The influence of ionic strength on the adhesive bond stiffness of oral streptococci possessing different surface appendages as probed using AFM and QCM-D

Adam L. J. Olsson; Narasimhan Arun; Johannes S. Kanger; Henk J. Busscher; Ivan E. Ivanov; Terri A. Camesano; Yun Chen; Diethelm Johannsmann; Henny C. van der Mei; Prashant K. Sharma

doi:10.1039/C2SM26025E

The influence of ionic strength on the adhesive bond stiffness of oral streptococci possessing different surface appendages as probed using AFM and QCM-D

Adam L. J. Olsson,^a Narasimhan Arun,^b Johannes S. Kanger,^b Henk J. Busscher,^a Ivan E. Ivanov,^c Terri A. Camesano,^c Yun Chen,^a Diethelm Johannsmann,^d Henny C. van der Mei^a and Prashant K. Sharma*^a

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* Corresponding authors

^a Department of Biomedical Engineering (FB40), W.J. Kolff Institute, University Medical Center Groningen and University of Groningen, P.O. Box 196, 9700 AD Groningen, The Netherlands
E-mail: p.k.sharma@umcg.nl
Fax: +31-50-363-3159
Tel: +31-50-3633140

^b Nanobiophysics, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, PO Box 217, Enschede, The Netherlands

^c Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA

^d Institute of Physical Chemistry, Clausthal University of Technology, D-38678 Clausthal-Zellerfeld, Germany

Abstract

Bacterial adhesion to surfaces poses threats to human-health, not always associated with adhering organisms, but often with their detachment causing contamination elsewhere. Bacterial adhesion mechanisms may not be valid for their detachment, known to proceed according to a visco-elastic mechanism. Here we aimed to investigate influences of ionic strength on the adhesive bond stiffness of two spherically shaped Streptococcus salivarius strains with different lengths of fibrillar surface appendages. The response of a Quartz-Crystal-Microbalance-with-Dissipation (QCM-D) upon streptococcal adhesion and changes in the ionic strength of the surrounding fluid indicated that the bond stiffness of S. salivarius HB7, possessing a dense layer of 91 nm long fibrils, was unaffected by ionic strength. Atomic-force-microscopic (AFM) imaging in PeakForce-QNM mode showed a small decrease in bond stiffness from 1200 to 880 kPa upon decreasing ionic strength from 57 to 5.7 mM, while Total-Internal-Reflection-Microscopy suggested a complete collapse of fibrils. S. salivarius HBV51, possessing a less dense layer of shorter (63 nm) fibrils, demonstrated a strong decrease in bond stiffness both from QCM-D and AFM upon decreasing the ionic strength, and a partial collapse of fibrils. Probably, the more hydrophobic and less negatively charged long fibrils on S. salivarius HB7 collapse side-on to the cell surface, while the more hydrophilic and negatively charged fibrils of S. salivarius HBV51 remain partially stretched. In summary, we demonstrate how a combination of different methods can yield a description of the structural changes occurring in the interfacial region between adhering, fibrillated streptococci and a substratum surface upon changing the ionic strength.

Soft Matter

The influence of ionic strength on the adhesive bond stiffness of oral streptococci possessing different surface appendages as probed using AFM and QCM-D

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The influence of ionic strength on the adhesive bond stiffness of oral streptococci possessing different surface appendages as probed using AFM and QCM-D

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