Nanoscale dynamics of streptococcal adhesion to AGE-modified collagen

The adhesion of initial colonizers such asStreptococcus mutansto collagen is critical for dentinal and root caries progression. One of the most described pathological and aging-associated changes in collagen – including dentinal collagen – is the generation of advanced glycation end-products (AGEs) such as methylglyoxal (MGO)-derived AGEs. Despite previous reports suggesting that AGEs alter bacterial adhesion to collagen, the biophysics driving oral streptococcal attachment to MGO-modified collagen remains largely understudied. Thus, the aim of this work was to unravel the dynamics of the initial adhesion ofS. mutansto type-I collagen in the presence and absence of MGO-derived AGEs, by employing bacterial cell force-spectroscopy with atomic force microscopy (AFM). Type-I collagen gels were treated with 10mM MGO to induce AGE formation, which was characterized with microscopy and ELISA. Subsequently, AFM cantilevers were functionalized with livingS. mutansUA 159 orS. sanguinisSK 36 cells and probed against collagen surfaces to obtain force-curves displaying bacterial attachment in real-time, from which the adhesion force, number of events, Poisson analysis, and contour and rupture lengths for each individual detachment event were computed. Furthermore, in-silico docking studies between the relevantS. mutansUA 159 collagen-binding protein SpaP and collagen were computed, in the presence and absence of MGO. Overall, results showed that MGO modification increased both the number and adhesion force of single-unbinding events betweenS. mutansand collagen, without altering the contour or rupture lengths. Both experimental and in-silico simulations suggest that this effect is due to increased specific and non-specific forces and interactions betweenS. mutansUA 159 and MGO-modified collagen substrates. In summary, these results suggest that collagen alterations due to glycation and AGE formation may play a role in early bacterial adherence to oral tissues, associated with conditions such as aging or chronic hyperglycemia, amongst others.