Fig. 2.

Acid killing assay of non-adapted (a) and adapted (b) cells. Strep. mutans UA159 (⧫), TW14D (•), TW14DC (○), TW251 (▴), TW251C (▵) and TW314 (▪) were grown in BHI until mid-exponential phase (OD~0.3). Bacterial cells were then harvested by centrifugation and washed once in 0.1 M glycine buffer, pH 7.0. Acid killing was performed by incubating the cells in 0.1 M glycine buffer, pH 2.8, for 30, 45 and 60 min. For adapted conditions, bacterial cells were incubated in BHI adjusted to pH 5.0 for 1 h prior to the killing assay. The surviving cells were plated in triplicate on BHI agar. Data presented here are the average of three independent experiments; significant difference is indicated by *, P<0.001, and #, P<0.01, compared with the wild-type under similar conditions.