70 kDa Salivary Protein Facilitates Streptococcus mutans-Streptococcus gordonii Antagonistic Relationship

Objectives: Previous studies have suggested that Streptococcus mutans and Streptococcus gordonii show an antagonistic relationship in the oral ecosystem. Our main interest was to find a human-derived biomaterial in a form of salivary protein that facilitates this relationship as S. mutans plays a pivotal role in dental caries pathogenesis. The aims of this study were to find salivary proteins that specifically bind to S. mutans and determine their potency in enhancing S. gordonii biofilm growth.
Methods: Five mL of unstimulated saliva samples were collected from 3 healthy volunteers in the same period. The binding affinity of the salivary proteins to S. mutans ATCC^® 25175 was facilitated using a binding buffer (10mM NaHCO₃^-, 5mM KH₂PO₄, 17mM KCl, 0.3mM CaCl₂) and the specific protein were eluted by urea elution buffer (2M urea, 500mM NaCl, 50mM KHPO₄). Target protein profile was visualized on SDS-PAGE agar and its ability to facilitate S. gordonii ATCC^® 10558 biofilm growth was carried out on 96-well microtiter plates followed by incubation at 37°C for 24h. Crystal violet staining was used to measure S. gordonii biofilm growth. The obtained data were analyzed using Pearson correlation test.
Results: A 70 kDa salivary protein showed a binding specificity to S. mutans whole cell and was defined as S. mutans-binding salivary protein (SMBSP). All concentrations of SMBSP (1, 10, 100 µg/mL) showed a similar trend in their potency to act as a pellicle to enhance S. gordonii biofilm growth.
Conclusions: The 70 kDa salivary protein that showed a binding specificity to S. mutans has the potency to facilitate S. gordonii biofilm growth in vitro. This result suggested that 70 kDa salivary protein can be used as a biomaterial to facilitate S. mutans-S. gordonii antagonistic relationship, yet additional studies are required to determine its potency in vivo.