WBR0050
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Pulmonology, SubCategory::General Principles, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 52 year old alcoholic and homeless male presents to the emergency room after coughing up blood. He has experienced increasing cough over the past 2 weeks after recovering from an upper respiratory tract infection. His temperature is 101.5F and a chest X-ray reveals a right upper lobe opacity with right sided hilar adenopathy. Which of the following media could be used to isolate the most likely causal organism?]] |
| Answer A | AnswerA::Eaton's agar |
| Answer A Explanation | [[AnswerAExp::Incorrect: Eaton’s agar can be used to culture mycoplasma pneumonia.]] |
| Answer B | AnswerB::Charcoal yeast extract |
| Answer B Explanation | [[AnswerBExp::Incorrect: Charcoal yeast extract can be used to culture Legionella pneumophila].]] |
| Answer C | AnswerC::Maconkey’s agar |
| Answer C Explanation | [[AnswerCExp::Incorrect: Maconkey’s agar is used to culture a variety of organisms but cannot be used to culture Mycobacterium tuberculosis.]] |
| Answer D | AnswerD::Tellurite agar |
| Answer D Explanation | [[AnswerDExp::Incorrect: Tellurite agar can be use to culture Corynebacterium diptheria.]] |
| Answer E | AnswerE::Lowenstein-Jensen agar |
| Answer E Explanation | AnswerEExp::'''Correct:''' Lowenstein-Jensen agar can be used to culture Mycobacterium tuberculosis, the causal organism in this vignette. |
| Right Answer | RightAnswer::E |
| Explanation | [[Explanation::The patient in this vignette is suffering from tuberculosis. He has several risk factors for TB including homelessness and alcoholism. Some other infections such as Klebsiella are known for causing pneumonia in alcoholics, typically due to aspiration of oral flora. However, these infections typically cause lower lobe consolidation. Conversely, reactivation mycobacterium prefers to grow in the highly oxygenated upper lobes of the lung and is often accompanied by unilateral enlargement of the hilar lymph nodes. Mycobacterium tuberculosis can be cultured on Lewenstein-Jensen media, but the culture process takes approximately 4 weeks due to the slow doubling time of mycobacterium tuberculosis.
Educational Objective: Mycobacterium tuberculosis can cause reactivation TB in alcoholics and can be cultured on Lowenstein-Jensen agar. References: First Aid 2014 page 134 (reactivation TB) First Aid 2014 page 122 (culture conditions) |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Tuberculosis, WBRKeyword::TB, WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Laboratory, WBRKeyword::Alcoholism, WBRKeyword::Pulmonary |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |