WBR0054
| Author | PageAuthor::William J Gibson |
|---|---|
| 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, 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::'''Incorrect:''' 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::Incorrect: 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::'''Incorrect:''' 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::'''Incorrect:''' 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::'''Correct:''' 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 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.
References: First Aid 2014 pages 132 (diptheria), 126 (toxins) First Aid 2012 page 152. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Diptheria, WBRKeyword::Toxin, WBRKeyword::Bacteria, WBRKeyword::Mechanism |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |