Escherichia coli O121' is a serotype of Escherichia coli, a species of bacteria that lives in the lower intestines of mammals.http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5602a2.htm Laboratory-Confirmed Non-O157 Shiga Toxin Producing E. Coli, Centers for Disease Control and Prevention, accessed March 16, 2007 The presence of many serotypes of E. coli in animals is beneficial or does not cause disease. However, E. coli O121 has been recognized as a potential disease causing serotype of bacteria. Unlike H7, another pathogenic serotype of E. coli, little is known about the public health significance of O121.
Escherichia coli O121 is also known as a type of "non-O157 Shiga toxin-producing E. coli" or "non-O157 STEC".