Which feature aids isolation of staphylococci from clinical specimens?

• A. High salt tolerance
• B. Growth at 55°C
• C. Bile resistance
• D. Resistance to novobiocin

Answer: (A)

Selective isolation of Staphylococcus from clinical specimens relies on their ability to tolerate high salt concentrations. Media like Mannitol Salt Agar use a high NaCl content (around 7.5% or more) to create an environment that inhibits most competing bacteria, while staphylococci can grow readily. This makes it easier to separate them from mixed flora right at the outset. The differential aspect on the same medium (mannitol fermentation) helps identify S. aureus later, but the key isolation feature is surviving the salty conditions.

Growth at 55°C is not a trait used to isolate Staphylococcus, since most staphylococci don’t require or thrive at such elevated temperatures. Bile resistance is more relevant to organisms adapted to the intestinal environment and is not a general basis for isolating Staphylococcus from non-enteric clinical specimens. Resistance to novobiocin is useful for differentiating certain species (like distinguishing S. saprophyticus from others) rather than for initial isolation from specimens.