How does EIEC differ from other diarrheagenic E. coli in terms of pathology and stool?

• A. EIEC invades colonic mucosa producing inflammatory dysentery with blood and pus; stool mimics shigellosis.
• B. EIEC produces Shiga toxin causing HUS.
• C. EIEC causes persistent watery diarrhea via fimbriae.
• D. EIEC is nonpathogenic.

Answer: (A)

Enteroinvasive E. coli causes disease by invading the colonic mucosa, triggering an inflammatory response that resembles Shigella infection. This invasion leads to inflammatory dysentery with fever, abdominal cramps, and stools that contain blood and pus from neutrophils in the lumen. The illness is driven by mucosal invasion rather than toxin production, which is why the stool appears inflammatory rather than purely watery. In contrast, other diarrheagenic E. coli cause disease mainly through toxins or noninvasive mechanisms: Shiga-toxin–producing strains (not EIEC) cause hemorrhagic colitis with potential HUS; enterotoxigenic E. coli cause profuse watery diarrhea via enterotoxins; enteropathogenic E. coli cause persistent watery diarrhea, especially in infants. Therefore, the invasion of the colon with inflammatory dysentery and blood–pus-containing stool best differentiates EIEC from other DEC.