WBR0049
| Author | [[PageAuthor::William J Gibson (Reviewed by Rim Halaby, M.D. [1])]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Pulmonology, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 57-year-old man is brought to the emergency room by his wife for a 3 day history of increasing fever, nausea, vomiting, cough and malaise. On admission, his temperature is 104 °F, his heart rate is 75 beats/min and his respiratory rate is 25/min. Sputum culture reveals a gram negative rod. Which of the following media could be used to isolate the causal organism?]] |
| Answer A | AnswerA::Eaton’s Agar |
| Answer A Explanation | [[AnswerAExp::Eaton’s agar is used to culture Mycoplasma pneumoniae. This organism is not a gram negative rod and it causes atypical pneumonia, not the severe pulmonary infection seen in this patient.]] |
| Answer B | AnswerB::Charcoal yeast extract |
| Answer B Explanation | [[AnswerBExp::Charcoal yeast extract is used to culture Legionella pneumophila, the organism responsible for Legionnaire's disease.]] |
| Answer C | AnswerC::Tellurite Agar |
| Answer C Explanation | [[AnswerCExp::Tellurite agar is used to culture Corynebacterium diphtheriae. C. diptheria is largely eliminated from developed countries and would therefore be unlikely in this patient. C. diptheria infection causes severe pharyngitis accompanied by the development of pseudomembranes that coat the throat and tonsils. The pulmonary symptoms and fever observed in this patient are inconsistent with C. diptheria infection.]] |
| Answer D | AnswerD::Maconkey’s Agar |
| Answer D Explanation | [[AnswerDExp::Maconkey’s agar is used to culture a variety of organisms. Lactose-fermenting enterics (eg E.Coli) will appear as pink colonies.]] |
| Answer E | AnswerE::Sabouraud’s Agar |
| Answer E Explanation | [[AnswerEExp::Sabouraud’s agar is used to culture fungi.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient in this vignette is suffering from Legionnaire’s disease, a severe pulmonary infection caused by Legionella pneumophila. Legionnaire’s disease typically affects smokers, older individuals, or people who are immunocompromised. Healthy individuals often have a less severe infection called Pontiac fever. Legionnaire’s disease requires treatment with antibiotics and aggressive pulmonary management to resolve. Depending on age and medical condition, Legionnaire’s disease has between a 5% and 30% mortality rate. Educational Objective: Legionella pneumophila causes acute respiratory disease and can be cultured using charcoal yeast agar. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Legionairre's disease, WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Pneumonia, WBRKeyword::Laboratory |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |