Which organism exhibits stacked-brick adherence pattern and causes persistent watery diarrhea?

• A. Enteropathogenic E. coli (EPEC) exhibits attaching and effacing lesions.
• B. Shigella causes dysentery.
• C. ETEC produces LT/ST toxins.
• D. Enteroaggregative E. coli exhibits stacked-brick adherence pattern and causes persistent watery diarrhea.

Answer: (D)

The main idea here is recognizing a distinctive adherence pattern that points to a specific cause of persistent watery diarrhea. Enteroaggregative Escherichia coli is known for its stacked-brick adherence on intestinal cells, a pattern caused by aggregative adherence fimbriae that make the bacteria line up in a brick-like array and form a biofilm on the intestinal mucosa. This type of adherence supports prolonged colonization and ongoing secretion of fluid, which manifests as persistent watery diarrhea, a hallmark of EAEC infections.

Other choices fit different diarrheal diseases but not this pattern. EPEC forms attaching and effacing lesions with pedestal-like changes on enterocytes, producing infantile or acute diarrhea rather than persistent watery diarrhea. Shigella invades the mucosa leading to dysentery with blood and neutrophils, not a persistent watery pattern. ETEC causes toxin-mediated watery diarrhea, often acute and self-limited, but it does not exhibit the stacked-brick adherence pattern.