Spectrum of novobiocin — Against which organisms is novobiocin classically useful in clinical microbiology?

Introduction / Context:
Novobiocin is a coumarin antibiotic that inhibits bacterial DNA gyrase. Its utility lies predominantly against Gram-positive organisms, especially staphylococci, and it is famously used in laboratory testing to differentiate Staphylococcus saprophyticus (novobiocin-resistant) from other coagulase-negative staphylococci (novobiocin-susceptible).

Given Data / Assumptions:

• Gram-negative pathogens listed (Neisseria meningitidis, N. gonorrhoeae, Haemophilus) are not classic targets of novobiocin.
• Staphylococci, particularly S. epidermidis and many other coagulase-negative species, are generally susceptible in vitro.

Concept / Approach:
Match novobiocin’s spectrum with the organisms provided. Select the Gram-positive target group (staphylococci) as the best answer consistent with traditional lab and clinical knowledge.

Step-by-Step Solution:

Verification / Alternative check:
Lab practice uses the novobiocin disk diffusion test to separate S. saprophyticus (resistant) from other staphylococci (susceptible), confirming its relevance to staphylococci.

Why Other Options Are Wrong:

• Gram-negative meningococci/gonococci: not standard novobiocin targets.
• Haemophilus: also Gram-negative; not a typical indication.
• All of these: incorrect due to the above.

Common Pitfalls:
Assuming all DNA gyrase inhibitors behave like fluoroquinolones; novobiocin’s clinical niche is different and limited.

Final Answer:
gram +ve Staphylococci