WBR0253
| Author | [[PageAuthor::Ogheneochuko Ajari, MB.BS, MS [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology |
| Sub Category | SubCategory::Pulmonology, SubCategory::Infectious Disease |
| Prompt | [[Prompt::A 46- year old malnourished man presents to the emergency room with complaints of severe headache, fever, cough and difficulty with breathing. He is a chronic alcoholic and lives in a shelter for the homeless. Physical examination reveals a temperature of 40C, blood pressure of 120/80mmHg, pulse of 96/minute. Auscultation of the chest revealed consolidation over the right middle lung fields. Sputum stain reveals an aerobic, partially acid-fast rod. Which of the following is the likely etiologic agent?]] |
| Answer A | AnswerA::Actinomyces israelii |
| Answer A Explanation | AnswerAExp::Actinomyces israelii is a non-acid fast anaerobic gram-positive rod, forming long branching filaments resembling fungi. |
| Answer B | AnswerB::Mycobacterium avium-intracellulare |
| Answer B Explanation | [[AnswerBExp::Mycobacterium avium-intracellulare (MAI) is an atypical acid-fast mycobacteria, non-contagious and found in surface waters, soil, cigarettes. Transmission is usually via the GI tract and the lungs. It causes disseminated disease in AIDS, cancer and chronic lung disease. It is differentiated from mycobacterium kansasii on the basis of production of carotenoid pigments. MAI is a nonchromogen that produces no pigments.]] |
| Answer C | AnswerC::Streptococcus pneumonia |
| Answer C Explanation | AnswerCExp::Streptococcus pneumonia is a gram-positive alpha hemolytic lancet-shaped diplococci. It is not acid fast. |
| Answer D | AnswerD::Nocardia asteroides |
| Answer D Explanation | AnswerDExp::Nocardia asteroides is an aerobic gram-positive branching rod that is partially acid fast. It causes pulmonary infections especially in immunocompromised individuals. |
| Answer E | AnswerE::Mycobacterium kansasii |
| Answer E Explanation | AnswerEExp::Mycobacterium kansasii is an atypical acid-fast mycobacteria producing pulmonary TB-like symptoms such as fever, night sweats, weight loss and hemoptysis. It is a photochromogen that produces pigment after exposure to light. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::This is a case of Nocardiosis, caused by Norcardia asteroides. It is an aerobic gram-positive branching rod that is partially acid fast. It causes pulmonary infections especially in immunocompromised individuals. Nocardiosis is an infectious disease affecting either the lungs (pulmonary nocardiosis) or the whole body (systemic nocardiosis). It is most common in men, especially those with a compromised immune system. In patients with brain infection, mortality exceeds 80%; in other forms, mortality is 50%, even with appropriate therapy. Severely immunocompromised persons are at greatest risk for nocardiosis. These include persons with connective tissue disorders, malignancy, HIV infection, pulmonary alveolar proteinosis, alcoholism, or high-dose corticosteroid use. Educational Objective: Nocardia asteroides is an aerobic gram-positive partially acid-fast rod that causes nocardiosis. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Gram positive, WBRKeyword::Bacteria |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |