Pathogenic and nonpathogenic E. coli cells in the stationary phase were substantially more acid tolerant than cells in the log phase (Buchanan and The acid tolerance of 0157: H7 induced by the stationary phase or starvation was not dependent upon adaptation (Miller and Kaspar 1994; Arnold and Kaspar 1995). Three acid resistance (AR) systems have been iden- tified in the stationary phase of all E. coli (Lin and others 1995, 1996, Bearson and others 1997; Audia and others 2001). The sys- tem. induced depended on the type of medium and the growth conditions (Audia and others 2001). The three complex medium dependent acid resistance systems included an oxidative system (AR1) and two fermentative acid resistance systems involving a glutamate decarboxylase (AR2) and an arginine d. (AR3) (Lin and others 1995, 1996).