Correct Pathogen-Mechanism Match for Diarrhea
Option A is correct: Clostridium difficile causes diarrhea through a toxin-mediated mechanism. 1, 2
Pathophysiologic Mechanisms by Pathogen
Clostridium difficile – Toxin-Mediated (CORRECT)
C. difficile produces toxins A and B that bind to intestinal epithelial cells, become internalized, and induce apoptosis, leading to diarrhea. 1, 3, 4
- The toxins glucosylate and inactivate Rho GTP-binding proteins in the cytosol, disrupting the cytoskeleton and causing loss of epithelial barrier function, inflammation, and cell death 4
- This is a classic toxin-mediated mechanism where the organism colonizes the gut after antibiotic disruption of normal flora, then releases toxins that directly damage the intestinal mucosa 1, 3
- C. difficile accounts for up to 50% of all antibiotic-associated diarrhea cases through this toxin-mediated pathophysiology 1
Enterotoxigenic E. coli – NOT a Preformed Toxin Producer (INCORRECT)
ETEC produces toxins in vivo after colonization, not preformed toxins ingested with food. 1, 5
- ETEC synthesizes heat-stable enterotoxin (ST) and heat-labile enterotoxin (LT) after adhering to the small intestinal mucosa 1, 5
- These toxins increase cyclic AMP/GMP, causing secretory diarrhea, but are produced by living bacteria in the gut, not preformed in food like Staphylococcus aureus toxin 5
Salmonella – Invasive with Variable Inflammation (PARTIALLY CORRECT but not the best match)
While Salmonella does invade intestinal epithelium and cause variable inflammation, this description is less specific than the C. difficile toxin-mediated mechanism. 1
- Salmonella penetrates the intestinal mucosa and can cause inflammatory diarrhea with fever, bloody stools, and fecal leukocytes 1
- However, the mechanism is more complex than simple invasion, involving both invasive properties and inflammatory responses 1
Vibrio cholerae – NOT Invasive (INCORRECT)
V. cholerae causes diarrhea through cholera toxin, not mucosal invasion. 1, 6
- Cholera toxin increases adenylate cyclase activity and cAMP production, resulting in massive fluid and electrolyte secretion into the intestinal lumen without mucosal invasion 1, 6
- This is a purely toxin-mediated secretory diarrhea mechanism; the organism does not invade or cause mucosal inflammation 1, 6
- The pathogenesis produces the characteristic "rice water" stools through toxin action on enterocytes, not through invasion 6
Key Distinguishing Features
Toxin-mediated diarrhea (C. difficile, V. cholerae) occurs without bacterial invasion of the mucosa, while invasive pathogens (Salmonella, Shigella) penetrate epithelial cells and cause inflammatory responses. 1, 5