Escherichia coli O157 : H7 glutamate- and arginine-dependent acid-resistance systems protect against oxidative stress during extreme acid challenge

Abstract

Micro-organisms may simultaneously encounter multiple stresses in their environment. To investigate the protection that several knownEscherichia coliO157 : H7 acid-resistance systems might provide against both oxidative and acid stress, the addition of diamide, a membrane-permeable thiol-specific oxidizing agent, or hydrogen peroxide were used concurrent with acid challenge at pH 2.5 to determine bacterial survival. The addition of either diamide or hydrogen peroxide decreased bacterial survival in a dose-dependent manner forE. coliO157 : H7 during challenge at pH 2.5 following overnight growth in LB MES pH 5.5 (acid-resistance system 1, AR1). In contrast, the presence of either glutamate or arginine during challenge provided significant protection against diamide- and hydrogen peroxide-induced oxidative stress during pH 2.5 acid challenge. Oxidative stress protection during acid challenge requiredgadCandadiAfor the glutamate- (AR2) and arginine- (AR3) dependent acid-resistance systems, respectively. In addition, maximal protection against oxidative stress in the presence of glutamate required a low external pH (pH 2.5), since pH 5.5 did not protect. This study demonstrates that the glutamate- and arginine-dependent acid-resistance systems ofE. coliO157 : H7 can simultaneously protect against oxidative stress during extreme acid challenge.