WBR0056

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::General Principles, SubCategory::Infectious Disease
Prompt	[[Prompt::A 55 year old homeless man presents with a 6 month history of a slowly growing lesion in his nasal sinus tracts. Physical exam is notable for poor dentition, a lack of lymphadenopathy and wooden appearance of the nasal lesion with yellow “sulfur” granules. What is the most likely causal organism?]]
Answer A	AnswerA::Staphylococcus Aureus
Answer A Explanation	[[AnswerAExp::Incorrect - Staph Aureus can cause cutaneous infection (eg Impetigo, Cellulitis) but is not associated the deeper infection crossing tissue boundaries seen in this patient. S Aureus is also not associated with with sulfur granules (not to be confused with the yellow pigment S Aureus can produce).]]
Answer B	AnswerB::Nocardia Asteroides
Answer B Explanation	[[AnswerBExp::Incorrect - Nocardia is similar to Actinomyces Israelii in that both are gram-positive rods which form branching filaments, but Nocardia is not associated with sulfur granules and typically causes pulmonary infection in immunocompromised patients.]]
Answer C	AnswerC::Bacillus Anthracis
Answer C Explanation	AnswerCExp::Incorrect- While B. Anthracis can cause cutaneous infections the infected area tends to develop acutely and is darkly colored. Not associated with draining sinus tracts or sulfur granules.
Answer D	AnswerD::Actinomyces Israelii
Answer D Explanation	AnswerDExp::Correct - See Explanation
Answer E	AnswerE::Mycobacterim Leprae
Answer E Explanation	AnswerEExp::Incorrect - Mycobacterium Leprae causes leprosy (Hansen’s disease) which this patient does not have.
Right Answer	RightAnswer::D
Explanation	[[Explanation::The patient in this vignette is suffering from Actinomyces Israelii. Actinomyces Israelii is a facultative anaerobe, part of the normal oral flora and able to cause disease only when it is free to replicate in an anoxic environment. Patients have often recently had dental work, poor oral hygiene, periodontal disease, or radiation therapy causing local tissue damage to the oral mucosa, all of which predispose the person to developing actinomycosis. Educational Objective: References: First Aid 2012 page 159 Tags: #Microbiology #Pathophysiology Educational Objective: References: ]]
Approved	Approved::Yes
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