The Effect of Nicotine on Streptococcus mutans Anaerobic Growth

Objectives: The relationship between dental caries and Streptococcus mutans is well known. We have earlier demonstrated that nicotine stimulates S. mutans growth and biofilm formation.  S. mutans is a facultative anaerobe and can grow on occlusal surfaces (aerobically) and subgingivally (anaerobically) contributing to root caries.  All previous studies on S. mutans in relation to nicotine were done aerobically. It is the aim of this study to assess the behavioral difference of S. mutans UA159 in an anaerobic environment at different nicotine concentrations.

Methods: The behavioral aspects that were assessed included sucrose-induced biofilm formation, saliva-induced biofilm formation, metabolic activity, growth kinetics and growth kinetics with H₂O₂ (0.5 and 16.3 mM). The nicotine concentrations investigated in this study ranged between 0.00-32.00 mg/ml.

Results: It was found that biofilm formation in sucrose or saliva medium was significantly better (p<0.05) anaerobically (highest at 8 and 2 mg/ml, respectively) while the presence of oxygen enhanced the metabolic activity of UA159 in a nicotine-dependent concentration manner up to 16 mg/ml. Growth kinetics indicated slower growth of S. mutans aerobically with a maximum absorbance at 0.25 mg/ml of nicotine concentration. With 0.5 mM H₂O₂ the maximum absorbance was noticed in the total absence of nicotine, but no growth was noticed at 16.3 mM.

Conclusions: The absence of oxygen leads the S. mutans to behave differently with some enhanced abilities (biofilm) and some others suppressed (metabolic activity) at different concentrations of nicotine. This suggests that the different microaerophilic environments that S. mutans may grow in will stimulate various effects on the biofilm and growth characteristics of the bacterium.