Arginine-dependent acid resistance in Salmonella enterica serovar Typhimurium

Abstract

Salmonella enterica serovar Typhimurium does not survive a pH 2.5 acid challenge under conditions similar to those used for Escherichia coli. Here, we provide evidence that S. enterica serovar Typhimurium can display arginine-dependent acid resistance (AR) provided the cells are grown under anoxic conditions and not under the microaerobic conditions used for assessment of AR in E. coli. The role of the arginine decarboxylase pathway in Salmonella AR was shown by the loss of AR in mutants lacking adiA, which encodes arginine decarboxylase; adiC, which encodes the arginine-agmatine antiporter; or adiY, which encodes an AraC-like regulator. Transcription of adiA and adiC was found to be dependent on AdiY, anaerobiosis, and acidic pH.

FIG. 1.

Arginine-dependent AR of stationary-phase S. enterica serovar Typhimurium cells. Stationary-phase cells grown in LBG at pH 5 were challenged in EG mineral medium, pH 2.5, at an initial concentration of approximately 5 × 10⁵ CFU/ml. Percent survival is depicted as follows: open bars, survival after 1 h without l-arginine; solid bars, survival with l-arginine after 1 h; gray bars, survival with l-arginine after 2 h. All experiments were performed twice in triplicate. The detection limit of the experiment was 5 × 10² CFU/ml.

FIG. 2.

Arginine-dependent AR of stationary-phase S. enterica serovar Typhimurium DT104 strain BAA-188. Stationary-phase cells grown in LBG at pH 5 were challenged in EG mineral medium, pH 2.5, with 20 mM l-arginine at an initial concentration of approximately 5 × 10⁵ CFU/ml. Survival after 1 h (open bars) and 2 h (black bars) is depicted. All experiments were performed twice in triplicate. WT, wild type.