Effect of Nicotine on Streptococcus mutans Adherence
Authors:John Chan, Melissa Langer, Wei-Jen Lin
Mentor:John Chan, Professor of Biological sciences, California State Polytechnic University Pomona
Nicotine users experience more dental caries which are frequently caused by Streptococcus mutans (SM) when it adheres to the surface. Preliminary data showed that nicotine induces biphasic regulations on SM growth, causing larger aggregates and longer chains, suggesting nicotine may affect adherence. The objective is to investigate the effect of nicotine on SM adherence. To study this objective, variables affecting the adherence of SM were evaluated using a microtiter plate method and the degree of adherence was measured in terms of absorbance. SM (ATCC 25175) sub-cultured in TGY agar was used in this study. The variables examined included: growth media (TGY, BHI, Tryptic Soy and Todd-Hewitt), incubation times (0 to 10 hours), dyes (1% crystal violet and 1% safranin), types of wells (flat-bottom, V-bottom, and U-bottom), and different supplements of sucrose (0.10% to 0.25%) and glucose (0.10% to 1.00%). Overnight SM cultures at absorbance of 0.5 were used in a 96-well microtiter plate. After incubation and exposure to the different variables, the non-adhered SM was washed away and adhered SM cells were stained with dye which was measured by a microtiter plate reader. The magnitude of absorbance reading indicates the degree of adherence. After analysis using Student's t-test, the data shows that maximum adherence was detected with 8 hour incubation time, TGY broth, 1% crystal violet, round-bottom microtiter wells, and 0.20% glucose supplement. Under these optimal adherence conditions, the effects of nicotine (10-10 M to 10-1 M) on adherence were tested. The data shows that nicotine enhances the adherence of SM in a dosage-dependent manner with the greatest amount of adherence detected in nicotine concentrations of 10-7 M to 10-6 M. The current study confirms smoking enhances SM adherence, increasing the chances of dental caries as currently reported in the literature.