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Streptococcus milleri” group (SMG) are human commensals often associated with purulent infections including dental abscesses. Many bacteria, through their adhesins, have learned to exploit host extracellular matrix (ECM) components, including proteoglycans, as receptor molecules for cell attachment to facilitate tissue colonization and invasion processes.
Objectives: To investigate the interactions of SMG with small leucine-rich repeat proteoglycans (SLRPs) using real-time biospecific analysis, via a BIAcore® 3000 system.
Methods: Direct assays were employed involving binding of whole bacteria cells with either purified ovine gingival SLRPs (containing decorin and biglycan with and without dermatan sulphate glycosaminoglycan chains), alveolar bone SLRPs (decorin and biglycan with and without chondroitin sulphate chains) and recombinant decorin or biglycan (with and without chondroitin sulphate chains). SLRPs were immobilised to a sensor chip and disease or commensal isolates injected over the surface. Binding was measured as a change in surface plasmon resonance.
Results: SMG demonstrated considerably more binding to intact SLRPs compared to core protein. Of the species examined,
S. intermedius in particular demonstrated high levels of binding, for example, 30C and 84C, achieving 1532.2 RU and 1133.7 RU, respectively. Several
S. anginosus isolates, showed relatively low or no binding to intact SLRPs. For the SLRP core proteins,
S. anginosus and
S. constellatus isolates showed no binding with only
S intermedius isolates (30C, 84C and 127/95) displaying a small amount of binding.
Conclusions: Differential binding characteristics were exhibited both within and between SMG species for glycosylated and non-glycosylated forms of SLRPs, although commensal strains demonstrated more consistent binding. There was greater binding to intact SLRPs, suggesting adhesion may be mediated through the sulphated glycosaminoglycan chains. Binding was greater for gingival SLRPs carrying dermatan sulphate chains. These findings may provide useful information regarding the mechanism of SMG pathogenesis within the ECM.
Funded by Wales Office for Research and Development