WBR295

Revision as of 08:01, 7 October 2013 by Gerald Chi (talk | contribs) (Created page with "{{WBRQuestion |QuestionAuthor=Gerald |ExamType=USMLE Step 1 |MainCategory=Microbiology |SubCategory=Gastrointestinal |MainCategory=Microbiology |SubCategory=Gastrointestinal |...")
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search
 
Author PageAuthor::Gerald
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::Gastrointestinal
Prompt [[Prompt::A 29-year-old male presents to the clinic with symptoms of abdominal pain, malaise, and watery diarrhea that begin a day after coming back from a travel to Bangladesh. He complains of orthostatic dizziness and has dry mucosa and decreased skin turgor. Few leukocytes are found in his fecal specimen. Growth of purple colonies on Eosin methylene blue agar is noted. Presence of the heat-labile enterotoxin is confirmed by enzyme-linked immunosorbent assay (ELISA). Which of the following events best describes the action of this toxin?]]
Answer A AnswerA::Increase of intracellular cyclic GMP.
Answer A Explanation AnswerAExp::Increase of intracellular cyclic GMP is mediated by ST.
Answer B AnswerB::Phosphorylation of CFTR by protein kinase A.
Answer B Explanation AnswerBExp::Correct. Phosphorylation of CFTR by protein kinase A is mediated by LT.
Answer C AnswerC::Cytotoxicity to intestinal epithelium.
Answer C Explanation AnswerCExp::Cytotoxicity to intestinal epithelium is mediated by EAEC toxins such as PET.
Answer D AnswerD::Adherence to intestinal epithelium.
Answer D Explanation AnswerDExp::Adherence to intestinal epithelium may be mediated by colonizing factor antigen (CFA) of ETEC, Tir (translocated intimin receptor) of EPEC, or surface adhesins.
Answer E AnswerE::ADP ribosylation of Gi protein.
Answer E Explanation AnswerEExp::ADP-ribosylation of Gi protein is mediated by pertussis toxin.
Right Answer RightAnswer::B
Explanation [[Explanation::Enterotoxigenic Escherichia coli (ETEC) is a type of Escherichia coli and the leading bacterial cause of diarrhea in the developing world, as well as the most common cause of travelers' diarrhea.

Enterotoxins produced by ETEC include heat-labile enterotoxin (LT) and heat-stable enterotoxin (ST). LT activates adenylyl cyclase and increases the amount of cAMP, and results in profound chloride efflux secondary to phosphorylation of CFTR by persistently activated protein kinase A. ST activates guanylyl cyclase in the signal pathway of the enteric epithelial cells and triggers fluid secretion.
Educational Objective:
References: ]]

Approved Approved::No
Keyword WBRKeyword::Escherichia coli
Linked Question Linked::
Order in Linked Questions LinkedOrder::