Most common strain of E.coli giving rise to traveller’s diarrhea is –
**Core Concept**
The question is testing the student's knowledge of the pathogenesis of traveler's diarrhea, specifically the most common strain of E.coli responsible. **Enterotoxigenic E. coli (ETEC)** is a heat-labile toxin (LT) and/or heat-stable toxin (ST) producing pathotype that commonly causes traveler's diarrhea.
**Why the Correct Answer is Right**
ETEC is the most common cause of traveler's diarrhea, particularly in individuals traveling to developing countries. **The heat-labile toxin (LT)**, also known as cholera toxin, and **the heat-stable toxin (ST)**, also known as STa or STb, **are produced by ETEC strains** and lead to the secretion of water and electrolytes into the intestinal lumen, resulting in diarrhea. ETEC adheres to the small intestinal mucosa and releases these toxins, which activate the adenylate cyclase pathway, increasing cyclic AMP levels and leading to the secretion of chloride and water.
**Why Each Wrong Option is Incorrect**
* **Option A:** EIEC (Enteroinvasive E. coli) is a pathotype that invades and multiplies within the intestinal epithelial cells, causing a dysentery-like syndrome. It is not the most common cause of traveler's diarrhea.
* **Option B:** EAEC (Enteroaggregative E. coli) is a pathotype that forms biofilm aggregates on the surface of intestinal epithelial cells, leading to persistent diarrhea. However, it is not the most common cause of traveler's diarrhea.
* **Option C:** EHEC (Enterohemorrhagic E. coli) is a pathotype that produces Shiga toxins, leading to bloody diarrhea and hemolytic uremic syndrome. It is not typically associated with traveler's diarrhea.
**Clinical Pearl / High-Yield Fact**
Traveler's diarrhea can be prevented by using oral rehydration solutions, probiotics, and antimicrobial agents such as rifaximin. Additionally, vaccines against ETEC are available for individuals traveling to high-risk areas.
**Correct Answer:** C. ETEC