WBR0046
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Microbiology, MainCategory::Pharmacology |
| Sub Category | SubCategory::Pulmonology, SubCategory::General Principles |
| Prompt | [[Prompt::A 20-year-old woman presents to her primary care physician complaining of dyspnea and malaise. Over the past week she has experienced increasing dyspnea, bronchitis and fatigue which limits her otherwise vigorous exercise but does not interfere with daily activities. She denies abnormal sputum production and any significant past medical history. On physical examination, she has a pulse of 72 beats/min, temperature of 101 F (38.3 C), respiratory rate of 22/min and oxygen saturation of 94% on room air. Cardiac examination is normal but respiratory exam reveals diffuse crackles. Which of the following is true of the most likely causal organism?]] |
| Answer A | AnswerA::Chloramphenicol |
| Answer A Explanation | AnswerAExp::'''Incorrect:''' Chloramphenicol is not the drug of choice for Mycoplasma infection. Chloramphenicol is known for causing Gray baby syndrome. |
| Answer B | AnswerB::Trimethoprim-Sulfamethoxazole (Bactrim) |
| Answer B Explanation | AnswerBExp::TMP-SMX is not the drug of choice for Mycoplasma infection. TMP-SMX is often used for simple UTIs/cystitis. |
| Answer C | AnswerC::Erythromycin |
| Answer C Explanation | AnswerCExp::Erythromycin is a macrolide antibiotic that blocks the 50s ribosomal subunit and can be used to treat Mycoplasma pneumoniae infection. |
| Answer D | AnswerD::Penicillin |
| Answer D Explanation | AnswerDExp::Penicillin is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall. |
| Answer E | AnswerE::Aztreonam |
| Answer E Explanation | AnswerEExp::Aztreonam, a beta-lactam antibiotic resistant to beta-lactamases, is ineffective against Mycoplasma infections because mycoplasma lacks a peptidoglycan cell wall. |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient is suffering from a case of atypical pneumonia, a respiratory infection which often causes systemic symptoms such as fever, headache and myalgia. Atypical pneumonia differs from typical pneumonia in that atypical pneumonias often do not respond to common antibiotics (eg sulfonamides, or beta-lactams), do not show signs of consolidation, nor give rise toe leukocytosis. On chest X-ray, patients often show a diffuse interstitial infiltrate which conveys the appearance of a more severe infection than the patient’s symptoms suggest. Because patients often have mild symptoms, atypical pneumonia is alternatively referred to as “walking pneumonia.” While walking pneumonia due to mycoplasma infection is a distinct entity, the more general distinction between typical and atypical pneumonias is largely historical and has more recently been de-emphasized.
Atypical pneumonia is most often caused by Mycoplasma pneumoniae which usually infects older children and young adults (patients <30 years old). Mycoplasma pneumoniae is a mere 0.3 um in size and is the only bacteria which does not possess a cell wall. Mycoplasma pneumoniae can be cultured on Eaton's agar. Mycoplasma pneumonia can be treated with macrolides (eg erythromycin) or tetracyclines. Note: This question is linked to WBR0044, WBR0045 |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Microbiology, WBRKeyword::Mycoplasma, WBRKeyword::Bacteria, WBRKeyword::Pneumonia, WBRKeyword::Infection, WBRKeyword::Antibiotics, WBRKeyword::Drug, WBRKeyword::Drugs, WBRKeyword::Pharmacology |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |