Escherichia coli (E. coli) bacteria are commonly found in the gut of humans and animals. Most strains of E. coli do not cause harm in the bowels, although they can cause infections if they spread to urine or blood. However, a few strains have acquired characteristics that allow them to attach to cells in the gut, invade the lining of the gut and/or produce toxins that cause damage or secretory malfunctions of gut cells. One such toxin, the "Shiga" toxin is capable of causing diarrhea that may be watery or bloody. Strains that produce Shiga toxin are also called 'STEC' strains. If an STEC strain also has acquired the ability to adhere to cells in the gut, it is referred to as an 'enterohemorrhagic E. coli' or EHEC. The most common EHEC is E. coli 0157:H7, but other variants exist, including the one that is causing the 2011 E. coli outbreak that originated in Germany.