A blood culture from an immunocompromised patient grows an organism that is catalase-positive, coagulase-negative, novobiocin-resistant, and forms a yellow pigment on nutrient agar. Which Staphylococcus species is most likely, and what is its clinical significance?
- A S. saprophyticus — urinary tract infections in sexually active young women ✓
- B S. epidermidis — prosthetic device-associated infections
- C S. lugdunensis — aggressive endocarditis mimicking S. aureus
- D S. haemolyticus — increasing glycopeptide MIC creep
Correct answer: A. S. saprophyticus — urinary tract infections in sexually active young women
Explanation
Novobiocin resistance distinguishes S. saprophyticus from other clinically important CoNS (S. epidermidis, S. haemolyticus and S. lugdunensis are all novobiocin-sensitive). S. saprophyticus is a common cause of uncomplicated UTI in sexually active young women and can cause bacteraemia in immunocompromised patients. Yellow pigment production is variable across species, but combined with novobiocin resistance, S. saprophyticus is the correct identification. S. lugdunensis is novobiocin-sensitive and is known for aggressive native valve endocarditis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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