The effect of nicotine on growth of Streptococcus mutans.

There is little information available concerning the effects of nicotine on oral bacteria; and in particular, Streptococcus mutans, an important microbe in the etiology of dental caries. To test the effects of nicotine, Streptococcus mutans were incubated in either 0 or 10(-1)-10(-7) M concentrations of nicotine and then plated onto mitis-salivarius-bacitracin agar. Colonies were counted and treatment groups compared. Both 10(-1) and 10(-2) M nicotine caused total inhibition of bacterial growth, while 10(-3) and 10(-4) M produced significantly more colonies than control. Also, 10(-6) and 10(-7) M nicotine produced a significant reduction in the mean number of colonies. These results suggest a biphasic, dosage-dependent effect of nicotine on the growth of Streptococcus mutans. Since 10(-3) M nicotine has been reported within the saliva of smokeless tobacco users, use of these products could stimulate growth of Streptococcus mutans and possibly place the user at increased risk for dental caries.