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 distinguishing feature used to separate Staphylococcus saprophyticus from other urinary pathogens. In the lab, a novobiocin susceptibility test shows S. saprophyticus as resistant, so it grows near the disk, while most other common urinary pathogens are inhibited by novobiocin. This pattern provides a practical way to identify S. saprophyticus in cystitis, especially in young sexually active women. Other antibiotics listed don’t offer the same reliable differentiation: penicillin resistance is common across many Staphylococcus species and isn’t specific to this organism, and vancomycin or methicillin tests are more about treatment choices and MRSA screening than distinguishing S. saprophyticus in UTIs.