Figure 3.

Acid-tolerance assays. For acid tolerance, Streptococcus mutans strains were grown either in brain–heart infusion (BHI) broth until mid-exponential phase (OD₆₀₀ ≅ 0.45) or in biofilm medium with glucose (18 mM) plus sucrose (2 mM) (BMGS) on glass slides for 3 days. Brief sonication was used to disperse biofilms. All cultures were washed once with 0.1 M glycine buffer, pH 7.0, and then subjected to acid killing at pH 2.8 for 45 min. The surviving cells were plated on BHI agar plates in triplicate, and expressed as survival rate over time. Data presented here are representatives of more than three independent experiments. Solid symbols represent planktonic cultures and open symbols represent biofilms (BF).