Hemolytic uremic syndrome is caused by -a) EIECb) Shigella c) Salmonellad) Cholerae) Klebsiella

**Core Concept**
Hemolytic uremic syndrome (HUS) is a clinical entity characterized by the triad of microangiopathic hemolytic anemia, acute kidney injury, and thrombocytopenia. It is often caused by a bacterial infection that leads to the production of shiga toxins, which damage the endothelial cells and trigger the coagulation cascade.

**Why the Correct Answer is Right**
Shiga toxins produced by certain bacterial strains, such as Shigella dysenteriae type 1, bind to the globotriaosylceramide receptors on the surface of endothelial cells and cause cell death. This leads to the release of von Willebrand factor and other pro-coagulant substances, which in turn cause microvascular thrombosis and subsequent organ dysfunction. The correct answer, Shigella, is a well-documented cause of HUS, particularly in children.

**Why Each Wrong Option is Incorrect**
**Option A:** EIEC (Enteroinvasive Escherichia coli) causes a different type of diarrhea, characterized by invasive bacteria that cause damage to the intestinal epithelium, but it is not typically associated with HUS.
**Option C:** Salmonella species can cause enteric fever and gastrointestinal infections, but they are not commonly linked to HUS.
**Option D:** Cholera is caused by Vibrio cholerae and is characterized by a secretory diarrhea, not HUS.
**Option E:** Klebsiella species can cause urinary tract infections and pneumonia, but they are not typically associated with HUS.

**Clinical Pearl / High-Yield Fact**
Shiga toxin-producing E. coli (STEC), also known as enterohemorrhagic E. coli (EHEC), is a leading cause of HUS in developed countries, particularly in children. The classic presentation of HUS includes a prodromal phase of diarrhea, followed by the development of microangiopathic hemolytic anemia, acute kidney injury, and thrombocytopenia.

**Correct Answer:** B. Shigella