FIG. 6.

Acid resistance of exponential-phase E. coli O157 strains at 37°C. Strains C9490 (● and ○) and NCTC 12079 (▴ and ▵) were grown to the stationary phase, diluted in fresh TSB (10⁶ CFU · ml⁻¹), grown to a concentration of 10⁸ CFU · ml⁻¹, and then inoculated (1:10) into TSB acidified to pH 3 with HCl without an additive (solid symbols) or supplemented with 50 mM undissociated acetic acid (open symbols). Each curve shows the average values obtained from at least two independent experiments. The mean standard deviation shown for each curve varied between 0.3 and 0.5.