Which of the following is the most important virulence factor for enteroinvasive E. coli (EIEC) pathogenesis?

Explanation

## Enteroinvasive E. coli (EIEC) Virulence Mechanism **Key Point:** EIEC causes disease through bacterial invasion of the intestinal epithelium and colonic mucosa, not toxin production. The invasion plasmid antigen (Ipa) is essential for this pathogenic mechanism. ### Virulence Factor Profile of EIEC | Virulence Factor | Mechanism | EIEC | ETEC | EAEC | STEC | |---|---|---|---|---|---| | Invasion plasmid (Ipa) | Epithelial invasion | **Yes** | No | No | No | | Heat-labile toxin (LT) | Enterotoxin | No | **Yes** | No | No | | Heat-stable toxin (ST) | Enterotoxin | No | **Yes** | No | No | | Shiga toxin | Cytotoxin | No | No | No | **Yes** | | Adhesins (fimbriae) | Adherence | Yes | Yes | **Yes** | Yes | **High-Yield:** EIEC is the invasive pathotype — it invades and destroys the intestinal mucosa, causing bloody diarrhea and dysentery-like illness. This is fundamentally different from ETEC (toxin-mediated secretory diarrhea) and STEC (Shiga toxin-mediated hemolytic uremic syndrome). **Clinical Pearl:** EIEC diarrhea is typically bloody and accompanied by fever and tenesmus, mimicking *Shigella* dysentery. The invasion plasmid allows the organism to penetrate the epithelium and trigger an inflammatory response. **Mnemonic:** **EIEC = Invasive** (like Shigella); **ETEC = Enterotoxin** (like Vibrio); **STEC = Shiga toxin** (like Shigella dysenteriae).