FIG. 2.

Susceptibility to reactive oxygen and nitrogen species. (A and B) Salmonella cultures were grown overnight in LB medium, diluted in saline, and plated (100 μl containing 10⁶ CFU) on M9 minimal plates containing 0.2% glucose. Then 15 μl of 3% hydrogen peroxide (A) or paraquat (1 mM) (B) was spotted onto 6-mm-diameter paper disks, the disks were placed onto the bacterial lawn, and the plates were incubated overnight at 37°C. The zone of inhibition was measured on two axes, averaged, and plotted. (C) Susceptibility to acidified nitrite was determined by adding 20 μl of an overnight culture to 2 ml of acidified LB (pH 5) with or without 20 mM sodium nitrite. Bacteria were incubated at 37°C with aeration for 3 and 6 h, and viable cells were enumerated by plating dilutions onto LB agar.