Effect of Nicotine on Streptococcus mutans Sortase Activity

Objectives:  

Streptococcus mutans is the major etiological agent of human dental caries. Tobacco and/or nicotine has a documented effect on S. mutans growth and colonization and increases expression of antigen I/II, as well as GTF and GbpA. Sortase is used by many bacteria, including S. mutans, to facilitate the insertion of certain cell surface proteins including antigen I/II but not GTF or GbpA, if the protein contains an LPXTGX motif. This study examined the indirect effect of nicotine on S. mutans sortase activity.

Methods:  

Wild-type S. mutans NG8, and sortase-defective and -complemented strains were used in this study. Briefly, the strains were treated with various nicotine concentrations in planktonic growth, biofilm metabolism, and sucrose- and saliva-induced biofilm formation assays using microplate technology.

Results:  

The three bacteria did not exhibit any significant difference in various concentrations of nicotine in the planktonic growth assay. All strains had significantly increased (p < 0.05) metabolic activity as the concentration of nicotine increased. However, the sortase-defective and -complemented strains were more sensitive metabolically to nicotine than wild type NG8. All strains had significantly increased sucrose-induced biofilm formation as a result of increasing concentrations of nicotine. However, the sortase-defective strain was less sensitive to nicotine than the wild type NG8. In addition, the sortase-defective strain forms significantly less saliva-induced biofilm than wild type NG8 in the presence of nicotine.

Conclusions:

These results suggest that lower concentrations of nicotine increased planktonic growth, sucrose-induced biofilm formation, and metabolic activity. Higher nicotine concentrations inhibit growth. The saliva-induced biofilm formation assay demonstrates that sortase is up-regulated with nicotine and no biofilm is able to be formed without functional sortase in the absence of sucrose-mediated pathways.