FIG. 5.

Survival of S. suis in an acidic environment. Wild-type strain 10 (filled symbols) and mutant strain 10ΔarcA (open symbols) were grown to stationary phase and harvested, and equal numbers of bacteria were suspended in 20 mM Na₂HPO₄-1 mM MgCl₂-25 mM l-arginine-HCl at pH 4 (□), pH 5 (▵), pH 6 (○), and pH 7 (▿). Buffer without l-arginine-HCl served as a control (⋄). The bacteria were incubated at 37°C, and after 1, 2, and 4 h, the number of viable organisms was determined by plating on THY agar. Results are presented as percent survival (CFU count at the indicated time point compared to that of the initial inoculum). Results of a representative experiment of three are shown.