Extensive studies have been conducted on stress adaptation in E. coli O157: H7. However, it is difficult to compare results between laboratories due to strain-to-strain variation in acid tol- erance and variations in the assay conditions used between lab oratories (that is, minimal vs. complex medium, log ary phase cells, different adaptive. and challenge pH conditions etc.) (Cutter and Siragusa 1994; Miller and Kaspar 1994). The complexity of various EHEC responses to different stresses has re- sulted in variation in the techniques and the terminology used to describe these phenomena in food studies. For effective control of resistant pathogens in foods, genetics and physiology of resistant pathogens and mechanisms of survival and resistance develop- ment in stressful environment are necessary. There is a need to in- vestigate potential strain variations in stress resistance,.in relation to the sources, routes of food contamination, and the sensitivity of the at-risk population (Takumi and others 2000). In addition, mechanisms of extracellular sensing and intracellular changes in gene expression of food-borne pathogens in stressful environments need to be investigated (Rowbury 1997; Lazim and Rowbury 2000; Storz and Hengge-Aronis 2000; Rowbury 2001).