Survival after a stress of one hour at pH 2.3.

Values in the table are percentage survival ± standard deviation, which results from three independent experiments. Viability was assessed by CFU count on LB plates. The percentage survival represents the ratio between the CFU counted after and before stress. NT means not tested. Bacteria grown overnight in LBG pH 5 were diluted 1/1000 in M9 acidified to pH 2.3 and challenged for one hour. Cultures and stresses were done in anoxic conditions. When indicated 20 mM L-Arg, L-Lys, L-Orn or L-Gln were added to the medium during the challenge.