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 Educational Objective: References: ]]
Approved	Approved::Yes
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