Background: The use of electronic cigarettes (ECIG) has become very common. Consequently, critical analysis of the biological effects of ECIG aerosol deserves attention. Flavorless ECIG aerosol is known to comprise fewer harmful constituents than cigarette smoke. Therefore, we hypothesize that aerosol has less immediate effect on the viability of oral commensal streptococci than smoke. Methods: Survival and growth of four strains of commensal streptococci were measured after exposure to flavorless ECIG aerosol ± nicotine and smoke. Peristaltic pumps were used to transport aerosol or smoke into chambers containing recently seeded colony-forming units (CFUs) of the oral commensal streptococci on agar plates. Bacterial survival and growth, based on colony counts and sizes, were determined 24 h post-exposure. Additionally, aerosol or smoke were delivered into chambers containing pre-adhered streptococci to plastic coverslips and biofilm formation was determined 24 h post-exposure via scanning electron microscopy. Results: The results suggest that flavorless aerosol ± nicotine has a modest effect on bacterial growth both as colonies on agar and as biofilms. In contrast, smoke dramatically decreased bacterial survival and growth in all parameters measured. Conclusion: Unlike cigarette smoke, flavorless ECIG aerosol has only a small effect on the survival and growth of oral commensal streptococci.

The use of electronic cigarettes (ECIG) has become very common. Consequently, critical analysis of the biological effects of ECIG aerosol deserves attention. Since the mouth is the first anatomical cavity exposed to aerosol, the oral bacteria within are also exposed. We hypothesize that while cigarette smoke has a detrimental effect on the survival and growth of oral commensal streptococci, flavorless ECIG aerosol does not. Survival and growth of several strains of commensal streptococci were measured after exposure to flavorless ECIG aerosol ± nicotine and smoke. Peristaltic pumps were used to transport flavorless aerosol ± nicotine or cigarette smoke into chambers containing recently seeded colony forming units of four strains of oral commensal streptococci on agar plates. Bacterial survival and growth, based on colony counts and sizes, were determined 24 hours post-exposure. Lastly, aerosol or smoke were delivered into chambers containing the four strains of streptococci pre-adhered to plastic coverslips. Bacterial survival and growth, as indicated by biofilm formation, were determined 24 hours post-exposure via scanning electron microscopy. The results suggest that flavorless aerosol ± nicotine has a modest effect on bacterial growth both as colonies on agar and as biofilms. In contrast, smoke dramatically decrease bacterial survival and growth in all parameters measured. Therefore, unlike cigarette smoke, flavorless ECIG aerosol has only a small effect on the survival and growth of oral commensal streptococci.