FIG 3.

Acid stress response of S. mutans wild-type strain UA159 and Trk mutants. Acid tolerance assays were conducted with unadapted (white bars) and adapted (black bars) cultures incubated for 1 h (A) or 2 h (B) at a killing pH of 3.5. For pH adaptation, cells were preexposed to TYE medium plus 0.5% glucose that was adjusted to pH 5.5. After exposure to the killing pH, cells were plated, and acid tolerance was expressed as percent survivors relative to the total number of CFU present at time zero, just prior to exposure at pH 3.5. #, P < 0.01, and *, P < 0.001, compared to unadapted cultures of the same strain. Values are means and standard errors (SE) from experiments repeated three times, and statistical comparison was performed using a one-way ANOVA.