S. Typhimurium tolerance represents a persister state characterized by phenotypic variation.

Bacterial CFU were monitored after multiple rounds of treatment with (A) ampicillin, 100 μg/mL, (B) hydrogen peroxide, 1.25 mM, or (C) pH 3.0. Presence of stress is indicated by filled rectangles and regrowth without stress by open rectangles. Alternatively, (D-F) independent colonies were grown to late log phase (dotted line) and challenged with the corresponding stressors as indicated by the filled rectangles. Mean of > 3 independent experiments are shown; error bars denote SEM.