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Microbiology 25

A 16-year-old boy presents to the emergency department with complaints of several episodes of bloody diarrhea, stomach cramps, and weakness since yesterday evening. He also says, "I am constantly feeling like I have to go to the bathroom, even when there's nothing left to pass." He has recently returned from a vacation in Nepal. He is currently not on any medication. Vital signs are temperature 38.6° C (101.4° F), blood pressure 88/62 mmHg, pulse 127 beats/min, and respirations 25/min. On physical examination, the lower abdomen is tender to palpation, and there are increased bowel sounds.

A complete blood count (CBC) reveals the following relevant findings:
Hemoglobin: 9.5 g/dL
Total Leukocyte count: 15,000/mm3

ESR and CRP are elevated. Stool analysis is positive for fecal leukocytes and blood. Stool culture yields green colonies on Hektoen agar. Which of the following best explains the pathogenicity of the most likely causative organism?

  • A) Active efflux of electrolytes from the intestinal epithelium into the lumen
  • B) Evasion of host immune response by the neutralization of hydrogen peroxide
  • C) Exotoxin-mediated depolymerization of the host cell actin cytoskeleton
  • D) Exotoxin-mediated inhibition of mitogen-activated protein kinase (MAP-Kinase) signaling
  • E) Invasion of microfold (M) cells


Arihant Senthil


Dr. Ted O'Connell

Last updated

Sep 04, 2023

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