I. Introduction
Contamination of vegetables with E.coli O157 may occur at different stage from cultivation to transportation[7]. Vegetables grown in soil fertilized by animal manure have a great chance to be contaminated with E.coli O157[11]. E.coli O157:H7 can enter the lettuce tissue when lettuce seeds are grown in manure fertilized soil[12]. Some vegetables like spinach may be contaminated by manure fertilized soil, or by irrigation with water mixed with sewage or by contaminated surface water irrigation [13]. Vegetables used for preparing salads may be the possible routes of transmission if they had been grown in soil fertilized by human wastes or animal manure. Vegetables grown in soil fertilized by human waste carry different kinds of microorganisms[14]. E. coli O157 can be also transmitted from vegetables used for salads by hands