Many Escherichia coli (E. coli) bacteria exist in the environment and in the human gut. Most E. coli bacteria are harmless or cause mild cramping and diarrhea in infected people. However, some strains of E.coli bacteria can release toxin. These are referred to as shigatoxin-producing E. coli (also referred to as enterohemorrhagic E. coli [EHEC] and verotoxigenic E. coli [VTEC]). E. coli O157:H7 is the most well-known of the toxin-producing E. coli. These toxin-producing E. coli can cause more severe diarrhea, bloody diarrhea, serious complications and death.