Figure 4. Acid killing assay of S. mutans wt and gtfBC strains pre-grown the presence or absence of sucrose.

Cells of S. mutans wild-type [WT] and gtfBC-deficient strain [gtfBC] were pre-grown in the buffered minimal medium (pH 7.5) supplemented with glucose or sucrose (20 mM). The cultures were then rapidly acidified to pH 2.8 using glycine solution, and incubated for 0, 0.5 h and 1 h, respectively. The survivors were recovered by plating on TH agar. Survival rate was calculated as the CFU mL⁻¹ at a given time divided by the CFU mL⁻¹ at time zero. Values marked with an asterisk are statistically significantly different between groups (P < 0.05, ANOVA comparison for all pairs using Tukey-Kramer HSD).