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::Incorrect: 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::Incorrect: 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::Incorrect: 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::Correct: 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::Incorrect: 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: First Aid 2013 page 127 (gram positive diagram) First Aid 2013 page 170 (UTI summary) |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Bacteria, WBRKeyword::Gram positive, WBRKeyword::Gram positive bacteria, WBRKeyword::UTI |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |