Fig. 2.

Acid killing assay of non-adapted (a) and adapted (b) Strep. mutans strains. (a) Strep. mutans wild-type, UA159 (▪), BrpB-deficient mutant, JB409 (○), BrpB-complemented strain, JB409C (•), BrpB- and BrpA-deficient double mutant, JB819 (Δ), and BrpB- and BrpA-complemented strain, JB819C (▴), were grown in BHI until mid-exponential phase (OD₆₀₀ 0.3). Bacterial cells were then harvested by centrifugation and washed twice in 0.1 M glycine, pH 7.0. Acid killing was performed by incubating the bacterial cells in 0.1 M glycine buffer, pH 2.8, for periods of 15, 30 and 45 min. Data presented here are representative of three independent experiments; significant difference is indicated by *, P<0.001, and #, P<0.01, as compared to the wild-type under similar conditions. (b) For adaptive conditions, bacterial cells were incubated in BHI, pH 5.0, for 1 h prior to acid killing. Other details are the same as for (a).