Effects of Electronic Cigarette Liquid on the Growth, Biofilm Formation, Lactic Acid Production, and Stress Tolerance of Streptococcus mutans

Cigarette smoking is associated with numerous respiratory diseases. To help mitigate the adverse effects of cigarette smoke on human health, different strategies have been introduced, with the most recent strategy being the introduction of electronic cigarettes (e-cigarettes). However, there is a lack of information regarding the effect of e-cigarettes on humans, including its effect on oral health. While some studies have explored the effects of e-cigarettes on the oral cavity, little is known about their effects on the oral microbiota, especially those that cause dental caries. To determine the effects of e-cigarettes on the leading cause of dental caries, we evaluated its effect on the growth, biofilm formation, lactic acid production, induced autolysis, acid stress, and oxidative stress tolerance of Streptococcus mutans, the main causative agent of dental caries. Our results showed a decrease in S. mutans growth with increasing e-liquid concentration. E-liquid concentrations higher than or equal to 10% inhibited S. mutans growth. Furthermore, e-liquid nicotine content had no significant effect on S. mutans growth at sub-inhibitory e-liquid concentrations of 5% (p > 0.05). The results also revealed that S. mutans biofilm formation and lactic acid production did not significantly differ between treatments with and without 5% e-liquid (p > 0.05). Additionally, the rate of autolysis in S. mutans was not significantly affected by exposure to a sub-inhibitory concentration of e-liquid regardless of the nicotine content (p > 0.05). Finally, the acid stress tolerance with or without adaptive response and oxidative stress tolerance by hydrogen peroxide was not significantly different between S. mutans grown with or without the sub-inhibitory concentration of the e-liquid (p > 0.05). These findings suggest that e-cigarettes may not significantly impact the physiology of S. mutans. However, it is important to emphasize that e-cigarettes are not without health risks and that the long-term health effects of e-cigarettes are still under investigation.