Antibiotic susceptibility – novobiocin resistance among staphylococci Which of the following staphylococcal species is classically resistant to novobiocin on diagnostic testing?

Introduction / Context:Novobiocin susceptibility helps differentiate coagulase-negative staphylococci in urinary isolates. A classic mnemonic—“Novobiocin: Sapro-resistant, Epidermidis-sensitive”—guides quick bench decisions.

Given Data / Assumptions:

• All listed organisms are staphylococci relevant to human disease.
• Phenotypic susceptibility patterns are used alongside coagulase testing.
• Clinical context often involves urinary isolates from young women.

Concept / Approach:S. saprophyticus is characteristically resistant to novobiocin, whereas S. epidermidis and most other coagulase-negative staphylococci are sensitive. This pattern supports rapid identification and appropriate reporting from the microbiology lab.

Step-by-Step Solution:Recall mnemonic: “NO StRESS” (Novobiocin: Saprophyticus Resistant, Epidermidis Sensitive).Match to options and select the resistant species.

Verification / Alternative check:Standard lab manuals document S. saprophyticus as novobiocin-resistant; QC organisms confirm disk results.

Why Other Options Are Wrong:

• S. aureus, S. epidermidis, S. lugdunensis: generally novobiocin-sensitive.
• “None”: incorrect because a resistant species is present.

Common Pitfalls:Misreading disk diffusion zones or conflating methicillin resistance with novobiocin resistance; they are unrelated traits.

Final Answer:Staphylococcus saprophyticus.