FIG. 3.

Loss of acid tolerance of E. coli O157:H7 strain P1432 upon commencement of growth. After a 90-min challenge at pH 3.0, cells were removed from a mid-exponential-phase culture (A), a mid-exponential-phase culture adapted at pH 5.0 for 1 h (B), or a stationary-phase culture (C) and inoculated in to fresh TPB (pH 7.0). The inoculum was calculated to give approximately 10⁴ viable cells per ml. Samples were taken at various time intervals thereafter, and both acid tolerance (expressed as percent of survival after 90 min at pH 3.0) and growth (expressed as CFU per milliliter) were determined. The error bars represent the standard deviations from the means (n = 3).