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.
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.
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.
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.
Keywords: Biofilm, Caries, Microbiology and Tobacco
See more of: Cariology Research - Microbiological Studies / Biofilm