Staphylococcus saprophyticus can be differentiated from other causes of cystitis by resistance to which antibiotic?

Staphylococcus saprophyticus can be differentiated from other causes of cystitis by resistance to which antibiotic?

• A. Penicillin
• B. Vancomycin
• C. Novobiocin
• D. Methicillin

Answer: (C)

Novobiocin resistance is the clue used to identify Staphylococcus saprophyticus in urinary isolates. This organism is typically resistant to novobiocin, while other common coagulase-negative staphylococci, such as Staphylococcus epidermidis, are inhibited by it. In the lab, a urine isolate that can grow near a novobiocin disk signals resistance and points to Staphylococcus saprophyticus as the cause of the cystitis. This distinction is particularly helpful because S. saprophyticus is a notable cause of uncomplicated cystitis in young, sexually active women. The other antibiotics listed aren’t diagnostic for this organism—penicillin resistance is widespread among staphylococci and isn’t specific, and vancomycin or methicillin testing is more about broader resistance concerns (MRSA/VRSA) than identifying this species in UTIs.

Novobiocin resistance is the clue used to identify Staphylococcus saprophyticus in urinary isolates. This organism is typically resistant to novobiocin, while other common coagulase-negative staphylococci, such as Staphylococcus epidermidis, are inhibited by it. In the lab, a urine isolate that can grow near a novobiocin disk signals resistance and points to Staphylococcus saprophyticus as the cause of the cystitis. This distinction is particularly helpful because S. saprophyticus is a notable cause of uncomplicated cystitis in young, sexually active women. The other antibiotics listed aren’t diagnostic for this organism—penicillin resistance is widespread among staphylococci and isn’t specific, and vancomycin or methicillin testing is more about broader resistance concerns (MRSA/VRSA) than identifying this species in UTIs.