Intermolecular Forces and Enthalpies in the Adhesion of Streptococcus Mutans and Antigen I/II Deficient Mutant to Laminin Films

Department of Biomedical Engineering, University Medical Center Groningen, and University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.; Laboratory of Physical Chemistry and Colloid Science, Wageningen University, P.O. Box 8038, 6700 EK Wageningen, The Netherlands; Department of Oral Biology, Faculty of Dentistry, University of Oslo, N0316 Oslo, Norway

^* To whom correspondence should be addressed. Email: h.c.van.der.mei{at}med.umcg.nl.

	Abstract

The antigen I/II family of surface proteins is expressed by most oral streptococci, including Streptococcus mutans and mediates specific adhesion to, amongst others, salivary films and extracellular matrix proteins. In this study we showed that an antigen I/II deficient S. mutans isogenic mutant IB03987 was nearly unable to adhere to laminin films under flow due to lack of specific interactions (0.8 and 1.1 x 10⁶ cm^-2 for pH 5.8 and 6.8, respectively), as compared with the parent strain LT11 (21.8 and 26.1 x 10⁶ cm^-2). Adhesion of both the parent and mutant strain was slightly higher at pH 6.8 than at pH 5.8. In line, AFM experiments demonstrated that the parent strain experienced less repulsion upon approach of a laminin film than did its mutant. Upon retraction, combined specific and non-specific adhesion forces were stronger for the parent strain (up to -5.0 and -4.9 nN for pH 5.8 and 6.8, respectively) than for the mutant (up to -1.5 and -2.1 nN), which was only able to interact through non-specific interactions. Enthalpy is released upon adsorption of laminin to the surface of the parent strain, but not upon adsorption to IB03987. Comparison of the adhesion forces in AFM with those reported for specific ligand-receptor complexes, yields the conclusion that the number of antigen I/II binding sites for laminin on S. mutans LT11 is in the order of 6 x 10⁴ per organism, probably arranged along exterior surface structures, as visualized here with immuno-electron microscopy.