Shiga toxin-producing E coli (STEC) are named for the cytotoxic toxins they produce. There are at least two antigenic forms of the toxin referred to as Shiga-like toxin 1 and Shiga-like toxin 2. STEC has been associated with, Hemorrhagic colitis Severe diarrhea Hemolytic uremic syndrome resulting acute renal failure Microangiopathic hemolytic anemia Thrombocytopenia Of the E coli serotypes that produce Shiga toxin, O157:H7 is the most common. STEC O157:H7 does not use sorbitol, unlike most other E coli, and is negative (clear colonies) on sorbitol MacConkey agar (sorbitol is used instead of lactose); which serves as an impoant criterion that distinguishes it from other strains of E. coli. O157:H7 strains also are negative on MUG tests. Many of the non-O157 serotypes may be sorbitol positive when grown in culture. Ref: Brooks G.F. (2013). Chapter 15. Enteric Gram-Negative Rods (Enterobacteriaceae). In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.