriae. Numerical methods are used to solve for the motion and adhesion force under the presence of time-dependent fluid profiles. It is found that a bacterium tethered with a type 1 pilus will experience significantly reduced shear stress for moderate to high flow velocities and that the maximum stress the adhesin will experience is limited to ∼120 pN, which is sufficient to activate the conformational change of the FimH adhesin into its stronger state but also lower than the force required for breaking it under rapid loading. Our model thus supports the assumption that the type 1 fimbria shaft and the FimH adhesin-receptor interaction are optimized to each other, and that they give piliated bacteria significant advantages in rapidly changing fluidic environments.

Keyword
type 1, E coli, pili, optical tweezers, FimH
National Category
Biophysics Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-64463 (URN)10.1016/j.bpj.2013.03.059 (DOI)000319318400008 ()23708354 (PubMedID)
Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2017-12-06Bibliographically approved
Zakrisson, J., Wiklund, K., Axner, O. & Andersson, M. (2012). Helix-like bio-polymers can act as effective dampers for bacteria in flows. European Biophysics Journal, 41(6), 551-560.
Open this publication in new window or tab >>Helix-like bio-polymers can act as effective dampers for bacteria in flows
2012 (English)In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 41, no 6, 551-560 p.Article in journal (Refereed) Published
Abstract [en]

Biopolymers are vital structures for many liv- ing organisms; for a variety of bacteria, adhesion polymers play a crucial role for the initiation of colonization. Some bacteria express, on their surface, attachment organelles (pili) that comprise subunits formed into stiff helix-like structures that possess unique biomechanical properties. These helix-like structures possess a high degree of flexi- bility that gives the biopolymers a unique extendibility. This has been considered beneficial for piliated bacteria adhering to host surfaces in the presence of a fluid flow. We show in this work that helix-like pili have the ability to act as efficient dampers of force that can, for a limited time, lower the load on the force-mediating adhesin-receptor bond on the tip of an individual pilus. The model presented is applied to bacteria adhering with a single pilus of either of the two most common types expressed by uropathogenic Escherichia coli, P or type 1 pili, subjected to realistic flows. The results indicate that for moderate flows (~25 mm/s) the force experienced by the adhesin-receptor interaction at the tip of the pilus can be reduced by a factor of ~6 and ~4, respectively. The uncoiling ability pro- vides a bacterium with a ‘‘go with the flow’’ possibility that acts as a damping. It is surmised that this can be an important factor for the initial part of the adhesion process, in particular in turbulent flows, and thereby be of use for bacteria in their striving to survive a natural defense such as fluid rinsing actions.

Place, publisher, year, edition, pages
Springer: , 2012
Keyword
fimbriae, pili, uncoiling, damping, bacterial adhesion
National Category
Other Physics Topics Biophysics
Research subject
Physics; biology
Identifiers
urn:nbn:se:umu:diva-54018 (URN)10.1007/s00249-012-0814-8 (DOI)
Available from: 2012-04-11 Created: 2012-04-11 Last updated: 2017-12-07Bibliographically approved
Minnhagen, P., Norqvist, P. & Wiklund, K. (2010). ABC-bok för fysiknyfikna. Umeå: Umeå universitet.
Open this publication in new window or tab >>ABC-bok för fysiknyfikna
2010 (Swedish)Book (Other (popular science, discussion, etc.))
Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2010. 60 p.
Keyword
Fysik, populärvetenskap
National Category
Physical Sciences Didactics
Identifiers
urn:nbn:se:umu:diva-44228 (URN)978-91-7459-081-4 (ISBN)
Note
LäromedelAvailable from: 2011-05-26 Created: 2011-05-26 Last updated: 2011-05-27Bibliographically approved
Castelain, M., Koutris, E., Andersson, M., Wiklund, K., Björnham, O., Schedin, S. & Axner, O. (2009). Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili. ChemPhysChem, 10(9-10), 1533-1540.
Open this publication in new window or tab >>Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili
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2009 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 10, no 9-10, 1533-1540 p.Article in journal (Refereed) Published
Abstract [en]

Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:umu:diva-21489 (URN)10.1002/cphc.200900195 (DOI)000267928100027 ()19565578 (PubMedID)
Available from: 2009-04-14 Created: 2009-04-14 Last updated: 2017-12-13Bibliographically approved
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