WBR0945
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| Author | [[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]] |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Microbiology |
| Sub Category | Genitourinary |
| Prompt | A sexually active 22-year-old woman presents to her primary care physician with complaints of burning sensation on urination for the past 2 days. Urine culture demonstrates colonies of catalase-positive, coagulase-negative, gram-positive cocci with novobiocin resistance. Which of the following pathogen's is most likely responsible for this patient's condition? |
| Answer A | Escheria coli |
| Answer A Explanation | While E. coli is the leading cause of urinary tract infections among sexually active women, E.coli is a gram-negative rod. |
| Answer B | Staphylococcus aureus |
| Answer B Explanation | While S. aureus is a catalase-positive, gram-positive coccus, it is coagulase-positive. |
| Answer C | Staphylococcus epidermidis |
| Answer C Explanation | S. epidermidis is a catalase-positive, coagulase-negative, gram-positive coccus with novobiocin sensitivity. S. epidermidis is a component of the normal skin flora but can become pathogenic typically by infecting prosthetic devices. It is a common cause of endocarditis among patients with artificial valves. |
| Answer D | Staphylococcus saprophyticus |
| Answer D Explanation | S. Saprophyticus is a catalase-positive, coagulase-negative, gram-positive coccus with novobiocin resistance. It is the second most common cause of urinary tract infections among sexually active women, following E. coli. |
| Answer E | Streptococcus agalactiae |
| Answer E Explanation | S agalactiae is a catalase-negative, beta-hemolytic, gram-positive coccus with bacitracin resistance. It is alternatively referred to as Group B streptococci and is a common cause of neonatal meningitis. |
| Right Answer | D |
| 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 coccus with novobiocin resistance. It is the second most common cause of urinary tract infections among sexually active women (10-20%) following E. coli. Educational Objective: S. Saprophyticus is a catalase-positive, coagulase-negative, gram-positive coccus with novobiocin resistance. It is the second most common cause of urinary tract infections among sexually active women. |
| Approved | Yes |
| Keyword | Bacteria, Staphylococcus saprophyticus, Gram positive, Gram positive bacteria, UTI, Urinary tract infection, Laboratory classification, Catalase, Novobiocin, Coagulase |
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