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Keywords:

  • Acid resistance;
  • rpoS;
  • gadB;
  • gadC;
  • Escherichia coli;
  • Glutamate decarboxylase

Abstract

Strains of Escherichia coli K-12, O157:H7, and Shigella flexneri grown to stationary phase in complex unbuffered media can survive for several hours at pH 2.5. This stationary-phase acid resistance phenotype is dependent upon the alternate sigma factor σs and the supplementation of either glutamate or glutamine in the acidified media used for acid challenge. Acid resistance under these defined conditions can be inhibited by the glutamate analog l-trans-pyrrolidine-2,4-dicarboxylic acid which blocks uptake of glutamate/glutamine by selective inhibition. The gadC gene, encoding an inner membrane antiporter essential for the expression of acid resistance, could not be detected in other family members of the Enterobacteriacae.