Effects of pyridoxal (PL) on growth (A) and biofilm formation (B). For growth effects, Streptococcus mutans was grown in brain heart infusion broth with different concentrations (mM) of PL, and the culture optical density was continuously monitored using Bioscreen C. For biofilm formation, S. mutans was grown in biofilm medium with glucose and sucrose (BMGS) with different concentrations of PL (mM) using 96-well plates. After 24 h, biofilms were stained with 0.1% crystal violet and then measured by spectrophotometry. Symbols **, * and # indicate differences in growth rate (A) or biofilms (B) at P < 0.001, P < 0.01 and P < 0.05, respectively, when compared with controls that received no PL.