A 4-year-old boy gives the history of bloody diarrhea and now hospitalized for oliguria and hypeension. With which organism is he most likely infected?

The case is descriptive of hemolytic uremic syndrome associated with infection with E. coli O157:H7. This strain of E. coli produces phage-associated Shiga toxins (Stx-1 and/or Stx-2) that are functionally and antigenically similar to that produced by Shigella dysenteriae. None of the other organisms listed are associated with hemolytic uremic syndrome, although some do cause a bloody diarrhea. C. perfringens causes watery diarrhea.