What characterizes enteroaggregative E. coli (EAEC) and what is its typical clinical pattern?

• A. Attaching and effacing lesions via a type III secretion system.
• B. Invasion of mucosa with abdominal pus.
• C. Stacked-brick adherence pattern via aggregative adherence fimbriae; causes persistent watery diarrhea.
• D. Shiga toxin production.

Answer: (C)

Enteroaggregative E. coli is defined by its distinctive way of sticking to the intestinal mucosa in a stacked-brick pattern, mediated by aggregative adherence fimbriae. This tight, biofilm-like adherence supports persistent colonization of the gut and leads to a secretory, watery diarrhea rather than tissue invasion. Clinically, EAEC characteristically causes prolonged or persistent watery diarrhea, especially in children and travelers, sometimes with mucus and malabsorption. This pattern helps distinguish it from other E. coli types: attaching-and-effacing E. coli causes lesions via a type III secretion system, invasive pathogens invade mucosa and can produce pus, and Shiga toxin–producing E. coli causes toxin-mediated illness without the same aggregative adherence.