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Journal of Bacteriology, September 1999, p. 5210-5218, Vol. 181, No. 17
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Effect of Ionic Strength on Initial Interactions of Escherichia coli with Surfaces, Studied On-Line by a Novel Quartz Crystal Microbalance Technique

Karen Otto,1 Hans Elwing,2 and Malte Hermansson1,*

Department of Cell and Molecular Biology, Microbiology,1 and Department of Cell and Molecular Biology, Interface Biophysics,2 Göteborg University, Göteborg, Sweden

Received 7 April 1999/Accepted 30 June 1999

A novel quartz crystal microbalance (QCM) technique was used to study the adhesion of nonfimbriated and fimbriated Escherichia coli mutant strains to hydrophilic and hydrophobic surfaces at different ionic strengths. This technique enabled us to measure both frequency shifts (Delta f), i.e., the increase in mass on the surface, and dissipation shifts (Delta D), i.e., the viscoelastic energy losses on the surface. Changes in the parameters measured by the extended QCM technique reflect the dynamic character of the adhesion process. We were able to show clear differences in the viscoelastic behavior of fimbriated and nonfimbriated cells attached to surfaces. The interactions between bacterial cells and quartz crystal surfaces at various ionic strengths followed different trends, depending on the cell surface structures in direct contact with the surface. While Delta f and Delta D per attached cell increased for nonfimbriated cells with increasing ionic strengths (particularly on hydrophobic surfaces), the adhesion of the fimbriated strain caused only low-level frequency and dissipation shifts on both kinds of surfaces at all ionic strengths tested. We propose that nonfimbriated cells may get better contact with increasing ionic strengths due to an increased area of contact between the cell and the surface, whereas fimbriated cells seem to have a flexible contact with the surface at all ionic strengths tested. The area of contact between fimbriated cells and the surface does not increase with increasing ionic strengths, but on hydrophobic surfaces each contact point seems to contribute relatively more to the total energy loss. Independent of ionic strength, attached cells undergo time-dependent interactions with the surface leading to increased contact area and viscoelastic losses per cell, which may be due to the establishment of a more intimate contact between the cell and the surface. Hence, the extended QCM technique provides new qualitative information about the direct contact of bacterial cells to surfaces and the adhesion mechanisms involved.

* Corresponding author. Mailing address: Department of Cell and Molecular Biology, Microbiology, Box 462, Göteborg University, 405 30 Göteborg, Sweden. Phone: (46)-31-7732574. Fax: (46)-31-7732599. E-mail: Malte.Hermansson{at}gmm.gu.se.

Journal of Bacteriology, September 1999, p. 5210-5218, Vol. 181, No. 17
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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