Gram-positive cocci in clusters, catalase positive, novobiocin resistant. Which organism most likely?

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When you have gram-positive cocci arranged in clusters and they are catalase positive, you’re dealing with Staphylococcus species. To identify the exact organism, you can use the novobiocin susceptibility pattern. Among the staphylococci, Staphylococcus saprophyticus is notable for being resistant to novobiocin, while most other common coagulase-negative staphylococci (like Staphylococcus epidermidis) are sensitive. So the combination of clustering, catalase positivity, and novobiocin resistance points to Staphylococcus saprophyticus.

This helps distinguish it from other possibilities: Staphylococcus aureus is typically coagulase positive, not the novobiocin-resistance pattern highlighted here, and while Streptococcus pneumoniae is catalase negative and does not form clusters, the described test pattern aligns best with Staphylococcus saprophyticus.