FIG. 2.

Log reduction of L. monocytogenes and L. innocua parent and ΔsigB strains for log-phase cells (A) and stationary-phase cells (B) after exposure to acid stress. Strains with higher log reduction showed greater sensitivity to acid stress (e.g., L. monocytogenes ΔsigB showed a 5.5-log reduction while L. monocytogenes parent strain 10403S showed a 2-log reduction; the ΔsigB strain is thus more sensitive to acid stress). Experiments were performed in three independent trials, and data shown represent the averages of these trials; error bars show the standard deviations. Bacterial numbers after acid stress were analyzed using the general linear model with Tukey's multiple-comparisons procedure; bars labeled with different letters indicate bacterial numbers that differed significantly (P < 0.05), while bars labeled with identical letters indicate bacterial numbers that did not differ significantly.