WBR0049
| Author | PageAuthor::William J Gibson |
|---|---|
| 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 ER by his wife for a 3 day history of increasing fever, nausea, vomitting, cough and malaise. On admission, his temperature is 104F, his heart rate is 75 and his respiratory rate is 25. 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::Incorrect - Eaton’s agar is used to culture Mycoplasma Pneumoniae. This organism is not a gram negative rod and it causes atypical pneumonia not the infection seen in this patient. |
| Answer B | AnswerB::Charcoal Yeast Extract |
| Answer B Explanation | AnswerBExp::Correct - Charcoal yeast extract is used to culture Legionella. See explanation. |
| Answer C | AnswerC::Tellurite Agar |
| Answer C Explanation | AnswerCExp::Incorrect - Tellurite agar is used to culture Corynebacterium diptheria. C. Diptheria is largely eliminated from developed countries but causes pharyngitis, and not the pulmonary symptoms seen in this patient. |
| Answer D | AnswerD::Maconkey’s Agar |
| Answer D Explanation | AnswerDExp::Incorrect - 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 |
| Answer E Explanation | AnswerEExp::Incorrect - 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 older individuals, people who are immunocompromised or smokers. 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.
Tags: #Microbiology #Biochemistry |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::WJG |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |