Hemolytic uremic syndrome is most commonly caused by toxins produced by which organism?

• A. Staphylococcus aureus
• B. Shigella dysenteriae
• C. Escherichia coli O157:H7
• D. Vibrio cholerae

Answer: (C)

Hemolytic uremic syndrome arises when Shiga toxin damages the lining of small vessels, especially in the kidneys. The organism most commonly responsible is Shiga toxin–producing Escherichia coli, particularly the O157:H7 serotype. After ingestion, these bacteria release Shiga toxin that injures renal microvasculature, leading to platelet activation and microthrombi formation, which fragments red blood cells and causes hemolysis. This sequence produces the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. While Shigella dysenteriae can also produce Shiga toxin and cause HUS, it is less common. Organisms like Staphylococcus aureus or Vibrio cholerae don’t typically cause HUS via Shiga toxin, so they aren’t usual culprits.