AntigenI/II and Saliva in Streptococcus mutans and Streptococcus intermedius Biofilms

Dental caries and periodontal disease are caused by oral microorganisms organized in biofilms. Streptococcus mutans and Streptococcus intermedius are commensal organisms found in the human oral cavity. S. mutans is frequently associated with dental caries, whereas S. intermedius is often associated with deep-seated purulent infections. Oral streptococci including S. mutants and S. intermedius express a family of surface proteins termed antigen I/II (Ag I/II), which is important for adhesion. Little is known, however, about the role of Ag I/II in biofilm formation. Objectives: To investigate the role of Ag I/II in biofilm formation in the presence or absence of saliva. Methods: Biofilm formation by S. mutans and S. intermedius wild types and their isogenic Ag I/II defective mutants was compared. The cells were grown in polystyrene microtiter plates with TSB or TSB supplemented with saliva in 5% CO₂ at 37°C. Biofilm formation was assessed after 40 h by measuring the optical density of adherent cells stained with safranin. Scanning electron microscopy was also used to assess and visualize biofilm formation. Results: In presence of saliva, the S. mutans antigen I/II defective mutants formed approximately 65% less biofilm than S. mutans wild type. No difference was seen in biofilm formation between the wild type and the Ag I/II mutant when grown in plain TSB medium. Disruption of Ag I/II in S. intermedius showed no effect on the ability to form biofilms irrespective of presence or absence of saliva. These findings were confirmed by scanning electron microscopy. Conclusions: In the presence of saliva, Ag I/II played a significant role in biofilm formation by S. mutans but not by S. intermedius. In the absence of saliva, Ag/II did not seem to play a significant role in biofilm formation by neither S. mutans nor by S. intermedius.