FIG. 1.

Mutations in ompR result in defective stationary-phase acid tolerance. (A) Cells were grown in minimal EG medium overnight. Unadapted cells (−) were immediately washed and resuspended in fresh pH 3 EG medium to 2 × 10⁸ CFU/ml. Adapted cells (+) were washed and resuspended in pH 4.4 EG medium for adaptation (2 h), after which the cells were washed and resuspended in pH 3 EG medium for challenge. Viable counts were taken at 2 (t2) and 4 (t4) h after challenge. Cell density at t₀ was approximately 2 × 10⁸ CFU/ml. (B) Cells were grown to log phase (2 × 10⁸ CFU/ml) in pH 7.7 EG medium. Unadapted cell cultures were immediately adjusted to pH 3.1. Adapted cultures were adjusted to pH 4.4 for 60 min and then readjusted to pH 3.1. The data represent the means of triplicate experiments with variations ranging less than 50% of the stated percent survival value. Viable counts were taken at 1 (t1) and 2 (t2) h after challenge.