Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a food-borne bacterial pathogen that causes various diseases in both humans and animals such as hemorrhagic colitis and hemolytic uremic syndrome. Because cattle are the main reservoir of this microorganism, undercooked meat and meat byproducts contaminated with EHEC O157:H7 are most commonly associated with epidemic disease outbreaks. As an enteric pathogen, EHEC O157:H7 enters the body via a fecal-oral route and must survive passage through the gastric stomach at pH 1.5 to 3.5 to establish an infection within the gastrointestinal tracts. Therefore, the ability to resist such acidic environments is important to the pathogenesis of EHEC O157:H7 during a host infection. In this review, we will discuss on the acid resistance (AR) mechanisms induced by EHEC O157:H7 when E. coli encounters acidic environments.

Abstract
 EHEC O157:H7
 Tolerance of EHEC O157:H7 to diverse environmentalconditions
 Endogenous AR systems in EHEC O157:H7
  Four AR systems
  AFI
 Regulatory network of the AR2 system in EHECO157:H7
  Universal regulators
  EHEC O157:H7 specific regulators
 Concluding remarks
 REFERENCES

• Seon Mi Wi(College of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University)
• Jang Won Yoon(College of Veterinary Medicine and Institute of Veterinary Science, Kangwon National University) Corresponding Author