WBR0054
Author | PageAuthor::William J Gibson |
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Exam Type | ExamType::USMLE Step 1 |
Main Category | MainCategory::Microbiology |
Sub Category | SubCategory::Head and Neck, SubCategory::Neurology, SubCategory::General Principles, SubCategory::Infectious Disease |
Prompt | [[Prompt::A 5-year-old boy from rural Africa has recently immigrated to the United States with his family. His father brings him to the emergency room, where the patient is found to have a fever of 100.7 F (38.2 C), fatigue, and severe pharyngitis. Physical exam reveals marked cervical lymphadenopathy, and pseudomembranes in the throat. A throat swab is performed which reveals gram positive bacilli. What is the mechanism of action of the toxin produced by the causative organism?]] |
Answer A | AnswerA::Inactivate 60S ribsosome by cleaving rRNA |
Answer A Explanation | AnswerAExp::The toxins produced by Shigella and EHEC inactivate the 60S ribosome by cleaving rRNA. |
Answer B | AnswerB::Activates adenylate cyclase by stimulating Gs |
Answer B Explanation | AnswerBExp::The toxin produced by Vibrio cholera activated adenylate cyclase by stimulating Gs. This activation of the cAMP pathway in enterocytes leads to a secretory diarrhea. A hallmark of Cholera is the development of "rice-water" stools. |
Answer C | AnswerC::Activates adenylate cyclase by disabling Gi |
Answer C Explanation | AnswerCExp::The toxin produced by Bordetella pertussis activates adenylate cyclase by disabling Gi. Pertussis infection represents a highly contagious bacterial disease that manifests as "whooping cough". |
Answer D | AnswerD::Cleaves SNARE protein |
Answer D Explanation | AnswerDExp::Both Botulinum and Tetanus toxin cleave SNARE protein at synapses, thereby disabling neurotransmitter release at the synaptic cleft. |
Answer E | AnswerE::Inactivate EF-2 |
Answer E Explanation | AnswerEExp::Diptheria toxin causes disease by inactivating Elongation Factor 2 (EF-2). Diptheria infection can be diagnosed by the presence of pseudomembranes in the throat. |
Right Answer | RightAnswer::E |
Explanation | [[Explanation::This patient is suffering from an infection caused by Corynebacterium diptheriae, a gram positive rod that has mostly been eradicated in the developed world through vaccination. Diptheria causes upper respiratory tract infections with sore throat and low-grade fever. The hallmark of this infection is an adherent true membrane on the tonsils referred to as pseudomembranes. Educational Objective: Diptheria toxin causes disease by inactivating Elongation Factor 2 (EF-2). Diptheria infection can be diagnosed by the presence of pseudomembranes in the throat. |
Approved | Approved::Yes |
Keyword | WBRKeyword::Microbiology, WBRKeyword::Diptheria, WBRKeyword::Toxin, WBRKeyword::Bacteria, WBRKeyword::Mechanism |
Linked Question | Linked:: |
Order in Linked Questions | LinkedOrder:: |