Which pathotype produces toxins that disrupt fluid balance and cause watery diarrhea without invasion?

• A. Enteropathogenic E. coli produces attaching and effacing lesions.
• B. Enterotoxigenic E. coli produces LT/ST toxins that disrupt fluid balance and cause watery diarrhea without invasion.
• C. Shiga toxin-producing E. coli produces Shiga toxin.
• D. Enteroaggregative E. coli adheres via stacked-brick pattern.

Answer: (B)

The key idea is identifying a pathotype that causes watery, noninvasive diarrhea through toxin-driven secretions rather than mucosal invasion. Enterotoxigenic E. coli makes two classic toxins, LT and ST. LT raises cAMP in intestinal cells, triggering chloride and water secretion; ST raises cGMP, also promoting secretion. This results in a watery, nonbloody diarrhea without invasion of the mucosa. In contrast, enteropathogenic E. coli causes attaching and effacing lesions without relying on secretory toxins, Shiga toxin–producing E. coli (EHEC) produces Shiga toxin and can be invasive with potential systemic effects and bloody stool, and enteroaggregative E. coli adheres in a stacked-brick pattern and forms biofilms, often causing more persistent symptoms.