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 severe pulmonary infection seen in this patient.]]
Answer B	AnswerB::Charcoal Yeast Extract
Answer B Explanation	AnswerBExp::'''Correct:''' Charcoal yeast extract is used to culture Legionella pneumophila, the organism responsible for Legionnaire's disease.
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 and would therefore be unlikely in this patient. C. diptheria infection causes severe pharyngitis accompanied by the development of pseudomembranes that coat the throat and tonsils. The pulmonary symptoms and fever observed in this patient are inconsistent with C. diptheria infection.]]
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 Agar
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 smokers, older individuals, or people who are immunocompromised. 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. References: First Aid 2014 page 138 Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Legionairre's disease, WBRKeyword::Microbiology, WBRKeyword::Bacteria, WBRKeyword::Pneumonia, WBRKeyword::Laboratory
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