WBR0045

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Pulmonology
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 examination, her pulse is 72, temperature of 101 F (38.3 C), respiratory rate of 22 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 causal organism?]]
Answer A	AnswerA::Pili undergo antigenic variation
Answer A Explanation	AnswerAExp::False. The pili of Neisseria Gonnorhea undergo antigenic variation.
Answer B	AnswerB::Cell wall contains cholesterol
Answer B Explanation	AnswerBExp::False. The Mycoplasma Pneumonia does not have a cell wall. Its cell membrane however, incorporates sterol compounds such as cholesterol. It is the only bacterial membrane which contains cholesterol.
Answer C	AnswerC::Acid fast bacilli
Answer C Explanation	AnswerCExp::False. Mycobateria species stain positive in acid fast stain, but mycoplasma are not identified in this manner.
Answer D	AnswerD::Positive silver stain
Answer D Explanation	AnswerDExp::The causal organism in this vignette is Myocplasma Pneumonia which is not detected by silver stain. Organisms which are stained with silver include Pseudomonas, Legionella, Leptospira, H. Pylori, and fungi such as Pneumocystis, and Candida.
Answer E	AnswerE::No cell wall
Answer E Explanation	AnswerEExp::True. See explanation.
Right Answer	RightAnswer::E
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 it does not respond to common antibiotics (eg sulfonamides, or beta-lactams), does not show signs of consolidation, nor leukocytosis. On chest X-ray, patients often show 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.” Atypical pneumonia is most often caused by Mycoplasma Pneumonia which usually occurs in older children and young adults (patients <30 years old). Mycoplasma Pneumonia is a mere 0.3 um in size and is the only bacteria which does not possess a cell wall. Educational Objective: Mycoplasma Pneumonia is the most common cause of atypical pneumonia, it lacks a cell wall. References: First Aid 2012 pg 147,170. Tags: #Microbiology #Pathophysiology Educational Objective: References: ]]
Approved	Approved::Yes
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