## E. coli O157:H7 and STEC Management **Key Point:** Antibiotic therapy in STEC is controversial and may worsen outcomes by increasing toxin release. Supportive care is the standard approach. ### Characteristics of STEC O157:H7 | Feature | Detail | | --- | --- | | Toxin | Shiga toxin (Stx1 and/or Stx2) — inactivates 60S ribosome | | Motility | Non-motile (lacks H antigen; O157:H7 notation) | | Clinical presentation | Hemorrhagic colitis, watery → bloody diarrhea | | Complication | HUS (microangiopathic hemolytic anemia + thrombocytopenia + AKI) | | Antibiotic use | **CONTRAINDICATED** — increases toxin release and HUS risk | **High-Yield:** STEC O157:H7 is **non-motile** (no H antigen) and produces **Shiga toxin** that causes **HUS**. ### Why Antibiotics Are Avoided 1. Cell lysis releases more Shiga toxin into bloodstream 2. Increased toxin absorption → systemic toxemia 3. Higher risk of HUS and mortality 4. **Standard of care:** Fluid resuscitation, electrolyte correction, supportive care **Clinical Pearl:** Antimotility agents (loperamide) are also contraindicated — they increase intestinal transit time and toxin absorption. **Warning:** A common exam trap is listing fluoroquinolones or aminoglycosides as first-line for STEC. They are NOT recommended and may cause harm.
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