Starvation conferred less acid tolerance to E. coli O157: H7 than did stationary phase (Cheville and others 1996), However, starved or stationary phase cells showed significantly more acid tolerance than acid adapted (growth at pH 5) mid- and late-log. phase cells The rpoS-regulated proteins of E. coli O157: H7 produced in the stationary phase enhanced tolerance to a variety of chemical and physical challenges (Hengge-Aronis 1993a, 1993b; Arnold and Kaspar 1995; Cheville and others 1996). An rpos mutant less heat and salt tolerant than wild-type E. coli O157: H7 and survived poorly in dry, fermented sausage (pH 4.8, oth salt, 1.9% moisture) (Cheville and others 1996). Hall and (1995) noted that many of the pH stress-induced proteins w also induced in S. typhimurium in response to other stresses that low pH caused the cross-induction of heat shock proteir.