WBR0945

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Microbiology
Sub Category	SubCategory::Genitourinary, SubCategory::Infectious Disease
Prompt	[[Prompt::A sexually active 22-year old woman presents to her primary care physician with burning on urination. Urine culture reveals colonies of catalase positive, coagulase negative, gram-positive cocci with novobiocin resistance. Which of the following is the most likely causal organism?]]
Answer A	AnswerA::Escheria coli
Answer A Explanation	AnswerAExp::While E. Coli is the leading cause of urinary tract infections in sexually active women, E.Coli is a gram-negative rod.
Answer B	AnswerB::Staphylococcus aureus
Answer B Explanation	AnswerBExp::While S. aureus is a catalase positive, gram-positive cocci, it is coagulase negative. Furthermore, S. aureus is not a common cause of urinary tract infections.
Answer C	AnswerC::Staphylococcus epidermidis
Answer C Explanation	[[AnswerCExp::S. epidermidis is a catalase positive, coagulase negative, gram-positive cocci with novobiocin sensitivity. S. epidermidis is a component of the normal skin flora, but can become pathogenic by infecting prosthetic devices. It is a common cause of endocarditis in patients with artificial valves.]]
Answer D	AnswerD::Staphylococcus saprophyticus
Answer D Explanation	AnswerDExp::S. Saprophyticus is a catalase positive, coagulase negative, gram-positive cocci with novobiocin resistance. It is the second most common cause of urinary tract infections in sexually active women, behind E. coli.
Answer E	AnswerE::Streptococcus agalactiae
Answer E Explanation	AnswerEExp::S agalactiae is a catalase negative, beta-hemolytic, gram-positive cocci with bacitracin resistance. It is alternatively referred to as Group B streptococci and is a common cause of neonatal meningitis.
Right Answer	RightAnswer::D
Explanation	[[Explanation::The patient in this vignette has a urinary tract infection caused by Staphylococcus saprophyticus. S. Saprophyticus is a catalase positive, coagulase negative, gram-positive cocci with novobiocin resistance. It is the second most common cause of urinary tract infections in sexually active women (10-20%), behind E. coli. A useful mnemonic to remember the drug resistance of staphylococci is: On the office's staph retreat, there was NO StRESs. NOvobiocin: Saprophyticus is Resistant, Epidemidis is Sensitive Educational Objective: S. saprophyticus is novobiocin resistant and the second most common cause of urinary tract infections in sexually active young women. References: Hovelius, Birgitta, and Per-Anders Mardh. "Staphylococcus saprophyticus as a common cause of urinary tract infections." Review of Infectious Diseases 6.3 (1984): 328-337. First Aid 2015 page 127 (gram positive diagram) First Aid 2015 page 174 (UTI summary)]]
Approved	Approved::Yes
Keyword	WBRKeyword::Bacteria, WBRKeyword::Gram positive, WBRKeyword::Gram positive bacteria, WBRKeyword::UTI, WBRKeyword::Urinary tract infection, WBRKeyword::Laboratory classification, WBRKeyword::Catalase
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